Transmission pattern of major clonal lineages of <i>Toxoplasma gondii</i>

Toxoplasma gondii is the most successful zoonotic pathogen known today. One-third of people are chronically infected worldwide. Different strains of T. gondii shows variability in mouse virulence which may potentially correlate with disease manifestation in humans. As a result, mouse is used as the model organism to study the virulence of T. gondii strains. To study the virulence on a global scale, it is necessary to establish a standardized approach for mice virulence assays. Thus, we review the methodologies used in different labs and put forth standardized approaches to study the T. gondii virulence in mice (Chapter 1). Recent advances in diversity and population structure of T. gondii had shown that even though the dominant type II strain is spread globally, it is particularly dominant in the region of Europe. Thus, to understand the origin and transmission pattern of the type II dominant lineage of T. gondii (Chapter 2), we tested the hypothesis that the current distribution structure and dominance of type II T. gondii in Europe is because the most recent common ancestor (MRCA) of type II originates in the continent of Europe. Based on our study we found that type II dominant lineage originated in the Old World and has transmitted to the New World (America). To further examine the migration pattern of second most dominant type III T. gondii, diversity among isolates was analyzed. Based on previous knowledge, in Chapter 3 we tested the hypothesis that, despite the diversity of genotypes in South America, the higher frequency of type III lineage is because the most recent common ancestor (MRCA) of type III originated on this continent. Our study revealed that origin of type III lineage is in the New World close to Central America and that the dissemination pattern is from New World to the Old World. In Chapter 4 we studied the seroprevalence rates for 471 and genotyped (n=19) wild life samples of T. gondii in the southeastern United States. We found high seroprevalence rates amongst game meat animals (white-tailed deer and feral hogs) which could be a potential risk for humans consuming contaminated meat.