Life History Perspectives on Parasite Genotypes, Disease Outbreaks, and Wildlife Hosts for Toxoplasma gondii and Sarcocystis neurona

Abstract

The objectives of this study were to generate and analyze molecular genotyping data for the parasites, Sarcocystis neurona and Toxoplasma gondii, in an effort to: 1. Define the spectrum of parasite genotypes infecting wildlife hosts, 2. Identify evidence for genetic exchange (recombination) among parasite isolates, 3. Identify parasite genotypes responsible for disease outbreaks, and 4. Describe a causal link between parasite life history events and outbreak occurrence. Methods applied include evidence synthesis of previously published parasite molecular genotyping data and development and application of new parasite typing schemes to parasite genetic material recovered from outbreak events. Polymerase chain reaction and DNA sequencing based typing schemes were successfully developed for Sarcocystis neurona and Toxoplasma gondii. Findings revealed a diverse parasite gene pool circulating among wildlife hosts with evidence of genetic recombination among strains. Genetic typing of strains associated with disease outbreaks of both T. gondii and S. neurona revealed clonal outbreaks linked to water contamination by definitive host fecal shedding following the parasite sexual life cycle stage. Furthermore, the T. gondii outbreak clone was apparently a recently emerged recombinant strain. This suggests that the parasite sexual stage potentiates disease outbreaks by serving the dual roles of emerging new lines through recombination and rapidly amplifying and transmitting virulent strains through self-mating and fecal shedding. These findings indicate the definitive host stage is an essential target for disease prevention strategies.