Toxoplasma gondii is a common parasitic infection of humans where it normally causes uncomplicated yet persistent infections. Reactivation of chronic infection can lead to severe disease in immunocompromised patients, including those with HIV-AIDS. With the advent of HAART therapy, the frequency of toxoplasmosis has decreased. However, there are still many areas of the world, and susceptible patient populations, were advanced HAART therapy is not widely or effectively implemented. Hence, toxoplasmosis presents a continued risk to immunocompromised patients due to the high prevalence of chronic infection and limitations of existing antibiotics, which do not eradicate chronic infections. Our studies are designed to define the molecular basis of pathogenesis in T. gondii, focusing on more virulent parasite lineages that may pose greater risk in immunocompromised patients. We have previously used genetic analyses of the clonal lineages of North America to identify virulence genes in T. gondii. However, T. gondii strains are much more diverse and undergo greater genetic exchange in other regions of the world. For example, the majority of South American strains are acutely virulent in the mouse model and such strains are frequently found in HIV positive patients where they cause severe CNS disease. The basis for this enhanced pathogenicity is presently unknown, but importantly, it cannot be explained by known virulence determinants. In preliminary studies, we have developed several new genetic crosses between highly virulent South American strains and less virulent lineages typical of North America. The proposed studies will use genetic mapping to identify virulence determinants of T. gondii and test the role of these parasite effectors in mediating survival in human cells. In preliminary studies, we have shown that IFN-?-activated human cells restrict the growth of T. gondii in a strain-specific manner. The proposed studies will define the cellular and molecular basis of this resistance pathway in human cells. Genetic approaches will be used to identify the molecular determinants of parasite virulence. The overall goal of our studies is to define the molecular mechanisms by which T. gondii overcomes host resistance, thus enhancing its survival and leading to more severe disease. Successful identification of parasite virulence factors may lead to improved detection and/or improved interventions designed to combat infection.

Public Health Relevance

Toxoplasma gondii is a widespread parasite that can cause severe disease in immunocompromised patients, especially those with HIV-AIDS. Our studies seek to define parasite factors that contribute to the severity of disease, especially in strains tat are more commonly associated with reactivation in HIV-AIDS patients. By understanding the virulence determinants of the parasite, it may be possible to develop new therapeutic approaches to combat or prevent human infection. The findings are highly relevant to the pathology of latent and reactivated toxoplasmosis in individuals with HIV-AIDS.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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AIDS-associated Opportunistic Infections and Cancer Study Section (AOIC)
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Joy, Deirdre A
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Washington University
Schools of Medicine
Saint Louis
United States
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Cabral, Gabriel R de Abreu; Wang, Zi T; Sibley, L D et al. (2018) Inhibition of Nitric Oxide Production in Activated Macrophages Caused by Toxoplasma gondii Infection Occurs by Distinct Mechanisms in Different Mouse Macrophage Cell Lines. Front Microbiol 9:1936
McFarland, Ross; Wang, Zi Teng; Jouroukhin, Yan et al. (2018) AAH2 gene is not required for dopamine-dependent neurochemical and behavioral abnormalities produced by Toxoplasma infection in mouse. Behav Brain Res 347:193-200
Matta, Sumit K; Patten, Kelley; Wang, Quiling et al. (2018) NADPH Oxidase and Guanylate Binding Protein 5 Restrict Survival of Avirulent Type III Strains of Toxoplasma gondii in Naive Macrophages. MBio 9:
Radke, Joshua B; Carey, Kimberly L; Shaw, Subrata et al. (2018) High Throughput Screen Identifies Interferon ?-Dependent Inhibitors of Toxoplasma gondii Growth. ACS Infect Dis 4:1499-1507
Brown, Kevin M; Long, Shaojun; Sibley, L David (2018) Conditional Knockdown of Proteins Using Auxin-inducible Degron (AID) Fusions in Toxoplasma gondii. Bio Protoc 8:
Hakimi, Mohamed-Ali; Olias, Philipp; Sibley, L David (2017) Toxoplasma Effectors Targeting Host Signaling and Transcription. Clin Microbiol Rev 30:615-645
Peyron, Francois; Mc Leod, Rima; Ajzenberg, Daniel et al. (2017) Congenital Toxoplasmosis in France and the United States: One Parasite, Two Diverging Approaches. PLoS Negl Trop Dis 11:e0005222
Wang, Zi T; Verma, Shiv K; Dubey, Jitender P et al. (2017) The aromatic amino acid hydroxylase genes AAH1 and AAH2 in Toxoplasma gondii contribute to transmission in the cat. PLoS Pathog 13:e1006272
Shen, Bang; Brown, Kevin; Long, Shaojun et al. (2017) Development of CRISPR/Cas9 for Efficient Genome Editing in Toxoplasma gondii. Methods Mol Biol 1498:79-103
Jones, Nathaniel G; Wang, Qiuling; Sibley, L David (2017) Secreted protein kinases regulate cyst burden during chronic toxoplasmosis. Cell Microbiol 19:

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