The investigation began when affected birds from a commercial poultry operation in southern Peru were submitted for laboratory diagnosis during a confirmed Newcastle disease outbreak in 2025. The researchers assembled a panel of 105 pooled samples taken from the affected birds and screened them using real-time reverse transcription polymerase chain reaction assays targeting two regions of the viral genome: the matrix gene, or M gene, which encodes an internal structural protein involved in virion assembly, and the fusion gene, or F gene, which encodes the surface glycoprotein responsible for merging the viral envelope with host cell membranes. This dual-target approach is standard practice in NDV diagnostics because it increases sensitivity and provides an early indication of whether a detected virus is likely to be virulent. NDV RNA was detected in 73 of the 105 pools, a positivity rate of 69.5 percent, and 95.9 percent of the detected strains were classified as virulent based on the molecular markers recovered during screening.

From the positive pools, the team selected thirteen samples with cycle threshold values of 25 or lower, a cutoff indicating high viral loads suitable for downstream work. Each of these samples was used to attempt virus isolation in embryonated chicken eggs, the classical method for propagating avian viruses in the laboratory, in which inoculated eggs are incubated and the allantoic fluid is later harvested for testing. All thirteen isolates replicated successfully, exhibiting the hallmarks of highly pathogenic NDV: embryo mortality following inoculation, strong hemagglutinating activity reflecting the activity of the hemagglutinin-neuraminidase protein in binding red blood cells, and high titers expressed as the 50 percent egg infectious dose, or EID50. These phenotypic observations were fully consistent with the genetic evidence of virulence recovered later during sequencing and provided independent confirmation that a highly pathogenic virus was circulating in the affected flocks.

Sequencing was performed using Oxford Nanopore Technologies, a platform that reads long DNA molecules and can generate complete viral genomes rapidly and at relatively low cost, an advantage for laboratories working in regions where turnaround time can determine how quickly an outbreak response is mounted. The sequencing effort yielded complete F gene sequences for all thirteen selected samples and whole-genome sequences for three representative isolates. The whole-genome approach is particularly valuable for NDV because the virus genome, roughly 15,000 nucleotides in length, encodes six structural proteins and a small set of accessory proteins, and recombination or divergent ancestry in any genomic region can be missed when only the F gene is examined. By generating complete genomes from representative isolates and near-complete F gene coverage across the panel, the researchers maximized both breadth and depth of the dataset available for phylogenetic inference.

The sequence analysis revealed that the thirteen isolates were extremely closely related to one another, sharing 99.6 to 100 percent nucleotide identity across the regions sequenced. This homogeneity suggests a single introduction event into the affected operation, followed by clonal spread, rather than multiple independent introductions of distinct viruses. Every isolate harbored the canonical fusion protein cleavage site motif 112RRQKRF117, a polybasic amino acid sequence at positions 112 through 117 that is characteristic of virulent NDV strains. The cleavage site is the primary molecular determinant of pathogenicity in NDV: in virulent strains, the polybasic motif allows intracellular proteases such as furin to cleave the F0 precursor protein into its active F1 and F2 subunits in a wide range of host tissues, enabling systemic infection. Lentogenic, or low-virulence, strains lack this motif and can be cleaved only by proteases restricted to the respiratory and intestinal tracts, which limits their pathology. The presence of 112RRQKRF117 in all isolates therefore confirmed that the outbreak strain was velogenic, or highly virulent, at the molecular level.

Phylogenetic analyses based on both complete F gene sequences and whole-genome sequences placed all of the Peruvian isolates in class II of the NDV classification scheme, within genotype VII, and more precisely within subgenotype VII.1.1. Class II NDV encompasses the vast majority of characterized strains, including both vaccine strains and the virulent viruses responsible for most global epizootics, while class I contains predominantly avirulent aquatic bird viruses. Genotype VII has been the dominant virulent genotype circulating across Asia, Africa, the Middle East, and parts of Latin America since the late twentieth century, and subgenotype VII.1.1 has emerged in recent years as an important lineage in several countries. The placement of the 2025 southern Peruvian isolates within this subgenotype links the outbreak to a broader regional and international epidemiological context and underscores that the viruses driving disease in Peru belong to the same phylogenetic group that continues to circulate elsewhere.

A particularly significant finding of the study is that the 2025 viruses formed a well-supported, genetically homogeneous cluster that is distinct from previously reported Peruvian NDV strains. This separation is consistent with recent trends of local diversification, in which the virus lineage present in the country has accumulated unique mutations as it has circulated within Peruvian poultry populations over time. Such differentiation matters for practical reasons as well as evolutionary ones. Genotype VII viruses have a documented ability to escape immunity induced by some vaccines derived from genotype II strains, and the comparative protein analyses in this study reinforced that concern. When the researchers compared the fusion and hemagglutinin-neuraminidase proteins of the Peruvian isolates against genotype II reference strains, which include the classical vaccine lineages, they identified amino acid differences in both proteins. Because the hemagglutinin-neuraminidase protein facilitates receptor binding and neuraminidase activity and assists the fusion protein in mediating cell entry, substitutions in these surface glycoproteins can influence both antigenicity and viral fitness.

The implications of these amino acid differences extend to vaccination strategy and diagnostics. Hemagglutination inhibition testing, one of the most widely used serological tools in poultry medicine, depends on the interaction between the hemagglutinin-neuraminidase protein and antibodies raised against vaccine strains, so antigenic divergence between circulating field viruses and vaccine viruses can reduce the reliability of serological surveillance. Similarly, molecular assays designed around conserved regions must be periodically revalidated as locally circulating lineages diverge. The authors argue that their findings identify the virulent NDV VII.1.1 lineage as the direct cause of the 2025 outbreak and that routine genotyping should be incorporated into standard outbreak investigation protocols in the region. Without genotyping, an outbreak is simply diagnosed as Newcastle disease, with no information about which lineage is involved, whether it matches vaccine strains, or how it relates to viruses in neighboring production areas and countries.

Sustained genomic surveillance emerges from the study as the central recommendation for Peru and, by extension, for other countries where NDV data are sparse. The researchers note that recurrent outbreaks combined with limited genomic data have hindered understanding of the virus’s molecular epidemiology in Peru, and their work demonstrates how modern sequencing technology can close that gap. Nanopore sequencing of outbreak isolates delivered complete F gene sequences for a dozen isolates and whole genomes for three within a single investigation, at a cost and speed compatible with routine diagnostic workflows. The study was conducted on diagnostic samples collected exclusively from naturally dead or clinically affected birds submitted for laboratory testing, with no experimental infections performed, and all work with infectious material followed Peruvian biosafety regulations and World Organisation for Animal Health guidelines. The research was fully funded by FARVET SAC, and the authors declared no competing interests.

As NDV continues to evolve and as genotype VII lineages expand their geographic range, studies of this kind provide the foundational data on which national control programs depend. Knowing that a genetically homogeneous VII.1.1 virus caused the southern Peruvian outbreak allows veterinarians and regulators to assess whether existing vaccination programs are matching the field challenge, to trace potential transmission routes through the commercial poultry sector, and to establish a genomic baseline against which future isolates can be compared. The 99.6 to 100 percent identity among the 2025 isolates offers a snapshot of a single, tightly contained viral population, while the clear distinction from earlier Peruvian strains documents the ongoing evolutionary turnover of the virus in the country. Continued sampling, whole-genome sequencing, and phylogenetic monitoring will be required to determine whether this lineage persists, is replaced, or spreads beyond the region, and to ensure that the molecular epidemiology of Newcastle disease in South America is understood with the resolution needed to protect a poultry industry that feeds millions.

Subject of Research: Molecular characterization and phylogenetic analysis of virulent Newcastle disease virus subgenotype VII.1.1 from a 2025 poultry outbreak in southern Peru

Article Title: Whole-genome characterization and phylogenetic analysis of virulent Newcastle disease virus subgenotype VII.1.1 from a poultry outbreak in southern Peru

Article References: Villanueva-Pérez, D., Tataje-Lavanda, L., Montalván-Avalos, A., Montoya-Ortiz, S., Rios-Matos, D., Paredes-Inofuente, D., Ticona, J., Monasi, L., Cadillo-Kuroda, J., Jayo-Cucho, J., Goggín-Ortiz, J., Fernández-Sánchez, M., & Fernández-Díaz, M. (2026). Whole-genome characterization and phylogenetic analysis of virulent Newcastle disease virus subgenotype VII.1.1 from a poultry outbreak in southern Peru. Virology Journal. https://doi.org/10.1186/s12985-026-03319-7

Image Credits: AI Generated

DOI: 10.1186/s12985-026-03319-7

Keywords: Newcastle disease virus, subgenotype VII.1.1, whole-genome sequencing, fusion gene, phylogenetic analysis, poultry outbreak, Oxford Nanopore, Peru, virulence, genomic surveillance, virology, molecular epidemiology

The investigation was led by Reem M. Aljowaie, Ibrahim M. Aziz, Mohamed A. Farrag, Noorah A. Alkubaisi, Asma N. Alsaleh and Fahad N. Almajhdi of the Department of Botany and Microbiology at King Saud University. Between 2014 and 2020, the team collected 311 respiratory specimens from patients presenting with influenza-like illness in Riyadh. Each sample was screened by reverse transcription polymerase chain reaction, a molecular technique capable of detecting viral RNA with high sensitivity. Of the 311 specimens, 88, or 28.3 percent, tested positive for influenza A, while only six samples, representing 1.9 percent, were positive for influenza B virus. Although the number of influenza B detections was modest, the researchers sequenced the complete hemagglutinin and neuraminidase genes of these viruses, providing the full-length genetic data needed for rigorous evolutionary analysis.

Hemagglutinin and neuraminidase are the two surface proteins that define the antigenic identity of influenza viruses. Hemagglutinin mediates entry into host cells and is the principal target of neutralizing antibodies, while neuraminidase facilitates the release of newly formed viral particles. Mutations accumulating in these proteins can alter antigenic properties and, by extension, the degree of protection conferred by vaccination. The Riyadh team recorded mutations at both the nucleotide and amino acid levels, mapped N-linked glycosylation sites, and compared their sequences against WHO vaccine reference strains. They also generated six influenza B isolates from the 2014 to 2020 specimens and incorporated 31 previously published Riyadh sequences covering 2010 through 2025, allowing the analysis to extend across a decade and a half of local viral evolution.

The phylogenetic results revealed a clear lineage replacement event. Viruses belonging to the B/Yamagata lineage were detected in Riyadh in 2015, whereas samples from 2020 belonged exclusively to the B/Victoria lineage. Influenza B viruses are divided into these two genetically and antigenically distinct lineages, which co-circulated globally for decades before the B/Yamagata lineage dramatically declined after the COVID-19 pandemic. The Riyadh dataset mirrors this global pattern: among the sequenced isolates available for the full 2010 to 2025 period, no B/Yamagata-lineage viruses were detected in recent years, and sustained B/Victoria predominance was observed throughout the later portion of the surveillance window.

Within the B/Victoria lineage, the analysis showed that recent isolates from 2023 to 2025 carried the characteristic deletion of amino acids at positions 164 and 165 in the hemagglutinin protein. This deletion, located in or near antigenic regions of the protein, first emerged in globally circulating Victoria-lineage viruses and has become a defining feature of newer subclades. The Riyadh sequences from 2021 to 2025 all belonged to the V1A.3a.2 subclade, which has become the globally dominant form of B/Victoria. Earlier viruses in the dataset fell within subclades V1A.3 and related groups, illustrating the stepwise genetic drift that has characterized the lineage over the surveillance period.

Despite this ongoing evolution, the study found that the hemagglutinin and neuraminidase proteins of the circulating viruses were highly conserved relative to the WHO vaccine strains. Substitutions were identified in the major antigenic regions of hemagglutinin, including the 120-loop, the 150-loop, the 160-loop and the 190-helix, structural elements that antibodies recognize when they neutralize the virus. However, these changes were limited in number and did not translate into substantial genetic distance from the vaccine components. The B/Yamagata viruses from earlier years displayed lineage-specific glycosylation patterns, while the Victoria-lineage viruses maintained largely conserved N-linked glycosylation profiles, with one notable exception: some isolates showed a gain or loss of a glycosylation site at hemagglutinin position 197, a change that could potentially influence antigenicity and deserves continued monitoring.

Perhaps the most reassuring finding from a public health standpoint concerns vaccine compatibility. The researchers compared recent Riyadh isolates with the WHO-recommended vaccine strains B/Austria/1,359,417/2021 and B/Tokyo/EIS13-175/2025 and found that the local viruses remained genetically close to both, exhibiting only limited amino acid substitutions. This suggests that the influenza B component of seasonal vaccines has continued to match the viruses circulating in Riyadh, supporting the effectiveness of current vaccination strategies in the region. Because influenza B vaccine mismatch has historically contributed to reduced vaccine effectiveness in some seasons, this genetic concordance is a meaningful indicator for Saudi immunization planning.

The study also underscores the practical challenges of influenza B surveillance. With only 1.9 percent of the collected specimens testing positive for influenza B, the virus circulates at low levels in Riyadh compared with influenza A, and the number of sequences available for any given season is small. The authors are careful to frame their lineage replacement conclusion as reflecting the available surveillance dataset rather than an absolute claim of global or even national disappearance of B/Yamagata. Nevertheless, the finding aligns with international observations that B/Yamagata has not been robustly detected since around 2020, raising questions about whether the lineage may have gone extinct and whether quadrivalent vaccines, which include both B lineages, will continue to be necessary or whether trivalent formulations lacking B/Yamagata will become standard.

The research was approved by the Research Ethics Committee at King Saud University under Institutional Review Board number 14/4463/IRB 03/IRB, approved on December 3, 2014, and conducted in accordance with the Declaration of Helsinki, with informed consent obtained from all participants. The work was funded by the Ongoing Research Funding Program of King Saud University under grant ORF-2026-198. The authors declare no competing interests, and the article is published open access under a Creative Commons license.

For Saudi Arabia and the wider Middle East region, where long-term influenza B sequence data have historically been sparse, this fifteen-year record fills an important gap in the global map of influenza B evolution. The authors conclude that the predominance of B/Victoria and the non-detection of B/Yamagata within the available dataset underscore the need for continuous molecular surveillance to monitor viral evolution, assess vaccine strain compatibility, and support influenza prevention efforts in the kingdom. As influenza B continues its slow but steady genetic drift, sustained sequencing efforts in underrepresented regions such as Saudi Arabia will remain essential for ensuring that vaccine recommendations rest on a genuinely global picture of viral diversity.

Subject of Research: Long-term molecular epidemiology and genetic evolution of influenza B virus in Riyadh, Saudi Arabia, from 2010 to 2025

Article Title: Long-term molecular surveillance of influenza B virus in Riyadh, Saudi Arabia (2010–2025): lineage replacement, genetic evolution, and vaccine strain compatibility

Article References: Aljowaie, R. M., Aziz, I. M., Farrag, M. A., Alkubaisi, N. A., Alsaleh, A. N., & Almajhdi, F. N. (2026). Long-term molecular surveillance of influenza B virus in Riyadh, Saudi Arabia (2010–2025): lineage replacement, genetic evolution, and vaccine strain compatibility. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14442-9

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14442-9

Keywords: influenza B virus, B/Victoria lineage, B/Yamagata lineage, hemagglutinin, vaccine effectiveness, phylogenetic analysis, molecular epidemiology, lineage replacement, glycosylation, Saudi Arabia, viral evolution, surveillance

Entamoeba species are intestinal protozoa with a worldwide distribution, infecting humans and a broad range of animals. While some members of the genus, most famously Entamoeba histolytica, are responsible for amoebic dysentery and liver abscesses in people, others colonize the gut without causing obvious harm. Because these organisms are transmitted through fecally contaminated food and water, environments where humans and animals share space create ideal conditions for cross-species transmission. Non-human primates are of particular concern in this regard, since their physiological and genetic similarity to humans means that many of their parasites face relatively few barriers when jumping between hosts.

The research team, led by scientists at Anhui Science and Technology University, collected a total of 504 fecal samples from crab-eating macaques, also known as long-tailed macaques (Macaca fascicularis), housed at commercial breeding farms in two geographically distinct Chinese cities. Rather than relying on microscopy, which can confuse morphologically identical Entamoeba species, the researchers used polymerase chain reaction amplification and sequencing of the small subunit ribosomal RNA gene, a genetic marker that allows precise differentiation among six distinct Entamoeba species. This molecular approach is essential because species such as E. histolytica, E. dispar, and E. moshkovskii look identical under the microscope yet differ dramatically in their clinical significance.

The results revealed a layered picture of infection. Entamoeba coli was by far the most prevalent species, detected in 49.01 percent of samples, or 247 of the 504 specimens tested, with a 95 percent confidence interval spanning 44.6 to 53.4 percent. E. dispar followed at 36.51 percent, while E. histolytica, the most medically consequential species, was found in 8.13 percent of samples. The remaining species appeared at lower frequencies: E. chattoni at 5.95 percent, E. moshkovskii at 0.79 percent, and E. nuttalli at just 0.6 percent. The detection of E. histolytica in more than one in twelve animals is noteworthy, as this species remains a leading cause of parasitic death in humans globally.

Statistical analysis of the infection data uncovered a significant relationship between host age and the risk of carrying E. coli, with the association reaching a p-value below 0.0001. This strong age dependence suggests that older macaques accumulate infections over time, possibly through prolonged exposure to contaminated enclosures, changes in immune competence, or altered grooming and foraging behaviors. Understanding such risk factors is critical for breeding facilities, where managing parasite burden can affect animal welfare, the validity of biomedical research using these animals, and the safety of staff who work in close contact with the colonies.

The most striking findings emerged from the phylogenetic analysis. When the researchers reconstructed evolutionary relationships among the 247 E. coli isolates recovered from the macaques, they identified two distinct genotypes, designated SZ E. coli CEMs1 and SZ E. coli CEMs2. Both genotypes clustered firmly within the major E. coli clade and showed close genetic affinity with strains previously recovered from humans and other primate species. This pattern of shared lineages across host species is precisely what would be expected if the parasites are moving between humans and macaques, rather than evolving in isolated host-specific populations.

The presence of E. nuttalli, although rare in this cohort, adds another dimension to the zoonotic picture. This species, once confused with E. histolytica, is known to infect rhesus macaques and can cause liver abscesses in experimental animals, and previous studies have documented its genetic differentiation across macaque populations in Nepal, Myanmar, and China. Similarly, the detection of E. moshkovskii, an organism long considered a free-living amoeba but increasingly reported in human patients with diarrhea, underscores how fluid the boundaries between environmental, animal, and human Entamoeba lineages can be. The low prevalence of these species in the sampled colonies does not diminish their significance; rather, it highlights the value of sensitive molecular surveillance in detecting rare but potentially important infections.

From a practical standpoint, the findings carry implications for multiple stakeholders. For breeding facilities that supply macaques for biomedical research, high parasite prevalence complicates efforts to produce animals of defined health status, since subclinical infections can confound immunological and gastrointestinal studies. For public health authorities, the phylogenetic proximity of macaque-derived E. coli strains to human isolates argues for treating captive macaque colonies as potential zoonotic reservoirs warranting routine monitoring. And for the growing field of One Health, which examines the interconnected health of humans, animals, and environments, the study provides a concrete example of how intensively managed animal populations can harbor parasites with demonstrated potential for cross-host transmission.

The authors emphasize that enhanced surveillance is needed, both within breeding facilities and in contexts where macaques and humans interact more loosely, such as zoological gardens and areas where free-ranging macaques contact tourists. Prior studies of captive primates and their handlers in European zoos have already documented shared intestinal protists, suggesting that occupational exposure is a realistic concern. The Chinese breeding farms surveyed here represent a controlled setting, yet even under such conditions, nearly half the animals carried E. coli and a meaningful fraction harbored potentially pathogenic species, indicating that standard husbandry practices may not be sufficient to interrupt transmission cycles.

Looking forward, the genetic characterization of the two macaque E. coli genotypes opens avenues for finer-scale epidemiological work. Comparing these lineages with sequence data from human patients, livestock, and wild primates across Asia could clarify the directionality of transmission events and identify which host populations act as sources and which as sinks. Such work would build on a growing body of molecular epidemiology that has transformed Entamoeba from a morphologically defined genus into a genetically structured assemblage of species with distinct host associations and virulence potentials. As the new study demonstrates, even a parasite long regarded as a harmless commensal can reveal important truths about the porous boundaries between animal and human health, and about the responsibility that comes with keeping our closest relatives in close quarters.

Subject of Research: Zoonotic Entamoeba parasite prevalence and genetic diversity in captive crab-eating macaques in China

Article Title: Distribution of Zoonotic Entamoeba spp. in Crab-Eating Macaques Across China

Article References: Guo, Q., Gong, R., Ge, X., Li, M., Ma, J., Liu, X., & Li, W. (2026). Distribution of Zoonotic Entamoeba spp. in Crab-Eating Macaques Across China. Acta Parasitologica, 71(5), Article 216. https://doi.org/10.1007/s11686-026-01399-7

Image Credits: AI Generated

DOI: 10.1007/s11686-026-01399-7

Keywords: Entamoeba, crab-eating macaques, zoonotic parasites, E. histolytica, E. coli, E. dispar, SSU rRNA, phylogenetics, China, non-human primates, One Health, molecular epidemiology

The study, led by Taner Gürel of the Samsun Veterinary Control Institute together with Şinasi Umur of Ondokuz Mayıs University, set out to fill a gap in molecular epidemiological data for Turkish wild boar populations. Wild boars occupy a pivotal position in the sylvatic cycles of Sarcocystis, Toxoplasma gondii, and Neospora caninum, three cyst-forming parasites of the phylum Apicomplexa that infect both animals and, in some cases, humans. Because wild boar populations have expanded dramatically across Europe and Anatolia, and because their meat is increasingly consumed as game, understanding what parasites these animals carry has direct implications for food safety, veterinary medicine, and public health.

To detect the parasites, the team combined classical parasitological techniques with a battery of molecular assays. Muscle tissue samples were first subjected to artificial digestion, a method that liberates cysts from meat fibers, and to histopathological examination to look for the characteristic sarcocysts embedded in muscle. The researchers then deployed a multiplex polymerase chain reaction targeting the mitochondrial cytochrome c oxidase subunit I gene, known as cox1, alongside a conventional PCR targeting the 18S ribosomal RNA gene to identify and differentiate Sarcocystis species. For the other two parasites, they used species-specific PCRs: one amplifying the 529 base pair repetitive element of Toxoplasma gondii, a target prized for its sensitivity because it is repeated hundreds of times in the parasite genome, and another targeting the NC5 region of Neospora caninum.

The results were unambiguous for Sarcocystis. Sarcocystis miescheriana was detected in 92 percent of the sampled animals, making it by far the dominant species in the population. Notably, the zoonotic species Sarcocystis suihominis, which can infect humans who eat undercooked pork or wild boar meat, was not found in any of the samples. That absence is reassuring from a food safety standpoint, though the authors caution that continued surveillance is warranted. Phylogenetic analysis of the cox1 sequences obtained from the Turkish isolates placed them close to European strains of S. miescheriana, consistent with the picture of a parasite lineage circulating widely among wild suids across the continent. The 18S rRNA sequence generated in the study has been deposited in GenBank under accession number PV104359.

Co-infections emerged as a defining feature of the population. Fifty-six percent of the wild boars harbored at least two of the three parasite species, and 28 percent carried all three simultaneously. Such high rates of mixed infection reflect the overlapping transmission routes of these parasites: Sarcocystis miescheriana cycles between pigs and canids, with dogs and other carnivores shedding sporocysts that contaminate the environment and are ingested by intermediate hosts; Toxoplasma gondii is transmitted both through oocysts shed by cats and through tissue cysts in meat; and Neospora caninum, whose definitive hosts are canids, is a major cause of abortion in cattle. A wild boar foraging in a contaminated landscape can readily pick up all three pathogens over its lifetime.

To identify risk factors for infection, the researchers applied multivariable logistic regression adjusted for age and sex. Adult age emerged as a significant predictor of Toxoplasma gondii infection, with adult animals showing roughly 3.77 times the odds of infection compared with younger boars, a statistically significant association. A similar but non-significant trend was observed for Neospora caninum, with an adjusted odds ratio of 3.21. Sex was not a significant predictor for either parasite. Triple infections were numerically more common in older animals, a pattern consistent with cumulative environmental exposure over time, although this trend did not reach statistical significance. The age effect fits the biology of these parasites: animals that live longer encounter more contaminated soil, water, and prey, and once infected with tissue cyst-forming protozoa they typically remain infected for life.

The detection of Toxoplasma gondii DNA in half of the sampled boars carries particular public health weight. Toxoplasmosis is one of the most common zoonotic infections worldwide, and while healthy adults usually experience mild symptoms, the parasite can cause severe disease in immunocompromised individuals and in fetuses when a woman acquires a primary infection during pregnancy. Game meat is an increasingly recognized route of exposure, and cases of ocular toxoplasmosis following wild game consumption have been documented in the medical literature. The 529 base pair repetitive element sequences generated in this study have been deposited in GenBank under accession numbers PV133829 through PV133831, adding to the genetic record of the parasite in the region.

Neospora caninum, detected in 38 percent of the animals, is less often a direct human health concern but is economically significant in livestock. The parasite is a leading cause of abortion and neonatal mortality in cattle worldwide, and wildlife reservoirs are thought to contribute to its persistence and spread. Previous surveys in other countries have found antibodies against N. caninum in feral swine and non-carnivorous wildlife, and the Turkish study adds molecular confirmation of the parasite’s presence in wild boar tissues from the region. The finding reinforces the idea that wild boars, which share habitats with livestock and are scavenged upon or hunted by canids, participate in the epidemiology of a parasite that costs the dairy industry substantially each year.

The Turkish results align with a growing body of European literature. Molecular studies in Italy, Greece, Latvia, Iran, and China have repeatedly identified Sarcocystis miescheriana as the predominant Sarcocystis species in wild boars, and surveys in Switzerland have documented both Sarcocystis and Toxoplasma in muscles of wild boars destined for human consumption. What distinguishes the new study is its combined assessment of all three parasites in the same animals, its use of both multiplex and conventional PCR platforms, and its formal statistical modeling of age and sex as risk factors. By quantifying co-infection patterns rather than treating each parasite in isolation, the study offers a more realistic picture of the parasite ecology within a single wild population.

The authors conclude that their results update the molecular epidemiology of tissue cyst-forming apicomplexans in Turkish wild boars and reinforce the importance of sustained One Health surveillance at the wildlife-livestock-human interface. As wild boar numbers continue to grow and the popularity of game meat rises, the study serves as a reminder that hunters, processors, and consumers all have a stake in safe handling and thorough cooking of wild game. It also highlights the value of molecular tools, which can distinguish morphologically similar parasite species and reveal co-infections that microscopy alone would miss. For now, the wild boars of Türkiye’s Black Sea coast stand as a vivid example of how much invisible parasite traffic moves through a seemingly healthy wildlife population.

Subject of Research: Molecular prevalence, co-infections, and genetic characterization of Sarcocystis, Toxoplasma, and Neospora parasites in wild boars from Türkiye

Article Title: Molecular Occurrence, Co-infections and Genetic Characterization of Sarcocystis miescheriana, Toxoplasma gondii and Neospora caninum in Wild Boars (Sus scrofa) from Türkiye

Article References: Molecular Occurrence, Co-infections and Genetic Characterization of Sarcocystis miescheriana, Toxoplasma gondii and Neospora caninum in Wild Boars (Sus scrofa) from Türkiye. (n.d.). https://doi.org/10.1007/s11686-026-01397-9

Image Credits: AI Generated

DOI: 10.1007/s11686-026-01397-9

Keywords: Sarcocystis miescheriana, Toxoplasma gondii, Neospora caninum, wild boar, Türkiye, co-infection, molecular epidemiology, PCR, game meat, food safety, One Health, parasitology

The scale of the dataset is what gives the study its power. Whole genome sequencing was performed on nearly every culture-confirmed tuberculosis case in Hamburg across 25 years, allowing the researchers to compare the full genetic blueprints of bacterial strains rather than relying on older, lower-resolution fingerprinting methods. The team analyzed population structure and transmission dynamics in relation to patients’ self-reported geographical origins, combining genomic data with demographic and epidemiological information gathered through mandatory public health surveillance under Germany’s infectious diseases law. This integration of pathogen genetics with host demographics is precisely what earlier molecular epidemiological studies lacked, and it allowed the investigators to distinguish between bacteria that had merely been imported with their hosts and bacteria that were genuinely transmitting from person to person within the city.

The first major finding concerns lineage diversity. The Mycobacterium tuberculosis complex comprises several major lineages with distinct geographic footprints: Lineage 2 and Lineage 4 are highly transmissible, globally distributed generalists, while Lineages 1, 3 and 5 through 9 are geographically restricted specialists adapted to particular regions. In Hamburg, the researchers detected strains from lineages L1 through L6 as well as Mycobacterium bovis, the cattle-adapted member of the complex. Lineage 4 dominated throughout, accounting for 74.6 percent of all strains, or 2,337 isolates. But the composition of the bacterial population shifted markedly over time. In the first five years of the study, L4 strains made up 83.5 percent of isolates; in the final five years, that share had fallen to 63.0 percent. Over the same period, strains of Lineage 3, a specialist lineage classically associated with the Horn of Africa and South Asia, rose from 4.8 percent to 18.1 percent of the population.

That shift might seem to suggest that newly arrived lineages were outcompeting established ones, or that changing bacterial properties were driving the epidemiology. The genomic evidence says otherwise. When the researchers examined transmission clusters, groups of patients infected with nearly identical strains that indicate recent person-to-person spread, they found that the changing lineage distribution correlated with the increasing number of foreign-born patients rather than with enhanced transmission of any particular lineage. In other words, the diversification of Hamburg’s tuberculosis population was a demographic phenomenon, not a microbiological one. New strains arrived with new residents, but they did not, for the most part, go on to spread widely within the local population.

The cluster analysis drives this point home. Of the 269 transmission clusters identified across the 25-year period, 81 percent, or 218, were composed of Lineage 4 strains. This dominance was far out of proportion even to L4’s overall prevalence, indicating that sustained local transmission in Hamburg remained overwhelmingly the province of long-established bacterial lineages. Strains of specialist lineages such as L3, despite becoming numerically more common as imports increased, contributed relatively little to ongoing chains of transmission. The bacteria that thrive in Hamburg are, in an evolutionary sense, the bacteria that were already there.

Delving deeper into Lineage 4 revealed another layer of complexity: heterogeneity in transmission potential among its sublineages. Not all L4 strains are equal. The researchers found that sublineages L4.1.2.1, L4.8 and L4.3 were each detected in patients born in more than 15 different world regions, with more than 57 percent of those cases occurring in people from Europe. This pattern supports what evolutionary biologists call the generalist-specialist hypothesis at a finer resolution than ever before. Certain sublineages behave as globally successful generalists, capable of infecting and transmitting among host populations of vastly different genetic backgrounds and geographic origins, while others remain confined to specific regions. The importance of this sublineage-level resolution is a methodological lesson for the field: analyses that stop at the major-lineage level would miss the heterogeneity in transmissibility that the Hamburg data expose.

The technical machinery behind these conclusions deserves attention. Whole genome sequencing of more than 3,000 isolates allowed the team to apply a five-allele distance threshold, a conservative criterion under which strains sharing nearly identical core genomes are considered part of the same recent transmission chain. Core genome multilocus sequence typing and single nucleotide polymorphism analyses provided complementary views of population structure, and maximum likelihood phylogenetic methods placed the Hamburg strains within the global diversity of the tuberculosis complex. By combining these genomic tools with the patients’ self-reported regions and countries of birth, grouped according to United Nations statistical divisions, the researchers could ask, for any given cluster, whether it represented a single introduction with limited onward spread or sustained transmission across the community.

The public health implications are significant. In low-incidence settings, the central strategic question is whether each tuberculosis case is an isolated importation or part of an active local transmission network, because the two scenarios demand different responses. Imported cases call for ensuring that arriving populations have access to screening and care, while clustered cases call for contact investigation and outbreak response. The Hamburg study shows that genomic surveillance can make this distinction reliably at scale, and that the answer may not follow intuition. A rising share of foreign-born cases and a diversifying bacterial population did not translate into altered transmission dynamics; the city’s transmission landscape remained anchored in its established L4 sublineages. Policymakers worried that migration inherently fuels tuberculosis spread can point to this evidence that pathogen characteristics and local adaptation matter as much as host demographics.

The study also underscores the interplay between pathogen evolution and human population structure. Successful transmission, the authors conclude, is mediated by locally adapted sublineages, and the predominance of L4.1.2.1 and L4.8 among patients from a wide range of countries demonstrates that these sublineages have achieved a breadth of host adaptation that specialist lineages lack. Migration substantially increased the genetic diversity of the bacterial population in Hamburg but did not fundamentally alter how tuberculosis transmits there. As genomic sequencing becomes cheaper and more routine, the Hamburg experience offers a template for other low-incidence cities: maintain long-term, systematic sequencing integrated with demographic data, analyze at sublineage resolution, and interpret lineage shifts in light of migration patterns before attributing them to changes in bacterial fitness. Twenty-five years of genomes have turned a single German city into a natural laboratory for understanding how one of the world’s deadliest pathogens responds to the movement of its human hosts, and the answer, reassuringly, is that established local strains still hold the ground.

Subject of Research: Molecular epidemiology of Mycobacterium tuberculosis complex transmission and lineage diversity in relation to migration in Hamburg, Germany, over 25 years

Article Title: Migration and tuberculosis transmission in Hamburg, Germany: insights from 25 years of molecular epidemiology

Article References: Ullrich, N., Diel, R., Meywald-Walter, K., Schwarzbach, C., Gröschel, M. I., Kuhns, M., Friesen, I., Niemann, S., & Dreyer, V. (2026). Migration and tuberculosis transmission in Hamburg, Germany: insights from 25 years of molecular epidemiology. Genome Medicine. https://doi.org/10.1186/s13073-026-01750-7

Image Credits: AI Generated

DOI: 10.1186/s13073-026-01750-7

Keywords: tuberculosis, Mycobacterium tuberculosis complex, whole genome sequencing, molecular epidemiology, migration, lineage 4, transmission clusters, generalist-specialist hypothesis, genomic surveillance, Hamburg, low-incidence settings, sublineages

Orientia tsutsugamushi presents a formidable challenge to genomic analysis. Its genome is highly heterogeneous and repeat-rich, features that complicate both sequencing and assembly. For decades, molecular epidemiology of this bacterium has leaned on a small number of marker loci, short stretches of DNA assumed to serve as reliable proxies for the organism’s broader evolutionary relationships. The most widely used of these is tsa56, which encodes a major outer membrane antigen, alongside htrA and groEL, two more conserved housekeeping loci. Generations of genotype labels assigned to clinical and environmental isolates rest on sequences from these markers. Yet whether those labels correspond to true genome-wide relatedness had never been rigorously evaluated at scale.

The research team, led by Lele Zhao, Shiyu Li, and Shijie Chen, approached the question by assembling publicly available sequences of the three standard marker loci together with a set of 19 quality-controlled whole genomes. Their first test compared the two most widely used markers, tsa56 and htrA, across 35 isolates carrying both sequences. The phylogenetic trees built from these two markers were markedly incongruent. The Mantel correlation coefficient between the two distance matrices was just 0.103, with a P value of 0.433, indicating no statistically significant association. The normalized Robinson–Foulds distance, a measure of topological disagreement between phylogenetic trees, reached 0.938 on a scale where 1.0 represents complete discordance. In practical terms, the evolutionary picture painted by tsa56 bore almost no resemblance to the picture painted by htrA for the same set of isolates.

The team then evaluated whether any of the three marker loci could recover the topology of the core genome, the set of genes shared across all strains and therefore the best available proxy for the bacterium’s genuine vertical evolutionary history. None of the three markers succeeded. Normalized Robinson–Foulds distances between each marker tree and the core-genome tree ranged from 0.750 to 0.800, indicating substantial to severe topological discordance in every case. This result demonstrates that genotype assignments based on any single locus are strongly locus-dependent and cannot be considered directly interchangeable across markers. A strain labeled as one genotype according to tsa56 may occupy a very different position in the evolutionary tree when assessed with htrA or with genome-wide data.

Not all markers performed equally poorly, however. When the researchers examined whether marker-based pairwise distances correlated with genome-wide pairwise distances, the more conserved loci retained meaningful signal. The groEL marker produced a Mantel correlation coefficient of 0.845 with genome-wide distances, and htrA produced 0.613, both statistically significant at P less than 0.001. This means that although neither locus reproduces the core-genome tree faithfully, both carry usable information about how genetically distant strains are from one another. The tsa56 locus, by contrast, showed no significant correlation with genome-wide distance, producing a Mantel coefficient of just 0.146 with a P value of 0.313. For the most heavily used marker in scrub typhus molecular epidemiology, this is a sobering result. It suggests that tsa56, shaped perhaps by strong immune selection on the surface antigen it encodes, evolves in ways that decouple it from the rest of the genome.

The study also compared two different genome-scale approaches: a phylogeny built from core-genome single nucleotide polymorphisms and one built from core proteins. These showed a significant positive correlation in their distance matrices, with a Mantel coefficient of 0.625 and P less than 0.001, yet their topologies still differed, with a normalized Robinson–Foulds distance of 0.500. Even at the whole-genome level, nucleotide-based and protein-based reconstructions of Orientia’s evolution tell partially different stories, a reminder that analytical choices matter even when the data are rich.

Beyond the marker comparison, the team conducted a pan-genome analysis, cataloging the full repertoire of genes present across the sampled strains. They identified 4,350 gene clusters in total, of which only 13.8 percent constituted the core genome, meaning genes present in every strain. The remaining vast majority were accessory genes, present in some strains but not others, or strain-specific genes found in only a single isolate. The pan-genome accumulation curve remained open, rising steadily as more genomes were added without approaching a plateau. An open pan-genome indicates that the gene repertoire of Orientia tsutsugamushi is far from fully sampled and that each newly sequenced strain is likely to carry previously unseen genes. This pattern is typical of bacterial species with extensive horizontal gene transfer and recombination, and it underscores how much of this pathogen’s genetic repertoire remains undiscovered.

A striking feature of the pan-genome is how little of it can be functionally annotated. Most accessory genes, 60.1 percent, and an even larger proportion of strain-specific genes, 81.3 percent, were uncharacterized, meaning that no known function could be assigned to them. These genes of unknown function may include determinants of virulence, host adaptation, or antibiotic tolerance, but their roles remain speculative until functional studies catch up with the genomic data. The open, accessory-dominated structure of the pan-genome suggests that Orientia’s evolutionary success as a pathogen may depend heavily on this unexplored genetic reservoir.

The researchers also tested whether accessory gene composition correlated with either the geographic origin of the strains or their core-genome lineages. Despite the high heterogeneity of accessory-gene repertoires across isolates, no statistically detectable structuring by geography or core lineage emerged in the dataset. This absence of association suggests that horizontal gene transfer reshapes the accessory genome largely independently of the vertical evolutionary history recorded in the core genome and independently of where strains circulate. In other words, two strains isolated from the same region or belonging to the same core lineage may carry substantially different accessory gene sets, while distant strains may share accessory genes acquired through recombination.

The findings carry immediate practical implications. Genotype labels and strain relationships derived from single markers should be interpreted strictly within a locus-specific framework and should not be treated as interchangeable across loci, the authors conclude. In the small matched genome sets available, groEL and htrA better reflected genome-wide pairwise distances than tsa56, offering a hierarchy of marker reliability for situations where whole-genome sequencing is not feasible. More broadly, the study provides a curated overview of Orientia tsutsugamushi diversity in public datasets and a reproducible analytical framework for future surveillance. As scrub typhus continues to expand its recognized geographic range and as whole-genome sequencing becomes more accessible, this work lays the groundwork for a transition from marker-based classification toward genome-informed epidemiology, an essential step toward improved diagnostics, vaccine design, and therapeutic strategies against this neglected but dangerous pathogen.

Subject of Research: Genome-scale analysis of genetic diversity and pan-genome architecture in the scrub typhus bacterium Orientia tsutsugamushi

Article Title: Genome-scale insights into the genetic diversity and pan-genome architecture of Orientia tsutsugamushi

Article References: Zhao, L., Li, S., Chen, S., Liu, J., Li, R., Yu, Z., Yang, F., Shao, Z., Liu, K., & Lu, Z. (2026). Genome-scale insights into the genetic diversity and pan-genome architecture of Orientia tsutsugamushi. BMC Genomics. https://doi.org/10.1186/s12864-026-13351-0

Image Credits: AI Generated

DOI: 10.1186/s12864-026-13351-0

Keywords: Orientia tsutsugamushi, scrub typhus, pan-genome, genetic diversity, molecular epidemiology, phylogenetic discordance, tsa56, groEL, htrA, accessory genes, genomic surveillance, core genome

The scale of the 2026 cyclosporiasis season has sharpened the urgency of that argument. According to surveillance data from the Centers for Disease Control and Prevention updated on September 1, 2026, 18,445 laboratory-confirmed domestically acquired cases were reported across 49 states and the District of Columbia between May 1 and August 31. Those infections resulted in 990 hospitalizations and two deaths, a dramatic escalation from the 1,180 cases recorded during the comparable period in 2025. Affected individuals reported no international travel during the 14 days preceding illness onset, which supports domestic foodborne exposure as the principal source of infection. As of September 3, 2026, a single outbreak cluster alone had caused 11,458 confirmed illnesses, 495 hospitalizations, and two deaths across 20 states, yet investigators emphasize that this cluster does not account for the entire national increase. The CDC and the U.S. Food and Drug Administration are continuing to investigate additional clusters for which contaminated food sources have not yet been pinpointed.

Understanding why cyclosporiasis is so difficult to control requires an appreciation of the unique biology of its causative agent, the single-celled parasite Cyclospora cayetanensis. Unlike many bacterial foodborne pathogens, Cyclospora is not transmitted directly from person to person because the parasite must spend several days to weeks in the environment before its oocysts sporulate and become infectious. Human infections therefore occur almost exclusively through ingestion of food or water contaminated with fully mature oocysts derived from human fecal waste. Contamination frequently takes place during agricultural production, through inadequately treated irrigation water, contaminated wash water, poor sanitation facilities for farm workers, or improper handling during harvesting, packaging, and processing. This environmental maturation requirement means that the parasite effectively travels through a hidden ecological reservoir before it ever reaches a consumer, which is precisely the gap that conventional human-centered surveillance cannot see into.

Over the past decade, the CDC, in collaboration with state health departments and the FDA, has significantly strengthened national cyclosporiasis surveillance through mandatory disease reporting, improved laboratory diagnostics, enhanced molecular epidemiology, and coordinated multistate outbreak investigations. These improvements have measurably increased the capacity to detect outbreaks and to monitor seasonal trends. Nevertheless, the current framework remains predominantly reactive in structure. Public health action generally begins only after infected individuals develop symptoms, seek healthcare, receive laboratory confirmation, and are linked to one another through time-consuming epidemiological investigations. While these approaches are essential for outbreak response, they provide limited opportunity to prevent transmission before contaminated food reaches consumers. Consequently, interventions such as recalls and public advisories often arrive only after substantial community exposure has already occurred, a pattern repeatedly observed during fresh-produce-associated outbreaks of the past several years.

The core of the proposed solution is food supply chain surveillance, an integrated strategy that exploits the digitalization of modern food distribution. Contemporary supply networks transport fresh produce across multiple states within a matter of days, which makes rapid traceback investigations essential during an outbreak. Emerging technologies such as blockchain-enabled traceability, digital supply chain management platforms, radio-frequency identification systems, and electronic shipment records now provide unprecedented opportunities to monitor the movement of produce from farms through processing facilities, distribution centers, retailers, restaurants, and ultimately to consumers. The researchers argue that integrating these traceability systems directly with epidemiological surveillance databases would allow investigators to reconstruct distribution pathways within hours rather than weeks, substantially reducing the time required to identify contaminated food sources, issue targeted recalls, and remove hazardous product from commerce before further exposures accumulate.

Clinical surveillance itself also requires modernization to improve the speed and sensitivity of outbreak detection. The authors call for electronic laboratory reporting to be seamlessly integrated with hospital electronic health records and state surveillance systems, enabling immediate notification of confirmed cyclosporiasis cases rather than delayed batch reporting. Syndromic surveillance systems capable of monitoring upticks in acute diarrheal illness could provide additional early warning signals before laboratory confirmation becomes available, since Cyclospora diagnosis often lags symptom onset by days or weeks. Coupling these systems with automated statistical anomaly-detection algorithms would allow public health authorities to recognize unusual disease clusters earlier and to initiate investigations before outbreaks expand across multiple jurisdictions, converting surveillance from a historical record into a genuine forecasting tool.

Molecular epidemiology is positioned as a central pillar of future cyclosporiasis surveillance. Genetic characterization of Cyclospora cayetanensis has historically been constrained by technical limitations and by the parasite’s relatively low genetic diversity, which has made it difficult to confidently link cases from different geographic areas or to distinguish outbreak-associated strains from background sporadic infections. Recent advances in molecular biology are changing that calculus. Whole-genome sequencing, multilocus sequence typing, targeted amplicon sequencing, and metagenomic approaches now have the potential to discriminate outbreak-associated strains from unrelated infections with increasing precision. When genomic data are combined with epidemiological and supply chain information, investigators gain a triangulated picture of an outbreak that can withstand the scrutiny required for regulatory action, and genomic signatures recovered from environmental and food samples can potentially be matched to clinical isolates to confirm contamination routes.

Effective implementation of a One Health surveillance framework will, however, demand unprecedented collaboration among professions and agencies that historically operate in separate silos: clinicians, epidemiologists, microbiologists, environmental scientists, agricultural specialists, food safety regulators, veterinarians, and policymakers. One of the greatest barriers to effective outbreak response remains the fragmentation of surveillance data across multiple agencies with limited interoperability. Clinical reports, laboratory findings, environmental monitoring results, genomic sequencing data, and food traceability information currently reside in disconnected systems governed by different jurisdictions and data standards. Establishing standardized national data-sharing platforms capable of integrating all of these data streams would significantly improve coordination among federal, state, and local agencies while accelerating outbreak investigations and public health decision-making. The One Health framing also extends the surveillance gaze upstream to the agricultural and environmental conditions—irrigation water quality, worker sanitation, and wildlife or wastewater contributions—that seed contamination in the first place, offering points of intervention that purely clinical systems cannot reach.

The 2026 outbreak season serves as a stark demonstration of what is at stake. A more than fifteen-fold increase in reported cases compared with the same months of the previous year, nearly a thousand hospitalizations, and two deaths occurred despite an established notifiable-disease infrastructure and experienced investigative teams at federal and state agencies. The authors contend that these outcomes are not evidence that surveillance personnel failed, but evidence that a fundamentally reactive architecture cannot keep pace with a pathogen embedded in a vast, fast-moving, and complex food production and distribution network. Their proposal reframes cyclosporiasis control as a systems problem spanning human clinical medicine, environmental science, agricultural practice, genomics, and information technology. If adopted, an integrated One Health surveillance system would aim to detect contamination signals in the environment or the supply chain before consumers are exposed, shrinking outbreak response from a matter of weeks to a matter of hours and converting a recurring public health burden into a largely preventable event.

Subject of Research: Integrated One Health surveillance for foodborne cyclosporiasis outbreaks in the United States

Article Title: An integrated One Health surveillance on cyclosporiasis outbreaks in the United States

Article References: Aborode, A. T., Allison, M. O., Akinyosoye, F. O., & Aliyu, A. A. (2026). An integrated One Health surveillance on cyclosporiasis outbreaks in the United States. New Microbes and New Infections, 73, Article 101851. https://doi.org/10.1016/j.nmni.2026.101851

Image Credits: AI Generated

DOI: 10.1016/j.nmni.2026.101851

Keywords: cyclosporiasis, Cyclospora cayetanensis, One Health, foodborne disease, surveillance, CDC, outbreak investigation, molecular epidemiology, food supply chain, whole-genome sequencing, public health, fresh produce safety

The Democratic Republic of Congo carries a high burden of chronic hepatitis B, a condition that can progress silently over decades toward cirrhosis and hepatocellular carcinoma. Yet despite this substantial disease burden, the molecular characteristics of the virus circulating in the country had remained poorly defined. That gap matters for reasons that extend far beyond academic curiosity. The genotype of hepatitis B virus infecting a patient can influence the natural history of infection, the performance of diagnostic assays, the likelihood of antiviral resistance, and the effectiveness of vaccination strategies. Without a clear picture of viral diversity, surveillance systems, clinicians, and elimination programs are working with an incomplete map.

To address that gap, the researchers followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 guidelines, systematically searching publicly available databases for studies reporting molecular characteristics of hepatitis B virus isolated in the Democratic Republic of Congo. The quality of each eligible study was assessed using the Newcastle-Ottawa Scale, a standard instrument for appraising observational research. From the screened literature, eight studies published up to April 2026 met the inclusion criteria, together contributing 273 hepatitis B virus sequences collected between 2000 and 2023. The team extracted data on genotypes, subgenotypes, recombinant strains, antiviral resistance-associated mutations, and immune or vaccine escape mutations, then synthesized the findings quantitatively.

The headline result concerns genotype distribution. Genotype E accounted for the largest share of reported sequences at 53.8 percent, followed closely by genotype A at 43.6 percent, with genotype D making up the remaining 2.2 percent. That near-even split between two major genotypes is itself noteworthy, because many countries in the region are dominated by a single genotype, most commonly genotype E in West and Central Africa. More striking still, the researchers found that the distribution of genotypes varied significantly across geographic regions of the country, a statistically robust pattern with a p value below 0.001. Such regional heterogeneity hints at distinct historical transmission chains and migration dynamics shaping the epidemic in different parts of this vast nation.

Perhaps the most biologically intriguing finding lies within genotype A. Far from representing a homogeneous viral population, genotype A in the Democratic Republic of Congo exhibited considerable genetic diversity, encompassing subgenotypes A1 through A4, the more recently described subgenotype A8, quasi-A3 variants, unclassified subgenotype A* variants, and A/E recombinant strains. This depth of diversity suggests that multiple evolutionary lineages of the virus have circulated within the country, likely reflecting a long and complex history of introduction and local evolution. Recombinant strains, in which genetic material from different genotypes has been exchanged during mixed infections, are of particular interest to virologists because recombination can alter antigenic properties and complicate genotype-based diagnostic algorithms.

The review also identified mutations with direct clinical relevance. Antiviral resistance-associated substitutions, typically arising in the reverse transcriptase domain of the viral polymerase under selective pressure from drugs such as lamivudine or adefovir, were present in 6.7 percent of the reported sequences. Meanwhile, immune- and vaccine-escape substitutions, which alter surface antigen epitopes targeted by antibodies generated through natural infection or vaccination, were detected in 9.5 percent of isolates. Neither figure is alarmingly high in absolute terms, but both indicate that variants with potential implications for treatment response and vaccine effectiveness are already circulating within the population. In a country where diagnostic capacity varies widely, the presence of surface gene mutations raises practical questions about whether routine rapid diagnostic tests and enzyme-linked or chemiluminescent immunoassays reliably detect all circulating viral variants.

These findings arrive at a consequential moment. The World Health Organization has set ambitious targets for eliminating viral hepatitis as a public health threat, and national elimination strategies depend on accurate knowledge of which viral variants are circulating where. For the Democratic Republic of Congo, the review exposes critical gaps in molecular surveillance. With only eight studies and 273 sequences available for a country of its size and population, the available data represent a sparse sampling of the epidemic. The authors emphasize that the substantial genetic diversity and marked geographic variation they document limit the reliability of national-level summary estimates and argue that strengthening nationwide genomic monitoring will be essential to inform targeted prevention, optimize treatment strategies, and support progress toward elimination.

The technical underpinnings of the review are worth appreciating. Genotyping of hepatitis B virus conventionally relies on sequencing regions of the viral genome, most often the surface and polymerase genes, and comparing them against reference sequences. Subgenotype assignment demands higher-resolution analysis, and the identification of recombinant forms requires bootscanning or similar phylogenetic methods capable of detecting mosaic genomes. That such varied lineages were recoverable even from a limited dataset suggests that expanded sequencing efforts in the country would likely uncover additional diversity. It also underscores the value of depositing sequence data in publicly accessible databases, since the entire synthesis was built from studies whose molecular data were openly available.

For clinicians and public health authorities in the Democratic Republic of Congo and neighboring countries, the practical implications are tangible. High genotype diversity means that treatments and diagnostic tools validated primarily against other viral populations may behave differently in Congolese patients. The detection of vaccine-escape mutations, while preliminary, argues for sustained post-vaccination serological monitoring, particularly among infants vaccinated under the national program. The presence of polymerase resistance mutations supports the judicious use of antiviral therapy with appropriate monitoring, and it reinforces the case for tenofovir-based first-line regimens, which carry a higher genetic barrier to resistance than older nucleoside analogues. Regional variation in genotype distribution further suggests that surveillance and response efforts may need to be tailored at the provincial level rather than designed around a single national profile.

The study, conducted without external funding by a small team in Mbujimayi, also demonstrates the growing capacity of African researchers to synthesize continental evidence and direct attention to understudied epidemics. As genomic sequencing becomes cheaper and more accessible, the hope is that the picture sketched by this review will be repeatedly refined, with denser sampling across all provinces and over time. Until then, the message to policymakers is clear: hepatitis B in the Democratic Republic of Congo is not a single epidemic but a mosaic of genetically distinct viral populations, and eliminating it will require surveillance infrastructure capable of seeing that mosaic in full.

Subject of Research: Molecular epidemiology and genetic diversity of hepatitis B virus in the Democratic Republic of Congo

Article Title: Molecular characterization of hepatitis B virus in the Democratic Republic of Congo: a systematic review

Article References: Cindibu Kalonji, F., & Tshibangu-Kabamba, E. (2026). Molecular characterization of hepatitis B virus in the Democratic Republic of Congo: a systematic review. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14433-w

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14433-w

Keywords: hepatitis B virus, Democratic Republic of Congo, molecular epidemiology, genotype E, genotype A, systematic review, vaccine escape mutations, antiviral resistance, viral recombination, genomic surveillance, BMC Infectious Diseases, viral hepatitis