Epidemiology of Systemic and Ocular Toxoplasmosis and their Associations with Polymorphisms in Human Interferon Gamma and Tumour Necrosis Factor Cytokine Genes

Abstract

The aim was to determine the associations between interferon gamma/tumour necrosis factor gene polymorphisms and Toxoplama infection in a community-based epidemiological survey. Sera were tested for IgG and IgM antibodies using ELISA test kits. Ophthalmic examination included visual acuity, slit lamp biomicroscopy and dilated funduscopy. A serologic criterion was a positive test result for either IgG or IgM antibodies or both. Ocular toxoplamosis was diagnosed based on characteristics retinal lesions. Individuals with ocular infection served as cases and seropositive individuals without ocular disease as controls. There were 390 participants (mean age = 47.0 years), 30.3% males and 69.7% females. Seroprevalence of IgG and/or IgM antibodies was 85%. The study found a statistically significant relationship between Toxoplasma seropositivity and the following factors: contact with soil, presence of cats, older age, sources of drinking water, low levels of education, socioeconomic status, rural dwelling, and occupation (farmers and fishers/fish mongers). Ten (3%) subjects had toxoplasmic ocular lesions, contributing to 5.8% of visual impairment. Blindness occurred in 50% episodes of eye infections. The risk for developing Toxoplasma ocular lesions was old age (p = 0.028). Low prevalence of ocular infection was found in a population of high seropositivity. The results suggested contamination by sporulated oocysts as the major source of transmission. IFN-y +874T allele seemed to increase the risk of developing ocular lesions. Also, the presence of the less common TN F—308 A allelic form was found protective against the development of ocular infection in the present study.