The study, published in Frontiers in Aquaculture, is the first to describe detailed surveillance using multiple sample matrices from fish in an ISA outbreak in a fully immunized population. Over more than a year, fish health experts visited the farm twice a month, and researchers collected samples from 2,821 fish at the sea site and another 840 at the slaughterhouse. The team analyzed swabs from skin and gills, heart and kidney tissues, blood for hematocrit measurements, and even water from the cages and from well boats used during delicing operations. The goal was to understand how the virus behaves in vaccinated fish under real field conditions, where the infection is not the only disease pressure and where husbandry stressors such as sea lice treatments shape the biological landscape.

The virus itself belongs to the family Orthomyxoviridae, the same family as influenza viruses, and exists in two phenotypic variants defined by the highly polymorphic region of gene segment 6. The non-pathogenic form, ISAV HPR0, circulates widely in Norwegian farmed salmon and is considered a benign resident of the production environment. The pathogenic form, ISAV HPRΔ, arises when HPR0 undergoes a deletion in the HPR combined with a mutation or insertion in the cleavage site of gene segment 5, transforming a quiet passenger into a killer. Primary outbreaks occur when this transition happens, and secondary outbreaks can then spread to nearby farms through live fish movements, vessel traffic, or passive transport in water currents. ISA was first detected in Norway in 1984 and peaked at 80 annual outbreaks in 1990 before biosecurity measures introduced between 1989 and 1991 brought the number down to between 10 and 25 outbreaks per year over the last decade.

At the Salangslia site, the fish had been vaccinated with a formulation containing the European ISAV genotype along with antigens against infectious pancreatic necrosis virus and several bacterial pathogens. According to the vaccine leaflet, immunity develops within 500 degree-days and lasts at least 7 months after vaccination, and vaccinated fish typically show reduced or absent clinical signs. However, they can still be infected, shed virus, and become asymptomatic carriers. The 754,825 Atlantic salmon transferred to seawater in May 2021 weighed approximately 270 grams each and were distributed across seven cages. Notably, the population had undergone an unusually rigorous sorting process at the hatchery, with approximately 150,000 smolts of inferior quality culled using a grading grid, meaning only 85 percent of the original fish were considered robust enough for seawater transfer.

The results paint a picture of a virus that persisted at low levels for months before becoming more detectable late in the production cycle. Of the 2,821 fish sampled at the sea site, 128 tested positive for ISAV by real-time RT-PCR. Only one of these detections, from a gill swab in November 2021, was confirmed as the non-pathogenic HPR0 variant; the rest were sequenced as HPRΔ. The number of positive individuals increased sharply from April 2022 onward, with the majority of detections occurring in cages that had tested positive at the start of the study and were located nearest to shore. By the end of the production cycle, ISAV HPRΔ had been detected in fish from all seven cages, up from four cages at the time of initial confirmation. Yet only five fish met the full Norwegian diagnostic criteria for clinical ISA, which require virus detection by PCR plus compatible histopathology and immunohistochemistry.

One of the most striking findings concerns the choice of sample matrix. Heart and kidney tissues are the recommended samples for ISAV detection under international standards, but the researchers found that skin swabs outperformed both heart tissue and gill swabs by a wide margin. Among the 128 ISAV-positive fish, skin swabs detected the virus in 73 percent of cases, gill swabs in 41 percent, and heart tissue in only 25 percent. The differences were statistically significant across all pairwise comparisons. Because swab samples likely reflect viral shedding through skin and mucosal surfaces rather than the infection status of individual fish, the authors suggest they may be particularly useful for early detection and non-lethal monitoring at the farm level. Any positive swab result would still need to be followed up with tissue sampling to confirm disease according to established criteria, but the finding points toward surveillance strategies that reduce the need to sacrifice healthy fish.

The study also identified hydropericardium, an accumulation of fluid in the sac surrounding the heart, as a highly specific predictor of ISA in moribund fish. Among 952 moribund fish with autopsy findings, only 13 showed hydropericardium, but the association with ISAV HPRΔ detection in heart tissue was dramatic, with an odds ratio of 51.7. Other autopsy findings such as skin ulcers, pale organs, and dark liver showed no significant association with viral detection. Anemia, traditionally considered a hallmark of ISA, was actually associated with lower odds of detecting the virus, likely because low hematocrit values in this population were driven by other conditions, including bacterial ulcers and mechanical injuries from delicing treatments, rather than by the virus itself.

The disease situation at the farm was complicated by a suite of other pathogens. Heart and skeletal muscle inflammation, parvicapsulosis, epitheliocystis, winter ulcers caused by Moritella viscosa, bacterial gill inflammation, and costiasis were all diagnosed during the study period. The site operated under a green aquaculture license requiring adult female sea lice levels below 0.25 per fish per cage, which necessitated seven thermal delicing treatments during the study period, well above the average of 3.82 treatments at 11 nearby farms. These treatments, while effective against lice, cause handling stress and mechanical injuries that can compromise fish health. Cumulative mortality reached 10.04 percent over the production cycle, but the researchers attribute this primarily to production-related factors rather than to ISA itself.

Environmental nucleic acid analysis, using water samples filtered through charged membranes to concentrate viral particles, yielded mixed results. Of 364 water samples collected at the farm, 98 tested positive for ISAV, but only 20 could be sequenced, and nearly all were the non-pathogenic HPR0 variant. Just one water sample, collected from a cage being emptied at the end of the study, contained HPRΔ. The authors suggest that virus shedding from this vaccinated population was low, or that viral particles were dispersed below detectable levels in the open sea cages. Water samples from well boats during delicing operations were more frequently positive, hinting that semi-enclosed systems where fish are concentrated may offer better opportunities for environmental surveillance than open cages.

The researchers acknowledge that the study design, conducted during a normal production cycle at a commercial farm, did not include a non-vaccinated control group, making it impossible to directly assess vaccine efficacy. The extensive pretransfer sorting of smolts, which is not standard industry practice, may also have reduced the observed prevalence of ISAV-positive fish. Nevertheless, the low number of clinically confirmed ISA cases despite widespread viral detection is consistent with a potential mitigating effect of vaccination, particularly in the earlier phases of production. The increase in viral detections toward the end of the cycle suggests that vaccine-induced immunity may have waned or been overwhelmed by the cumulative stress of delicing treatments and co-infections. The authors conclude that rigorous surveillance, particularly swabbing of moribund fish for early detection, combined with robust biosecurity measures remains critical for managing ISA risk, and that non-lethal sampling strategies aligned with the principles of replacement, reduction, and refinement in animal research deserve a central place in future disease control programs.

Subject of Research: Infection dynamics and surveillance of infectious salmon anemia virus in vaccinated Atlantic salmon under field conditions

Article Title: Infectious salmon anemia in vaccinated Atlantic salmon: a field case study

Article References: Patel, S. J., Dale, O. B., Fjellsøy, K. R., Bekkeli, K. E., Breck, O., Bendiktsen, R., Bornø, G., Brun, E., Jørgensen, L. G., Hellberg, H., Larsen, S., Kvalvik, H., & Moldal, T. (2026). Infectious salmon anemia in vaccinated Atlantic salmon: a field case study. Frontiers in Aquaculture, 5, Article 1885657. https://doi.org/10.3389/faquc.2026.1885657

Image Credits: AI Generated

DOI: 10.3389/faquc.2026.1885657

Keywords: infectious salmon anemia, ISAV, Atlantic salmon, aquaculture, vaccination, fish health surveillance, PCR detection, skin swabs, hydropericardium, environmental nucleic acid, sea lice treatments, Norwegian Veterinary Institute

The research team, led by Huan Li and Lei Ma of Hebei Normal University together with Jing Huang of Hebei Children’s Hospital, assembled an unusually large sample set for this kind of survey: 2,448 human fecal specimens and 215 ticks of the species Haemaphysalis longicornis, an aggressive, wide-ranging biting tick common across East Asia. Using polymerase chain reaction assays designed to amplify the 18S rRNA gene, a standard molecular marker for identifying eukaryotic microorganisms, the researchers screened every sample for Colpodella DNA. The 18S rRNA gene is favored in studies of protist diversity because it is present in all eukaryotes, contains both conserved and variable regions, and allows newly recovered sequences to be compared against a deep archive of reference sequences from known organisms.

The results were striking in their consistency across the two very different sample types. Colpodella DNA was detected in 136 of the human fecal samples, a detection rate of 5.56 percent, and in 11 of the tick samples, a rate of 5.12 percent. The near-identical prevalence in feces and ticks is one of the more intriguing aspects of the study, hinting at some shared route of exposure or a common environmental reservoir linking the human and tick samples, though the design of the study cannot distinguish among the many possible explanations, including ingestion of contaminated food or water, environmental pass-through, or a genuine biological association with the tick vector.

Every PCR-positive sample yielded a high-quality 18S rRNA sequence when the amplified DNA was read by Sanger sequencing, a validation step that strengthens confidence in the specificity of the detection. Because some of the tick-derived sequences were identical to one another, the researchers collapsed the data into representative sequence types, ultimately selecting one tick-derived sequence and 21 distinct human-derived sequence types for deeper analysis. These 22 representative sequences were deposited in GenBank under accession numbers QB017305 through QB017326, making them available to other researchers for comparison and future surveillance work.

Phylogenetic analysis, the technique biologists use to place newly recovered gene sequences on the tree of life, showed that all 22 representative sequences from the study clustered within previously reported Colpodella lineages. In other words, the DNA found in human stool and ticks belongs to the same evolutionary neighborhood as Colpodella species that have been described from aquatic and terrestrial habitats around the world. The sequences did not branch off into entirely novel territory, which suggests that the organisms detected in Hebei are related to known forms rather than representing a radically divergent new lineage, although species-level identification in this group remains difficult because morphology and molecular data do not always align neatly.

To probe the genetic variation within their dataset, the team performed a haplotype analysis, a method that groups sequences by their shared sets of variable sites. Among the analyzed sequences, they identified three haplotypes, indicating a modest but real degree of genetic diversity among the Colpodella organisms whose DNA was recovered from the samples. Haplotype networks and diversity statistics are standard tools in population genetics, and applying them to environmental protist DNA can reveal whether a detection reflects a single widespread genotype or a mixture of related strains circulating in the environment. In this case, the limited number of haplotypes suggests relatively constrained diversity in the sampled region, though the authors caution that broader sampling would be needed to draw firmer conclusions.

Understanding why this matters requires a short detour into evolutionary biology. Colpodella species are predatory flagellates that feed by a process called myzocytosis, in which they attach to another microbe, puncture its membrane, and suck out its cytoplasmic contents. This dramatic feeding strategy has fascinated cell biologists in part because it may resemble the evolutionary steps that gave rise to intracellular parasitism. Colpodellids are considered the free-living sister group to the Apicomplexa, the phylum that includes Plasmodium, the malaria parasite, and Toxoplasma gondii. Studying Colpodella therefore offers a window into how some of humanity’s most burdensome parasites may have evolved from free-living ancestors that once hunted their prey from the outside.

The new study also fits into a rapidly expanding literature on where Colpodella DNA shows up outside of ponds and soil. Recent surveys have reported the organism’s genetic traces in goats, foxes, and birds; in Hyalomma ticks infesting camels in Egypt; in ticks feeding on ruminants in Italy; in horses; in zoo animals; and even in the urine of a human patient. Clinically, isolated case reports have described Colpodella-like parasites in a woman in China and in a patient with neurological symptoms whose infection was linked to a potential novel tick-borne Colpodella species. A 2025 scoping review of the genus’s biological characteristics and zoonotic potential underscored how much remains unknown about whether these detections represent transient environmental exposure, colonization, or true infection.

That uncertainty is central to how the Hebei findings should be interpreted, and the authors are explicit about the limits of their method. PCR-based detection confirms only that Colpodella DNA was present in the sample; it cannot determine whether live organisms were present, whether they were actively replicating, whether they colonized the human gut or the tick, or whether they caused any disease. DNA can persist after an organism has died, and environmental contamination or passive passage through the body can both produce positive signals. Distinguishing among these possibilities will require complementary approaches, including attempts to culture the organisms, sequencing of additional genetic markers beyond the 18S rRNA gene, and biological studies of how Colpodella interacts with animal hosts.

Nevertheless, the study marks a meaningful addition to surveillance data on an understudied group of protists. The large number of human samples screened, the near-matching detection rates in feces and ticks, the successful sequencing of every positive sample, and the public deposition of 22 representative sequences collectively provide a foundation for future work. As molecular surveys continue to sweep ever more environments and host species, Colpodella keeps appearing in unexpected places, and each new detection sharpens the questions that make this genus scientifically compelling: how these predatory relatives of apicomplexan parasites move between environmental reservoirs, animals, and occasionally people, and whether any of them pose a genuine health risk. For now, the answer in Hebei Province is a well-documented molecular presence and a clear agenda for the research that must follow.

Subject of Research: Molecular detection and genetic diversity of Colpodella protist DNA in human fecal and tick samples in China

Article Title: Molecular Detection and Genetic Characterization of Colpodella spp. DNA in Human Fecal and Tick Samples from Hebei Province, China

Article References: Li, H., Huang, J., Zhang, M., Zhang, Y., Chen, Y., & Ma, L. (2026). Molecular Detection and Genetic Characterization of Colpodella spp. DNA in Human Fecal and Tick Samples from Hebei Province, China. Acta Parasitologica, 71(5), Article 234. https://doi.org/10.1007/s11686-026-01419-6

Image Credits: AI Generated

DOI: 10.1007/s11686-026-01419-6

Keywords: Colpodella, protists, Apicomplexa, Haemaphysalis longicornis, ticks, 18S rRNA, PCR detection, genetic diversity, haplotypes, Hebei Province, zoonotic potential, myzocytosis

The research team, led by Shahida Kashif of Liaquat College of Medicine and Dentistry together with Muhammad Sohail of the University of Karachi and collaborators at several Karachi institutions and Taif University in Saudi Arabia, analyzed 308 Gram-negative bacterial isolates recovered from urine samples of patients with catheter-associated urinary tract infections. The samples were collected between June and December 2024, and the work received ethical approval from the Institutional Review Board of Darul Sehat Hospital in Karachi, with written informed consent obtained from all participants or their legal representatives. The study was designed to answer three linked questions: how common carbapenem resistance is in this setting, which carbapenemase-encoding genes are responsible, and what patient characteristics are associated with carrying those genes.

Species identification revealed a familiar hierarchy of uropathogens. Escherichia coli was the dominant organism, accounting for 134 of the 308 isolates, or 43.5 percent, followed by Klebsiella pneumoniae with 96 isolates, or 31.2 percent. The remaining isolates included other Gram-negative species, among them Pseudomonas aeruginosa. This distribution mirrors global patterns of catheter-associated infection, in which Enterobacterales, the family of gut-dwelling bacteria that includes both E. coli and K. pneumoniae, colonize the urinary tract and catheter surfaces with ease. The ubiquity of these organisms in hospital plumbing, on catheter biofilms, and in patients’ own gut flora makes them persistent adversaries in intensive care units and general wards alike.

Antimicrobial susceptibility testing exposed a stark pattern of resistance to the older, cheaper, and more widely used drugs. Resistance to ceftriaxone, a third-generation cephalosporin, was found in 244 of 308 isolates, a rate of 79.2 percent, while resistance to ciprofloxacin, a fluoroquinolone, appeared in 238 isolates, or 77.3 percent. By contrast, resistance to the carbapenems remained lower but far from negligible: 104 isolates, or 33.8 percent, were resistant to meropenem, and 96 isolates, or 31.2 percent, were resistant to imipenem. That roughly one in three Gram-negative uropathogens from catheter-associated infections could shrug off carbapenems underscores how far these last-line drugs have been eroded in this clinical setting, leaving clinicians with progressively fewer options for seriously ill patients.

The molecular core of the study focused on five carbapenemase-encoding genes detected by polymerase chain reaction: bla_NDM, bla_OXA-48, bla_KPC, bla_IMP, and bla_VIM. These genes encode enzymes that hydrolyze carbapenems and most other beta-lactam antibiotics, rendering them ineffective. Among the 104 carbapenem-resistant isolates, bla_NDM, which encodes the New Delhi metallo-beta-lactamase, was by far the most prevalent, detected in 66 isolates, or 63.5 percent. bla_OXA-48, encoding the oxacillinase-48 beta-lactamase, came second at 40 isolates, or 38.5 percent. Notably, bla_KPC, bla_IMP, and bla_VIM were not reported as significant contributors in this collection, marking NDM and OXA-48 as the dominant resistance determinants in these Karachi hospitals.

The distribution of genes across species was not uniform, and this species-specific pattern carries practical implications for diagnostics and treatment. bla_NDM was particularly concentrated in K. pneumoniae, appearing in 31 of 48 carbapenem-resistant K. pneumoniae isolates, or 64.6 percent. bla_OXA-48, by contrast, was more predominant in carbapenem-resistant P. aeruginosa, detected in 4 of 10 such isolates, or 40 percent. The study also documented co-carriage of both bla_NDM and bla_OXA-48 in 12 of the 104 carbapenem-resistant isolates, or 11.5 percent. Dual carriage is especially concerning because enzymes from these two classes, a metallo-beta-lactamase and a class D carbapenemase, together dismantle a broader spectrum of beta-lactam drugs and can complicate the interpretation of phenotypic susceptibility tests, which may fail to flag resistance when multiple mechanisms interact.

Beyond cataloguing genes, the investigators used chi-square tests and binary logistic regression to identify independent predictors of carbapenemase gene carriage, with a p-value of 0.05 or less considered statistically significant. Three clinical factors emerged as independent predictors of gene positivity: admission to the intensive care unit, previous exposure to antibiotics, and catheterization lasting longer than seven days. Each of these factors fits a coherent biological and epidemiological narrative. ICU patients are exposed to the highest densities of resistant organisms and the most intensive antimicrobial use. Prior antibiotic exposure selectively eliminates susceptible strains, clearing the way for resistant ones to colonize. And prolonged catheterization gives bacteria time to form biofilms on the device surface, where they are shielded from both immune defenses and antibiotics and can freely exchange resistance genes on plasmids and other mobile elements.

The public health significance of these findings extends well beyond a single city. Carbapenemase genes, particularly bla_NDM, are notorious for their mobility, hitchhiking on plasmids that move readily between bacterial species and genera. A patient colonized with an NDM-producing E. coli strain can serve as a silent reservoir, disseminating the gene into hospital environments, water systems, and community settings. Because catheter-associated infections are so common, the urinary tract represents one of the largest and most underappreciated reservoirs for these genes in healthcare facilities. The identification of modifiable risk factors, especially catheter duration, provides concrete targets for intervention: strict catheter stewardship, daily assessment of the ongoing need for a catheter, and early removal are inexpensive measures that directly shorten the window in which resistance can emerge and spread.

The study also highlights the importance of molecular surveillance in an era where phenotypic testing alone may not capture the full resistance picture. Rapid PCR-based detection of bla_NDM and bla_OXA-48 in carbapenem-resistant isolates allows infection control teams to isolate carriers promptly, adjust antibiotic therapy, and interrupt transmission chains before outbreaks take hold. The authors note that the co-existence of multiple carbapenemase genes in a meaningful fraction of isolates further argues for comprehensive molecular panels rather than single-gene assays, since treatment decisions and infection control responses may differ depending on which enzymes are present. For laboratories in resource-limited settings, the study’s straightforward PCR approach offers a practical template for building such surveillance capacity.

Published open access in BMC Infectious Diseases with a permanent DOI, the study arrives as the global health community intensifies efforts against antimicrobial resistance, a threat the WHO has identified as one of the top challenges facing public health. The Karachi data, showing E. coli as the predominant uropathogen, bla_NDM as the leading carbapenemase in resistant Enterobacterales, and bla_OXA-48 as the more prevalent mechanism in resistant P. aeruginosa, add a valuable regional data point to the global map of resistance. More importantly, the clear linkage of gene carriage to ICU admission, prior antibiotic exposure, and extended catheterization converts an abstract molecular threat into a set of actionable clinical priorities. If hospitals act on these predictors, limiting unnecessary catheter days and curbing indiscriminate antibiotic use, the study suggests that the spread of carbapenemase genes in catheter-associated infections can be slowed, preserving the effectiveness of last-line antibiotics for the patients who need them most.

Subject of Research: Carbapenemase gene prevalence and risk factors in Gram-negative uropathogens causing catheter-associated urinary tract infections

Article Title: Molecular detection and risk factors of carbapenemase -encoding gene among the Gram-negative uropathogens associated with catheter-associated urinary tract infection

Article References: Kashif, S., Sohail, M., Uddin, F., Ansari, A., Alorabi, M., Khan, R. N., & Husain, S. (2026). Molecular detection and risk factors of carbapenemase -encoding gene among the Gram-negative uropathogens associated with catheter-associated urinary tract infection. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14568-w

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14568-w

Keywords: carbapenemase, bla_NDM, bla_OXA-48, catheter-associated urinary tract infection, antimicrobial resistance, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, carbapenem-resistant Enterobacterales, risk factors, PCR detection, hospital infection control