Neuroinflammation is implicated in the pathophysiology of depression. Toxoplasma gondii (T. gondii) causes chronic brain inflammatory process and may thus contribute to both depression and its most serious complication, suicidal behavior. In this study, we hypothesized that latent toxoplasmosis may underlie current depression and/or suicidal behavior.
Currently depressed individuals (N = 384) and age, sex, and residence-matched healthy controls (HC) (N = 400) were tested for latent toxoplasmosis (i.e., positive serum T. gondii IgG antibodies). Exclusions included positive IgM and negative IgG antibodies indicating acute T. gondii infection and history of cognitive problems. Depression severity and history of lifetime suicide attempts were assessed using Beck Depression Inventory (BDI) and Columbia Suicide Severity Rating Scale, respectively.
Participants with seropositive anti-T. gondii IgG antibody had a significantly higher odds of being depressed compared with seronegative participants (OR = 2.9, 95% CI: 1.9–4.3; p < 0.001). BDI score was significantly different between depressed seropositive and depressed seronegative individuals (IgG＋: mean (SD)= 39.65 (11.83) vs. IgG−: mean (SD)= 33.44(9.80); t = 5.03, p < 0.001). Further, seropositive depressed participants were more likely to have prior history of actual suicide attempts compared with seronegative participants (OR= 6.2, 95% CI: 3.4–11.2, p < 0.001).
Latent toxoplasmosis may represent be a risk factor for depression and suicidal behavior. Screening for, and treatment of, underlying T. gondii infection may help improve depression and curb the increasing suicide rates. Future studies should prospectively test these hypotheses to be adequately implemented.