Authors

C M Hamilton¹; L Black¹; S Oliveira³; A Burrells¹; P M Bartley¹; F Chianini¹; E A Innes¹; P J Kelly²; F Katzer¹;  ¹ Moredun Research institute, UK;  ² Ross University School of Veterinary Medicine, United States;  ³ Universidade de São Paulo, Brazil

Discussion

Toxoplasma gondii is a ubiquitous protozoan parasite capable of infecting all warm-blooded animals, including humans. Disease outcome can vary depending on a number of factors, including genetic diversity of the infecting strain. The aim of this study was to investigate the pathogenicity of eight genotypically distinct isolates of T. gondii. Eight groups of 15 Swiss Webster mice were inoculated intraperitoneally with 200 T. gondii tachyzoites (one isolate per group) &hypen; six were atypical isolates previously isolated from free-roaming chickens in St. Kitts (Caribbean), one isolate was the Type II Moredun strain (M4) and one isolate was an atypical Brazilian strain (BrI). Mice were monitored for signs of toxoplasmosis and euthanized when they reached a defined end point or at 4 weeks post-infection. Percentage mortality was recorded for 10 mice per group, and 5 mice per group were euthanized at day 8 p.i. and tissues were collected for parasite quantification, histopathology and RNA extraction and quantification of cytokines. Three of the isolates were acutely virulent for mice (100% mortality), 3 isolates were moderately virulent (30-70% mortality) and 2 isolates were non-virulent (0-20% mortality). The acutely virulent and moderately virulent strains had Type I and Type III ROP5 alleles, respectively, which are associated with virulence. Mice infected with acutely virulent isolates had significantly higher levels of parasite DNA in their lungs at day 8 p.i., and also had more severe pathology.