Toxoplasma gondii is one of the most successful parasites on Earth. It reproduces sexually only in cats, but its infectious oocysts shed in cat feces can contaminate soil, water, and food, while tissue cysts harbored in undercooked meat provide another common route of infection. In healthy people, the parasite usually causes mild or unnoticed symptoms before settling into a lifelong dormant state, encysted within muscles and the brain. The immune system keeps it in check, but it never eliminates it entirely. That delicate equilibrium is what makes the parasite so dangerous for people whose defenses are compromised. In immunocompromised patients, dormant cysts can reactivate, and newly acquired infections can escalate into life-threatening encephalitis, pneumonia, or systemic disease.

Beta-thalassemia major sits at an unusual intersection of vulnerability. Patients cannot produce adequate functional hemoglobin because of genetic defects in the beta-globin chain, and without regular transfusions of donor red blood cells every few weeks, they would not survive childhood. Decades of transfusion therapy, however, bring their own consequences: iron overload that itself impairs immune function, splenectomy in many patients that removes a key immune filter for blood-borne pathogens, and chronic inflammatory states that dysregulate cellular immunity, the very arm of the immune system, driven by T cells, that normally keeps Toxoplasma dormant. Layered on top of this is the theoretical possibility that the parasite could be transmitted directly through transfused blood, since Toxoplasma tachyzoites, the rapidly dividing form, can circulate in donor blood, and the parasite has been shown to survive in stored blood products under laboratory conditions.

To quantify the association, the research team followed the PRISMA reporting guidelines and searched PubMed, Scopus, and Web of Science from database inception through July 24, 2025. From an initial pool of 45 records, fourteen studies met the inclusion criteria: eleven case-control studies and three cross-sectional studies that reported IgG or IgM seropositivity for Toxoplasma gondii in beta-thalassemia major patients. Two reviewers independently extracted the data, a standard safeguard against extraction errors. The investigators pooled prevalence estimates using random-effects models, which do not assume that all studies estimate the same underlying true value and therefore better accommodate clinical and methodological diversity across settings. Heterogeneity, the statistical signature of between-study variation, was assessed with the I² statistic and Cochran’s Q test, and the methodological quality of each study was appraised using the design-specific Joanna Briggs Institute checklists.

The headline numbers are striking. The pooled prevalence of Toxoplasma infection among thalassemia patients was 21.5 percent, with a 95 percent confidence interval of 16.2 to 27.9 percent. Breaking the results down by antibody class, the seroprevalence of IgG, which indicates past exposure and chronic, latent infection, reached 30.0 percent, while IgM, a marker of recent or active infection, stood at 4.8 percent. When the researchers compared patients directly with healthy controls, the overall pooled risk ratio was 2.30, meaning thalassemia patients had more than twice the odds of testing positive. The subgroup analysis sharpened the picture: the risk ratio for IgG seropositivity was 2.05, while for IgM it climbed to 3.46, suggesting that recent infection may be disproportionately elevated in this population, a pattern that would be consistent with ongoing exposure rather than merely accumulated lifetime risk.

Rigorous meta-analyses live or die by their robustness checks, and this one ran the full gauntlet. Eight of the fourteen studies were rated high quality, one moderate, and five low, and critically, the pooled prevalence was not inflated by the lower-quality studies, a common pitfall in observational syntheses. Leave-one-out sensitivity analysis, in which each study is removed in turn to test whether any single dataset drives the result, confirmed the stability of the pooled estimates. Meta-regression found no significant effect of publication year or sample size on the observed heterogeneity, although subgroup analysis did identify study design as a potential source of that variation, with the very high I² values of 94.0 percent overall reflecting substantial statistical diversity among the included populations, assays, and diagnostic methods.

The analysis was less reassuring on the question of publication bias. Funnel plot asymmetry was statistically significant, with Begg’s test yielding a p-value of 0.0007 and Egger’s test a p-value below 0.0001, patterns that often arise when small studies with dramatic findings are published more readily than small null studies. Trim-and-fill analysis, a statistical imputation technique that estimates how many studies might be missing from the funnel plot, suggested that unpublished studies could be absent from the risk-ratio outcomes, meaning the true association, while likely real, could be somewhat smaller than the headline estimate of 2.30.

The authors are careful, and rightly so, about what the data cannot show. Seroprevalence studies detect antibodies, not the parasite itself, and they cannot distinguish between infection acquired through contaminated food or water, reactivation of latent infection under immune pressure, and transmission via transfused blood. All three mechanisms are biologically plausible in thalassemia patients. Iron overload is known to impair macrophage and T-cell function, potentially allowing latent cysts to reactivate. Splenectomized patients clear intracellular pathogens less effectively. And transfusion transmission, while never proven in this analysis, remains a theoretical concern given that seronegative donors are not routinely screened for Toxoplasma in most blood banks, unlike for HIV, hepatitis B, hepatitis C, and syphilis. The observational design of every included study means causality cannot be assigned to any of these pathways.

Even with those caveats, the practical implications are difficult to ignore. Millions of people worldwide live with thalassemia, concentrated in the Mediterranean, Middle East, and South and Southeast Asia, regions that overlap substantially with areas of high Toxoplasma endemicity. The finding that roughly one in five thalassemia patients in the pooled studies showed serological evidence of infection, and that recent infection markers were more than three times as common as in controls, gives clinicians a concrete reason to consider toxoplasmosis in the differential diagnosis of febrile or neurologically symptomatic thalassemia patients. It also strengthens the case, as the authors argue, for evaluating preventive strategies, from donor screening studies to patient education about food hygiene, in this vulnerable population. Whether routine Toxoplasma screening of blood donations is justified will require direct evidence of transfusion-transmitted cases, cost-effectiveness modeling, and an assessment of how frequently the parasite survives standard blood storage, questions that this meta-analysis cannot answer but that its results now make considerably harder to defer.

What the study ultimately delivers is a well-characterized signal demanding mechanistic follow-up. The statistical work is thorough, the sensitivity analyses are reassuring, and the authors’ transparency about publication bias and the limits of observational evidence reflects the kind of epistemic discipline that meta-analyses of this kind require. For the thalassemia community, the message is not alarm but attention: a parasite that most people shrug off may deserve a place on the clinical radar of transfusion-dependent patients, and the blood supply that keeps them alive may deserve a closer look for one of the world’s most widespread and quietly persistent pathogens.

Subject of Research: Toxoplasma gondii seroprevalence and infection risk in patients with beta-thalassemia major

Article Title: Elevated seroprevalence and risk of Toxoplasma gondii infection in patients with beta-thalassemia major: a systematic review and meta-analysis

Article References: Lesani, S., Hayati, F., & Boozhmehrani, M. J. (2026). Elevated seroprevalence and risk of Toxoplasma gondii infection in patients with beta-thalassemia major: a systematic review and meta-analysis. BMC Infectious Diseases. https://doi.org/10.1186/s12879-026-14558-y

Image Credits: AI Generated

DOI: 10.1186/s12879-026-14558-y

Keywords: Toxoplasma gondii, beta-thalassemia major, seroprevalence, meta-analysis, blood transfusion, transfusion-transmitted infections, immunocompromised patients, IgG antibodies, IgM antibodies, publication bias, systematic review, preventive strategies