Abstract
Toxoplasma gondii is an obligate intracellular protozoan parasite distributed worldwide that infects a wide range of warm-blooded animals, including humans. Recent studies sought to clarify the relationship between the alleles GRA15, ROP5, ROP16, ROP17, and ROP18 and the virulence of T. gondii isolates in mice. This work aims to analyze the variability of genes that express T. gondii virulence proteins of 103 strains. Most strains were virulent for mice (76/103-73.79%); within these, 30 were 100% lethal, and 46 caused a cumulative mortality range from 20% to 93%. For the GRA15 marker, most strains presenting allele 2 were non-lethal. For the ROP17 marker, allele 4 was associated with mortality, compared to allele 1. For the ROP18 marker, alleles 1 and 4 were associated with mortality, compared to alleles 2 and 3. A combined analysis of alleles showed low cumulative mortality when the strains presented alleles 3 and 1 for ROP18 and ROP16, respectively. On the other hand, allele 4 of ROP17 was a determinant for virulence when associated with ROP18 allele 3 and ROP16 allele 1. Our analysis shows that ROP18 is the primary determinant of the virulence of atypical strains in mice. Additionally, ROP17 genotyping should not be overlooked, as it has proven critical to enhance this prediction.