2026 ECNP Congress

PS03-3180

Neurocognitive and psychiatric outcomes of parasitic infections

Mauro Scala — B. Martin-Maldonado, L. Rico-San Román, P. Zeinoun, M.F. Arshad, A. Serretti, P. Morrondo, M. Colizzi, G. Fanelli, A. Scala · Universidad Europea de Madrid, Faculty of Biomedical and Health Sciences, Madrid, Spain

2026 ECNP Congress

Introduction

The multifactorial aetiology of psychiatric disorders remains only partially understood. In addition to genetic and psychosocial factors, initial evidence suggests that infectious agents, particularly neurotropic pathogens, may influence psychiatric and neurocognitive outcomes through mechanisms such as neuroinflammation, blood–brain barrier disruption, and immune–brain interactions. Among parasites, Toxoplasma gondii is the most extensively studied, with meta-analytic evidence showing that seropositive individuals have approximately two- to three-fold higher odds of schizophrenia, bipolar disorder (BD), and obsessive–compulsive disorder (OCD) compared with seronegative controls [1-2]. Other parasitic infections may also contribute to cognitive and behavioural alterations, but evidence remains limited and inconclusive.

Aims

This structured narrative review synthesised evidence on associations between non-T. gondii parasitic infections and psychiatric or neurocognitive outcomes, and explored potential underlying mechanisms.

Methods

A comprehensive literature search was conducted in PubMed, Web of Science, and CINAHL from inception to August 2025. Observational studies investigating associations between non-T. gondii parasitic infections and psychiatric or neurocognitive outcomes assessed using clinical, diagnostic, or validated measures were included. Two reviewers independently screened studies, extracted data, and resolved discrepancies with senior investigators.

Results

Twenty-seven observational studies (i.e., community-based surveys, clinical cohorts, and hospital-based case–control investigations), including over 15,000 participants from Africa, Asia, and the Americas, were identified. Helminthic infections accounted for the largest proportion of studies (k=17), particularly Taenia solium (k=7) and Toxocara spp. (k=5), followed by protozoan infections (k=9), mainly Trypanosoma cruzi (k=4) and Plasmodium spp.(k=3). Neurocognitive impairment, including deficits in executive function, memory, and attention, was most consistently reported in infections with documented or plausible central nervous system (CNS) involvement, such as T. solium (k=4), Toxocara spp (k=3), and T. cruzi (k=2). In contrast, depressive and anxiety symptoms were more frequently reported in primarily non-neurotropic infections such as lymphatic filariasis (k=3), malaria (k=2), and leishmaniasis (k=1). Across parasite taxa, associations were more consistently reported for symptom domains than for categorical psychiatric diagnoses, with substantial heterogeneity in study design, outcome definition, infection ascertainment, and adjustment for socioeconomic factors.

Conclusions

Although the available evidence is observational and heterogeneous, it is consistent with biologically and socially plausible links between non–T. gondii parasitic infections and psychiatric or neurocognitive outcomes. The latter appeared more consistently associated with infections involving the CNS, potentially reflecting direct neural invasion, chronic neuroinflammation, and microvascular injury. Psychiatric symptoms in systemic infections may instead reflect systemic inflammation, neuroimmune dysregulation, illness burden, stigma, and socioeconomic adversity. These findings support integrated care approaches addressing infectious and mental-health domains, particularly in endemic and resource-limited settings. No included studies originated from Europe, indicating a research gap in high-income settings rather than evidence of absence [3]. Longitudinal studies with standardized psychiatric and cognitive phenotyping, and rigorous control for socioeconomic and clinical confounders are required to clarify causal relationships and inform prevention and intervention strategies.

References

  1. Bartolomé Del Pino, L.E., Zanón-Moreno, V., 2024 Systematic Review on the Relationship between Toxoplasmosis and Mental Disorders. Actas Esp Psiquiatr 52(2):149–160.
  2. Abdoli, A., Olfatifar, M., Eslahi, A.V., Moghadamizad, Z., Samimi, R., Habibi, M.A., et al. 2024 A systematic review and meta-analysis of protozoan parasite infections among patients with mental health disorders: an overlooked phenomenon. Gut Pathog 16(1):7.
  3. Cobzaru, R.G., Ripa, C.V., Ursu, R.G., Ripa, M.R., Damian, C., Iancu, L.S., 2025 Toxocara Seroprevalence in Europe and Considerations for Future Research. Pathogens 14(11):1117.