Toxoplasma gondii is one of the most successful parasites on Earth. Its definitive hosts are members of the cat family, in whose intestines the organism undergoes sexual reproduction and sheds hardy oocysts into the environment through feces. These oocysts can survive in soil and water for months, resisting heat and desiccation, and are readily taken up by warm-blooded intermediate hosts, including humans. Infection in people typically occurs through three principal routes: ingestion of oocysts contaminating food, water, or soil; consumption of undercooked meat containing tissue cysts; and, critically for pregnancy, transplacental transmission from an acutely infected mother to her unborn child. In healthy adults, the infection is usually asymptomatic or produces a mild, flu-like illness that passes unnoticed. The immune system walls the parasite off in dormant tissue cysts, where it can persist for life. But in pregnancy, and in immunocompromised individuals, the stakes change dramatically.

When a woman acquires a primary T. gondii infection during gestation, the parasite can cross the placenta and invade fetal tissues, causing congenital toxoplasmosis. The consequences range from miscarriage and stillbirth to severe neurological damage, hydrocephalus, chorioretinitis leading to vision loss, and calcifications in the brain. The risk of transmission and the severity of disease depend heavily on the timing of infection: early in pregnancy, transmission is less likely but fetal damage, when it occurs, tends to be catastrophic, while later infection transmits more readily but often produces milder, sometimes delayed manifestations such as hearing loss or retinal disease diagnosed years after birth. This is precisely why serological surveillance of pregnant women matters. Knowing how many women have already been exposed, and therefore which mothers remain susceptible to a primary infection, allows health systems to target education and, where appropriate, diagnostic follow-up.

The research team, led by Verner Ndudiri Orish of the University of Health and Allied Sciences in Ho and including investigators from the University of Ghana, Ho Teaching Hospital, the Ghana Atomic Energy Commission, and collaborating institutions, enrolled 201 pregnant women aged 15 to 49 years who were attending their first antenatal care visit between 24 February and 7 April 2025. Consecutive sampling was used to minimize selection bias, and each participant completed a validated questionnaire covering sociodemographic characteristics, obstetric history, dietary practices, and environmental exposures, including contact with cats. Blood samples were collected in EDTA tubes and screened for T. gondii-specific immunoglobulin G and immunoglobulin M antibodies using a rapid diagnostic test. Statistical analysis was performed with IBM SPSS Statistics version 27, with logistic regression models used to identify independent predictors of seropositivity at a 95 percent confidence interval and a significance threshold of p less than 0.05.

The headline result was stark: 85 of the 201 women, or 42.5 percent, tested positive for T. gondii antibodies. The overwhelming majority of these infections, 96.5 percent, were IgG-only, indicating past exposure and the presence of dormant tissue cysts rather than active disease. Just 3.5 percent of seropositive women carried both IgG and IgM, a pattern that can suggest a recent or reactivated infection and would warrant closer clinical attention. An IgG-dominant profile means that most of the exposed women have already mounted an immune response that substantially reduces the risk of transmitting the parasite to a future fetus. However, the sheer proportion of women exposed before or during early reproductive life also means that a large fraction of the remaining population, more than half of the study cohort, remains susceptible to a primary infection, which is the scenario most dangerous for the developing fetus.

The regression analysis yielded two striking risk factors. The first was parity, the number of times a woman has previously given birth. Compared with nulliparous women, those pregnant with their first child, the primiparous group, had nearly four times the odds of seropositivity, with an adjusted odds ratio of 3.93 and a 95 percent confidence interval of 1.42 to 10.91. Multiparous women showed a similarly elevated odds ratio of 3.85, with a confidence interval of 1.50 to 9.87. This association is intriguing because it runs counter to a simple cumulative-exposure model, in which more years of life would be expected to translate into more opportunities for infection. The authors’ finding suggests that in this setting, parity may serve as a proxy for other exposures, such as household food-handling practices, rural environmental contact, or caregiving patterns that bring women into contact with contaminated soil or animals. Whatever the underlying mechanism, the signal was robust enough to survive adjustment for other variables in the model.

The second and perhaps most actionable risk factor was the handling of cat litter. Women who reported cleaning cat litter had more than seven times the odds of being seropositive compared with those who did not, with an adjusted odds ratio of 7.43 and a confidence interval of 2.06 to 26.76. This result aligns precisely with the parasite’s biology. Cats shed T. gondii oocysts in their feces, particularly after a recent primary infection, and these oocysts require one to five days in the environment to sporulate and become infectious. Litter boxes that are not cleaned daily therefore accumulate sporulated, infective oocysts, and the act of scooping them generates aerosols and dust that can be inhaled or transferred to the hands and mouth. The strong statistical association observed in Ho provides direct epidemiological confirmation of a transmission route that public health authorities in high-income countries have long emphasized in pregnancy advice: pregnant women should avoid changing cat litter altogether, or if they must, wear gloves and wash their hands thoroughly afterward.

The Ho findings sit within a broader African and Ghanaian context of remarkably high toxoplasmosis burden. Regional studies across Ghana have previously reported elevated seroprevalence among pregnant women, but data from the Volta Region specifically have been sparse, leaving a gap in the national picture. The new study fills that gap with a figure that exceeds many reported estimates from other parts of the world, where seroprevalence in pregnant women can range from under 10 percent in some northern European countries with strict food-safety and hygiene norms to over 50 percent in parts of Latin America and sub-Saharan Africa. High seroprevalence in a tropical setting is shaped by a convergence of factors: warm, humid climates that favor oocyst survival in soil; free-roaming cat populations; dietary practices that may include undercooked or improperly washed foods; limited access to clean water; and the absence of routine screening programs that would otherwise identify and counsel susceptible women.

The study’s implications for antenatal care policy in Ghana are considerable. Currently, toxoplasmosis is not part of routine antenatal screening in most Ghanaian facilities, where programmatic attention has understandably focused on HIV, malaria, syphilis, and anemia. Yet the biology of congenital toxoplasmosis makes a compelling case for at least targeted screening. Women who test IgG-negative at their first visit are the ones at genuine risk of a primary infection during pregnancy, and they are the ones who would benefit most from intensive hygiene counseling: avoiding cat litter, washing fruits and vegetables meticulously, cooking meat thoroughly, wearing gloves when gardening, and washing hands after contact with soil or raw meat. For women with IgG and IgM co-positivity, confirmatory testing, ideally with reference laboratory methods such as enzyme-linked immunosorbent assay and avidity testing, could distinguish recent from distant infection and guide decisions about treatment with spiramycin or pyrimethamine-based regimens, which can reduce the risk and severity of fetal transmission when initiated promptly.

The authors emphasize that their findings underscore the need for routine health education, improved hygienic practices, and serious consideration of toxoplasmosis screening within antenatal care programs to reduce maternal-fetal complications. The study received no external funding and was supported entirely by the investigators, and it was conducted with ethical clearance from the University of Health and Allied Sciences Research Ethics Committee under the principles of the Declaration of Helsinki, with written and verbal informed consent obtained from all participants. As a single-center cross-sectional study relying on rapid diagnostic tests rather than confirmatory serology, it has inherent limitations, including the potential for false-positive or false-negative results and the inability to establish causality between the identified risk factors and infection. Nevertheless, the message it delivers is difficult to ignore. In Ho Municipality, more than four in ten expectant mothers carry a parasite that most have never heard of, and the simple act of cleaning a cat’s litter box multiplies the odds of exposure sevenfold. Closing that knowledge gap, through education, hygiene interventions, and a renewed conversation about what belongs in the antenatal care package, could spare countless families the devastating and largely preventable consequences of congenital toxoplasmosis.

Subject of Research: Seroprevalence and risk factors of Toxoplasma gondii infection among pregnant women in the Volta Region of Ghana

Article Title: Seroprevalence of Toxoplasma gondii among pregnant women seeking antenatal care in Ho Municipality of the Volta Region of Ghana

Article References: Orish, V. N., Matthew, D., Ablordey, K., Squire, D. S., Arko-Mensah, J., De-graft Tawiah, J., Tsadidey, E., Adzah, D., Yeboah, E. A., Tetteh, R. E., Vikpebah, D. R., Nwaefuna, E. K., Lopez, D. M., Dah, A. K., Amoh, M., & Abaka-Yawson, A. (2026). Seroprevalence of Toxoplasma gondii among pregnant women seeking antenatal care in Ho Municipality of the Volta Region of Ghana. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14593-9

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14593-9

Keywords: Toxoplasma gondii, toxoplasmosis, pregnant women, seroprevalence, Ghana, antenatal care, congenital infection, cat litter, parasitology, public health, Volta Region, rapid diagnostic test

Extracellular vesicles are membrane-bound particles released by virtually all known cells, from bacteria to human neurons. They range from small exosomes, roughly 30 to 150 nanometers in diameter and born inside multivesicular bodies, to larger microvesicles that bud directly from the plasma membrane. Far from being cellular debris, these particles act as couriers: they carry proteins, lipids, and nucleic acids between cells, and their cargo can reprogram the recipient’s behavior. In the context of T. gondii, the review frames EVs as an extension of the parasite’s secretory arsenal, a parallel channel of communication that operates alongside, and sometimes in concert with, the classical apical secretion systems that parasitologists have studied for decades.

The technical foundations of this field rest on a growing toolkit for isolating and characterizing vesicles. The review catalogs the methods that have defined the state of the art: ultracentrifugation and size-exclusion chromatography for separation, nanoparticle tracking analysis and dynamic light scattering for sizing vesicle populations, transmission and scanning electron microscopy for direct visualization, and Western blotting, mass spectrometry, and immunocytochemistry for identifying the proteins that vesicles carry. Lipid composition is probed with techniques such as Fourier transform infrared spectroscopy, revealing envelopes enriched in phosphatidylcholine, phosphatidylethanolamine, sphingomyelins, ceramides, and triacylglycerols. Each method carries its own biases and limitations, and the authors emphasize that careful, standardized characterization is essential if the field is to distinguish genuine biological signaling from artifacts of preparation.

Biogenesis is where the story becomes mechanistically rich. Parasite-derived vesicles appear to draw on conserved eukaryotic machinery, including the endosomal sorting complexes required for transport, the ESCRT apparatus, and SNARE-mediated membrane fusion, pathways that T. gondii shares with its hosts despite being separated by more than a billion years of evolution. Multivesicular bodies within the parasite can package cargo into intraluminal vesicles that are released when these compartments fuse with the parasite’s surface. The result is a population of vesicles whose membrane composition and internal cargo reflect the physiology of the cell that made them, whether that cell is the parasite itself or the host cell it has commandeered. This dual origin is one of the review’s central conceptual points: the vesicles circulating in the blood or tissues of an infected animal are a mixture, some born of the parasite and some of the infected host, and both populations carry messages.

The cargo of T. gondii-associated vesicles reads like an inventory of the parasite’s most important virulence tools. Proteomic analyses have detected proteins associated with invasion and intracellular survival, including members of the rhoptry protein, rhoptry neck protein, microneme protein, dense granule protein, and surface antigen families, the very molecules the parasite uses to attach to, penetrate, and remodel host cells. Alongside these proteins travel regulatory microRNAs, small RNA molecules capable of silencing host genes, and bioactive lipids that can themselves trigger signaling cascades. The packaging of such a diverse molecular repertoire into a single nanoscale delivery vehicle positions EVs, in the authors’ framing, as multilayered effectors, capable of acting simultaneously on protein receptors, gene expression, and membrane biochemistry in the cells they encounter.

Functionally, the review organizes the evidence around three themes: infection priming, immune modulation, and neural reprogramming. Infection priming refers to the observation that vesicles released by the parasite or by infected cells can prepare host tissues for invasion, altering the local environment before the parasite itself arrives. Immune modulation is the better-documented phenomenon: vesicle cargo can shift the balance of inflammatory signaling, dampening the Th1-type responses that would otherwise clear the parasite and encouraging states of immune tolerance that permit long-term persistence. Because T. gondii establishes lifelong infection precisely by walking this immunological tightrope, vesicle-mediated modulation offers a compelling explanation for how the parasite sustains its delicate equilibrium with the host immune system over decades.

The neural dimension is perhaps the most provocative. T. gondii is unusual among parasites in its ability to form tissue cysts in the brain, and behavioral changes in infected rodents, including a curious loss of aversion to cat odor, have fascinated researchers for years. The review highlights evidence that vesicles can influence neural cells, carrying microRNAs and other regulatory molecules capable of reshaping gene expression in neurons and glia. The authors are careful to frame this as an emerging area: the mechanistic chain from vesicle uptake to altered neural circuitry remains incompletely mapped, and the field has not yet demonstrated a complete causal pathway from a specific vesicle cargo to a specific behavioral change. Even so, the possibility that a parasite can package gene-regulatory messages into vesicles that cross into neural tissue opens a research agenda with implications far beyond toxoplasmosis.

What elevates the review beyond a catalog of mechanisms is its translational argument. The same vesicles that mediate immune evasion could serve as diagnostic biomarkers: because their cargo reflects the presence and activity of the parasite, detecting parasite-associated vesicles or their molecular signatures in patient samples, through methods such as enzyme-linked immunosorbent assays, could offer a window into infection status that conventional serology cannot provide. As vaccine platforms, vesicles present a natural display of parasite antigens in a membrane context that mimics infection, potentially stimulating immunity without requiring live organisms. And as therapeutic delivery vehicles, they offer a biocompatible nanoscale capsule that could, in principle, be engineered to carry drugs or immunomodulatory molecules across biological barriers that defeat conventional formulations, including the blood-brain barrier that shields the parasite’s chronic cysts from most treatments.

The authors also confront the field’s growing pains honestly. EV research across all of biology suffers from reproducibility challenges: isolation methods yield heterogeneous populations, quantification is inconsistent between laboratories, and distinguishing parasite-derived vesicles from host-derived ones in infected samples is technically demanding. The review’s emphasis on standardized characterization, combining orthogonal techniques such as electron microscopy, nanoparticle tracking, and proteomic validation, reflects a maturing discipline recognizing that its boldest claims will only survive if its methods do. The mixture of vesicle origins in infected hosts means that attributing a biological effect to the parasite, rather than to the host’s own response, requires careful experimental design, often involving purified parasite cultures and comparison with vesicles from uninfected host cells.

Taken together, the review makes a persuasive case for a conceptual shift. Extracellular vesicles in T. gondii are not metabolic exhaust, not incidental shedding from a busy cell, but strategic molecular messengers that operate at the interface between parasite and host, shaping infection from its earliest moments to its lifelong persistence. The work, published open access under a Creative Commons license with support from Brazil’s CAPES system, synthesizes mechanistic biology with translational ambition, and it arrives at a moment when vesicle biology is exploding across medicine, from cancer to neurodegeneration. For a parasite that infects such a vast share of humanity, understanding how it whispers to its host, through packets far too small to see, may prove as important as understanding how it invades. The conversation between Toxoplasma and its host, it turns out, has been conducted partly in a language scientists are only now learning to read.

Subject of Research: Extracellular vesicle-mediated host–parasite communication in Toxoplasma gondii infection

Article Title: Extracellular vesicles in Toxoplasma gondii: molecular messengers at the host–parasite interface

Article References: Balbino, E. F., Buso, L. S., de Oliveira, M. M., de Souza Martins, M. A. F., Bovolin, M. F., de Freitas Barbosa, B., Oliveira Gomes, A., Ramirez, M. I., Costa, I. N., & Rossi, I. V. (2026). Extracellular vesicles in Toxoplasma gondii: molecular messengers at the host–parasite interface. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07622-8

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07622-8

Keywords: Toxoplasma gondii, extracellular vesicles, exosomes, host–parasite interaction, immunomodulation, microRNAs, vesicle biogenesis, proteomics, biomarkers, vaccine platforms, drug delivery, toxoplasmosis

Toxoplasma gondii is one of the most successful parasites on Earth, capable of infecting virtually all warm-blooded animals, yet most human infections go entirely unnoticed. In a healthy adult, the immune system usually contains the parasite, which then persists in a dormant tissue-cyst form, primarily in muscle and brain tissue. The danger arises when a woman acquires her first infection shortly before or during pregnancy. At that point, before protective antibodies have fully developed, the parasite can spread through the bloodstream, invade the placenta, and infect the fetus. Congenital toxoplasmosis can cause miscarriage, stillbirth, hydrocephalus, chorioretinitis that threatens vision, intracranial calcifications, seizures, and long-term neurodevelopmental impairment. Because primary infection in the mother is typically asymptomatic or produces only mild, flu-like symptoms, the only practical way to identify women at risk is through serological testing, which is precisely what has been missing in much of sub-Saharan Africa.

The research team, led by Yared Mulu Gelaw of Bahir Dar University together with collaborators including Jean-Pierre Gangneux and Florence Robert-Gangneux of Rennes, France, set out to fill that gap using a tool designed for exactly this kind of resource-limited setting. The Toxoplasma ICT IgG-IgM test manufactured by LD Bio is a lateral-flow immunochromatographic assay, the same technological family as the rapid tests familiar from malaria and HIV screening. A small blood sample, applied to the test cassette, migrates along a membrane carrying immobilized antigens; antibodies against Toxoplasma, if present, are captured and visualized as colored lines within minutes. No laboratory infrastructure, electricity, cold chain, or specialized technician is required. The trade-off is that the combined IgG-IgM format indicates whether a woman has ever been infected, but does not by itself distinguish a recent, potentially dangerous primary infection from long-standing, dormant immunity, a limitation the authors acknowledge explicitly.

Study participants were recruited using systematic random sampling among women presenting at less than 20 weeks of gestation, with the average participant enrolled at roughly 14 weeks of pregnancy. The cohort was predominantly urban, with 85.2 percent of women living in city areas, and had a mean age of 26.8 years. The median monthly household income was 5,000 Ethiopian Birr, a figure that situates most families well within the economic constraints that shape diet, hygiene, and access to care. Alongside the blood sample, each woman completed a structured questionnaire covering sociodemographic characteristics, obstetric history, and the dietary and hygienic practices long associated with Toxoplasma transmission, from handling raw meat to consuming unpasteurized dairy. Statistical analysis, performed with binary logistic regression at both bivariable and multivariable levels, then identified which factors independently predicted seropositivity.

The headline number, 75.8 percent seroprevalence, means that only about one in four pregnant women in the cohort lacked antibodies and therefore remained fully susceptible to a primary infection during pregnancy. Seroprevalence rose steadily with both age and parity, an expected pattern for a parasite acquired cumulatively over a lifetime of exposure: each additional year and each additional pregnancy increases the cumulative probability of having encountered Toxoplasma. Notably, the classic socioeconomic gradients often reported elsewhere did not appear here. Educational level, monthly income, occupation, urban versus rural residence, and self-reported hygienic behaviors showed no significant association with seropositivity, suggesting that in this setting the parasite is so widely distributed in the food and environment that wealth and education offer little protection.

What did matter were specific dietary exposures. After adjustment for other variables, women who reported eating undercooked meat had roughly 29 percent higher odds of being seropositive, while those who drank raw milk had 82 percent higher odds, the strongest single risk factor identified in the study. Each additional year of age raised the odds by about 9 percent, and each prior pregnancy by about 33 percent. These findings map cleanly onto the parasite’s known biology. Tissue cysts harboring slowly replicating bradyzoites survive in undercooked beef, lamb, and goat meat, and ingestion of these cysts is one of the two principal routes of human infection worldwide. Raw or unpasteurized milk, particularly from goats, has been implicated in outbreaks of toxoplasmosis and can carry the parasite when animals are actively infected. In a culinary culture where raw meat dishes are traditional and home consumption of unpasteurized dairy is common, these routes of transmission appear to dominate.

The absence of an association with cat ownership or contact deserves attention, because the domestic cat is the definitive host of Toxoplasma and the source of the environmentally resistant oocysts that contaminate soil, water, and vegetables. In this study, hygienic factors generally failed to predict seropositivity, which the authors interpret as evidence that foodborne transmission, rather than direct contact with cats or contaminated soil, is the dominant driver of infection in Bahir Dar. This has practical consequences for prevention. While advising pregnant women to avoid cleaning litter trays remains sensible wherever cats are kept, the far higher-yield interventions here are culinary: cooking meat thoroughly, washing hands and utensils after handling raw meat, and boiling or pasteurizing milk before drinking it.

The choice of screening technology is central to the study’s significance. Conventional serology, whether the Sabin-Feldman dye test, enzyme-linked immunosorbent assays, or chemiluminescence, requires equipped laboratories, trained staff, and reliable supply chains that many antenatal clinics in low-income countries cannot sustain. As a result, Toxoplasma screening during pregnancy is routine in France and several other European countries but essentially nonexistent across most of Africa, leaving the true burden of congenital infection unmeasured. A lateral-flow test that can be performed at the point of care during a first antenatal visit changes that calculus. The authors argue that the ease of use of the Toxoplasma ICT test makes serological screening of pregnant women feasible directly within antenatal care facilities, without referral to distant laboratories. A positive result identifies a woman who has been exposed; a negative result identifies the smaller but clinically crucial group of susceptible women who would benefit most from targeted prevention counseling.

The study does carry limitations that temper interpretation. Because the ICT format reports any Toxoplasma antibody without separately distinguishing IgG from IgM, the 75.8 percent figure represents lifetime exposure rather than the rate of active or recent infection, so it cannot directly estimate how many pregnancies in the cohort were actually threatened by congenital transmission. The cross-sectional design captures a single moment in pregnancy rather than following women forward to birth outcomes, and the reliance on self-reported dietary habits introduces the possibility of recall bias. Nevertheless, as the first application of rapid immunochromatographic screening for Toxoplasma in pregnant women in Ethiopia, the study establishes both a baseline burden estimate and a proof of concept for a screening strategy that could be replicated in other high-burden, low-resource settings.

The public health implications are considerable. With three-quarters of women already immune, universal primary prevention messaging would reach many who no longer need it, while the quarter who remain susceptible face a real and quantifiable risk from two modifiable habits: eating undercooked meat and drinking raw milk. The authors conclude that efforts should focus on raising women’s awareness of these risk factors, particularly the consumption of raw meat and raw milk, and that the operational simplicity of the ICT test opens the door to integrating Toxoplasma serology into routine antenatal care. For a parasite that has historically been invisible to the health systems most exposed to it, a fifteen-minute test at the first prenatal visit may be the beginning of making congenital toxoplasmosis a measurable, and ultimately preventable, problem in Ethiopia.

Subject of Research: Seroprevalence and risk factors of Toxoplasma gondii infection among pregnant women in Bahir Dar, Ethiopia, using rapid immunochromatographic testing

Article Title: First use of rapid ICT screening for Toxoplasma in pregnant women in Ethiopia: A multicenter study in Bahir Dar, Ethiopia

Article References: First use of rapid ICT screening for Toxoplasma in pregnant women in Ethiopia: A multicenter study in Bahir Dar, Ethiopia. (n.d.). https://doi.org/10.1371/journal.pntd.0014616

Image Credits: AI Generated

DOI: 10.1371/journal.pntd.0014616

Keywords: Toxoplasma gondii, toxoplasmosis, pregnancy, seroprevalence, immunochromatographic test, Ethiopia, Bahir Dar, congenital infection, antenatal care, foodborne transmission, raw milk, undercooked meat

The rationale for targeting dense granule antigens, or GRAs, rests on their central role in the parasite’s survival strategy. Once T. gondii invades a host cell, it seals itself inside a parasitophorous vacuole and secretes more than 70 GRA proteins that decorate the vacuole membrane, the intravacuolar network and even the host cell nucleus. These effectors allow the parasite to manipulate host cell function and evade destruction. The research team focused on six GRAs selected for their recent discovery and documented roles in virulence or immunogenicity: GRA15, a well-characterised immunogen that activates the NF-κB pathway; GRA60, a virulence factor acting alongside ROP18; GRA76, identified in 2024 as a growth factor; GRA83, which provokes innate immune responses; and two novel effectors, GRA-α and GRA-β, shown to suppress parasite replication and cyst formation.

No approved vaccine exists for human toxoplasmosis. The only licensed product, the live-attenuated Toxovax used in sheep, cannot be given to people because of its residual pathogenic potential. Existing drug therapies for the acute tachyzoite stage often carry side effects and do not eliminate the dormant tissue cysts that cause lifelong infection. This therapeutic gap has pushed researchers toward reverse vaccinology, the computational discipline that screens pathogen genomes for the most promising antigenic fragments before any experiment begins. By filtering candidates in silico first, laboratories can save years of work, reduce costs and avoid animal testing of constructs destined to fail.

The epitope-mapping stage was deliberately stringent. The team retrieved the amino acid sequences of the six GRAs from the ToxoDB database and predicted linear B-cell epitopes using three independent web servers, retaining only fragments identified by at least two tools. Each surviving epitope was then scored for antigenicity with VaxiJen, screened for allergenicity with AllergenFP and checked for water solubility. In parallel, the researchers predicted cytotoxic T-lymphocyte epitopes of nine or ten residues bound by MHC class I molecules, and helper T-lymphocyte epitopes of fifteen residues bound by MHC class II, selecting the strongest allele-epitope combinations by percentile rank. CTL candidates underwent additional testing for immunogenicity and interferon-gamma induction potential, while HTL candidates were screened for toxicity as well.

From this filtering emerged eighteen final epitopes: six B-cell, six CTL and six HTL segments drawn from the six GRAs. The team then assembled four vaccine constructs, each combining the same epitope payload with a different immunostimulatory adjuvant. RS09-Toxo carried the synthetic TLR-4 agonist peptide RS-09; RSFN-Toxo was double-adjuvanted with RS-09 and human interferon-gamma; 50S-Toxo used a Mycobacterium tuberculosis ribosomal protein; and Rpf-Toxo employed the M. tuberculosis resuscitation-promoting factor E, RpfE. Flexible glycine-serine linkers, proteasomal cleavage sites and the rigid EAAAK spacer held the domains apart, and a C-terminal histidine tag enabled purification. The adjuvant choices were not arbitrary: all favour the Th1-type immunity that is critical for clearing intracellular pathogens such as T. gondii.

Biochemical profiling separated the field quickly. All four constructs scored highly for antigenicity, with values ranging from 0.9148 for Rpf-Toxo to 2.1188 for RS09-Toxo, and none was predicted to be allergenic. However, the ProtParam analysis revealed a critical weakness in the two most antigenic designs: RS09-Toxo and RSFN-Toxo carried instability indices of 60.23 and 50.51, well above the threshold of 40 that marks a protein as unstable in laboratory conditions. Only 50S-Toxo, with an instability index of 24.83, and Rpf-Toxo, at 35.41, passed the stability test, and both showed respectable aliphatic indices suggesting moderate thermal tolerance. All four constructs were hydrophilic, as indicated by negative GRAVY scores, and all exceeded the solubility threshold of the Protein-Sol predictor.

With Rpf-Toxo selected as the lead candidate, the team turned to structural biology. Homology modelling with I-TASSER produced a three-dimensional model that was then refined with the GalaxyRefine server, yielding improved geometry: 86.1 percent of residues fell into favoured Ramachandran regions, the MolProbity score dropped to 2.145 and the clash score fell to 9.6. The researchers candidly note that this figure remains below the 90 percent expected of high-resolution crystal structures, a limitation they attribute to the flexible spacers inherent in multi-epitope constructs. Molecular docking against the human TLR-4 receptor, the innate immune sensor central to Th1-polarised responses against the parasite, produced a stable predicted complex with a binding energy of −20.6 kcal/mol, although the authors caution that the corresponding dissociation constant of 7.3 × 10⁻¹⁶ M likely reflects overestimation by the PRODIGY algorithm rather than a physically realistic affinity.

Immune simulation with the C-ImmSim server, modelling a three-dose schedule at days 1, 84 and 186, painted an encouraging picture. Combined IgG and IgM titres peaked above 170,000 at day 65, memory B-cells reached 500 cells per cubic millimetre and settled at a stable set-point of around 200, and the helper T-cell population included roughly 1,800 memory cells that persisted through day 350. Interferon-gamma levels climbed to approximately 380,000 ng/mL, a signature consistent with the Th1-skewed response needed to eliminate intracellular tachyzoites, and natural killer cell activity peaked near 380 cells per cubic millimetre. Six conformational B-cell epitopes were also predicted on the folded surface of the construct, with ElliPro scores between 0.515 and 0.859, suggesting multiple antibody-accessible sites.

Safety and manufacturability checks completed the computational dossier. A BLASTp search against the human proteome found no significant homology, reducing the risk of autoimmune cross-reactivity, and the sequence was reverse-translated and codon-optimised for expression in E. coli K12, raising the codon adaptation index toward 1.00 and adjusting GC content to 65.63 percent. Restriction sites for Eco53kI and EcoRV, a Shine-Dalgarno ribosome-binding sequence and a stop codon were added to enable directional cloning into the pET-28a(+) vector for recombinant production.

The authors are emphatic that every result remains theoretical until confirmed experimentally. They list a series of limitations, including algorithmic bias in epitope prediction, the simplified nature of immune simulations, the absence of molecular dynamics analysis of the vaccine-receptor complex, and the lack of conservation analysis across genetically diverse T. gondii strains, which will be essential for assessing broad cross-protection. They also flag the inherent risks of multi-epitope design, such as epitope competition or immune masking, which flexible linkers can mitigate but not guarantee against. The proposed next steps include molecular dynamics simulations of the TLR-4 complex, advanced delivery platforms such as liposomes and nanoparticles, and challenge studies in murine models. If those experiments succeed, Rpf-Toxo could represent a meaningful step toward a long-sought human vaccine against one of medicine’s most persistent parasites.

Subject of Research: Immunoinformatic design of a multi-epitope vaccine candidate against Toxoplasma gondii based on dense granule antigens

Article Title: Rpf‐Toxo: A Preliminary Computationally Designed Dense Granule Antigen‐Based Multi‐Epitope Vaccine Against Toxoplasma gondii

Article References: Safari, M. H., Hosseini, S. A., Ghiabi, S., Ghiabi, S., Siamian, D., Majidiani, H., Irannejad, H., & Asghari, A. (2026). Rpf‐Toxo: A Preliminary Computationally Designed Dense Granule Antigen‐Based Multi‐Epitope Vaccine Against Toxoplasma gondii. Veterinary Medicine and Science, 12(5), Article e71189. https://doi.org/10.1002/vms3.71189

Image Credits: AI Generated

DOI: 10.1002/vms3.71189

Keywords: Toxoplasma gondii, toxoplasmosis, multi-epitope vaccine, dense granule antigens, reverse vaccinology, immunoinformatics, TLR-4, RpfE adjuvant, molecular docking, immune simulation, epitope prediction, vaccine design