Identification of Genotype–restricted Anti–Toxoplasma gondii Antibodies Among Individuals Infected in an Epidemic

Abstract

Abstract: : Purpose:To identify genotype–restricted antibodies present in the serum of individuals infected during a T. gondii epidemic that was characterized by a high prevalence of ocular toxoplasmosis. Methods:We used an assay described by Kong and associates (J Infect Dis 2003;187:1484–95), which utilizes a series of polymorphic peptides derived from highly immunogenic T. gondii–secreted proteins. The peptides were used to distinguish serologically between infections caused by T. gondii Type II versus Type I/III. Blood specimens were obtained from 40 residents of Santa Isabel do Ivai, Brazil, the site of a recent epidemic of toxoplasmosis. The presence or absence of infection was confirmed using a commercially available immunofluoresence assay. Specimens were tested against the panel of peptides to detect genotype–restricted antibodies present in the serum of infected individuals. A Type I parasite had previously been isolated from the water supply that is believed to have been the source of all infections, based on epidemiological studies. Results:Among 22 T. gondii–infected individuals, 15 (68%) had assay results consistent with a Type I/III infection. Among 18 individuals without documented T. gondii infection, 1 (5%) had assay results consistent with a Type I/III infection. We did not find evidence of Type II infections in any individuals. Conclusions:Assay results support the epidemiologic evidence for a Type I infection in this outbreak. The assay appears to be a promising tool for population–based studies of T. gondii infections, and may contribute to a better understanding of the pathogenesis and the spectrum of the clinical manifestations of ocular toxoplasmosis.

Keywords: toxoplasmosis • clinical laboratory testing • microbial pathogenesis: clinical studies