Toxoplasma gondii is an extremely common parasite of animals and humans and an important opportunistic pathogen in immunocompromised patients. Our previous studies indicate that strains of T. gondii from North America and Europe comprise just three highly clonal lineages. More recent studies indicate a very different population structure in South America, consisting of distinct lineages with greater genetic diversity. Increasingly, toxoplasmosis has been recognized as a cause of ocular infection in otherwise healthy individuals from South America, where most common parasite lineages are highly virulent in animal models. However, knowledge about the population structure of T. gondii from much of the world remains unavailable. Our studies indicate that lineages from North America an Europe are related by a recent common ancestry and the inheritance of a monomorphic version of chromosome 1a (Chr1a*). Surprisingly, Chr1a* also recently been spreading into the South, where it may be associated with expansion of a few successful lineages. We will explore the hypothesis that Chr1a* carries particular genes that impart increased fitness, hence leading to clonal expansion of lineages inheriting this chromosome. The spread of clonalilty in T. gondii may also have influenced transmission and pathogenicity, and hence understanding the population structure is of direct importance to human disease. The proposed studies will enlist an international consortium of investigators to define the population structure of T. gondii. We will examine the genetic diversity of T. gondii, map the spread of Chr1a*, and test models for the origin and expansion of clonal lineages. Expected outcomes include: 1) characterize the genetic composition of T. gondii strains using traditional and microarray-based sequencing technologies 2) define the major haplotypes that comprise the global population structure, 3) characterize prototypic isolates for each haplotype, and 4) test isolates in animal models for the traits of transmission and virulence. Classical and molecular genetic methods will also be employed to identify genes that have driven the recent and highly successful expansion of T. gondii isolates in animals and humans around the world.

Public Health Relevance

Toxoplasma gondii has an highly unusual population structure and distinct lineages may be responsible for different clinical presentation in humans. The proposed studies will evaluate the global population structure of this parasite and define the biological traits, including transmission and virulence, of the major genotypes. The long term goal of these studies is to elucidate the molecular basis of the recent emergence of a few dominant lineages that cause the majority of human infections, which may facilitate development of improved detection methods and possible interventions against toxoplasmosis.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Special Emphasis Panel (ZRG1-IDM-B (02))
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Joy, Deirdre A
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Washington University
Schools of Medicine
Saint Louis
United States
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Lorenzi, Hernan; Khan, Asis; Behnke, Michael S et al. (2016) Local admixture of amplified and diversified secreted pathogenesis determinants shapes mosaic Toxoplasma gondii genomes. Nat Commun 7:10147
Shaik, Jahangheer S; Khan, Asis; Beverley, Stephen M et al. (2015) REDHORSE-REcombination and Double crossover detection in Haploid Organisms using next-geneRation SEquencing data. BMC Genomics 16:133
Wang, Zi T; Harmon, Steve; O'Malley, Karen L et al. (2015) Reassessment of the role of aromatic amino acid hydroxylases and the effect of infection by Toxoplasma gondii on host dopamine. Infect Immun 83:1039-47
Behnke, Michael S; Khan, Asis; Sibley, L David (2015) Genetic mapping reveals that sinefungin resistance in Toxoplasma gondii is controlled by a putative amino acid transporter locus that can be used as a negative selectable marker. Eukaryot Cell 14:140-8
Dubey, J P; Van Why, K; Verma, S K et al. (2014) Genotyping Toxoplasma gondii from wildlife in Pennsylvania and identification of natural recombinants virulent to mice. Vet Parasitol 200:74-84
Khan, Asis; Ajzenberg, Daniel; Mercier, Aurélien et al. (2014) Geographic separation of domestic and wild strains of Toxoplasma gondii in French Guiana correlates with a monomorphic version of chromosome1a. PLoS Negl Trop Dis 8:e3182
Behnke, Michael S; Zhang, Tiange P; Dubey, Jitender P et al. (2014) Toxoplasma gondii merozoite gene expression analysis with comparison to the life cycle discloses a unique expression state during enteric development. BMC Genomics 15:350
Khan, Asis; Shaik, Jahangheer S; Behnke, Michael et al. (2014) NextGen sequencing reveals short double crossovers contribute disproportionately to genetic diversity in Toxoplasma gondii. BMC Genomics 15:1168
Su, Chunlei; Khan, Asis; Zhou, Peng et al. (2012) Globally diverse Toxoplasma gondii isolates comprise six major clades originating from a small number of distinct ancestral lineages. Proc Natl Acad Sci U S A 109:5844-9
Mashayekhi, Mona; Sandau, Michelle M; Dunay, Ildiko R et al. (2011) CD8α(+) dendritic cells are the critical source of interleukin-12 that controls acute infection by Toxoplasma gondii tachyzoites. Immunity 35:249-59

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