<i>Toxoplasma gondii</i> Serointensity and Seropositivity: Heritability and Household-Related Associations in the Old Order Amish

• Main Authors: Allyson R. Duffy, Jeffrey R. O’Connell, Mary Pavlovich, Kathleen A. Ryan, Christopher A. Lowry, Melanie Daue, Uttam K. Raheja, Lisa A. Brenner, André O. Markon, Cecile M. Punzalan, Aline Dagdag, Dolores E. Hill, Toni I. Pollin, Andreas Seyfang, Maureen W. Groer, Braxton D. Mitchell, Teodor T. Postolache
• Format: Article
• Language: English
• Published: MDPI AG 2019-10-01
• Series: International Journal of Environmental Research and Public Health
• Subjects: environment; household; genetics; heritability; infection; mental illness; parasitic infection; <i>toxoplasma gondii</i>
• Online Access: https://www.mdpi.com/1660-4601/16/19/3732

<i>Toxoplasma gondii</i> (<i>T. gondii</i>) is an intracellular parasite infecting one third of the world&#8217;s population. Latent <i>T. gondii</i> infection has been associated with mental illness, including schizophrenia and suicidal behavior. <i>T. gondii</i> IgG antibody titers were measured via ELISA. The heritability of <i>T. gondii</i> IgG was estimated using a mixed model that included fixed effects for age and sex and random kinship effect. Of 2017 Old Order Amish participants, 1098 had positive titers (54.4%). The heritability for <i>T. gondii</i> serointensity was estimated to be 0.22 (<i>p</i> = 1.7 &#215; 10^&#8722;8 and for seropositivity, it was estimated to be 0.28 (<i>p</i> = 1.9 &#215; 10^&#8722;5). Shared household environmental effects (i.e., household effects) were also determined. Household effects, modeled as a random variable, were assessed as the phenotypic covariance between any two individuals who had the same current address (i.e., contemporaneous household), and nuclear household (i.e., the phenotypic covariance between parents and children only, not other siblings or spouses). Household effects did not account for a significant proportion of variance in either <i>T. gondii</i> serointensity or <i>T. gondii</i> seropositivity. Our results suggest a significant familial aggregation of <i>T. gondii</i> serointensity and seropositivity with significant heritability. The shared household does not contribute significantly to family aggregation with <i>T. gondii</i>, suggesting that there are possible unmeasured non-household shared and non-shared environmental factors that may play a significant role. Furthermore, the small but significant heritability effects justify the exploration of genetic vulnerability to <i>T. gondii</i> exposure, infection, virulence, and neurotropism.