Venter Institute, International Team of Researchers Publish Paper Outlining Key Genes in Toxoplasma gondii Strains that Contribute to Virulence

T. gondii, one of the most prevalent parasites affecting mammals, infects more than 1 billion people worldwide

(LA JOLLA, CA)—February 11, 2016—The J. Craig Venter Institute (JCVI) researcher Hernan Lorenzi, Ph.D., in collaboration with L. David Sibley, Ph.D., Washington University School of Medicine, and a team of international researchers have published a paper outlining key genetic differences in strains of Toxoplasma gondii which shed light into the biological and virulence differences between T. gondii strains and between other closely related parasites. The paper, published January 7th in Nature Communications, involved 32 international researchers including corresponding authors Drs. Lorenzi and Sibley.  

T. gondii is a tissue-cyst forming parasite that is one of the most prevalent in the world. It affects about 50 million people in the United States, more than 1 billion worldwide and many wild and domesticated animals. Although most people living with the parasite can lead normal lives, for those who are immune compromised, infection can be deadly. The work to better understand T. gondii’s biology and virulence will help researchers improve methods to control the parasite.

Strains of T. gondii from countries worldwide were contributed for the study by the team, including parisitologist Jitender Dubey with the USDA Agricultural Research Service in Beltsville, Md. The consortium of authors conducted a genomic analysis on each of 62 T. gondii strains.

The team compared the genomes of the global T. gondii strains to several closely related parasites, and found novel families of proteins in the T. gondii strains called secretory pathogenesis determinants (SPDs).  These SPD proteins are key to modulating the host animal’s innate immune response, allowing infection. The SPD genes, some of them known to mediate host-cell attachment, modification of host immunity and immune evasion, frequently presented copy number variations across strains or were found amplified in tandems forming gene arrays. The expansion of parasite-specific SPDs was the main feature that distinguished T. gondii from its closest relatives, Hammondia hammondi and Neospora caninum, which are not human pathogens.

The study also revealed that the co-inheritance among major clades of T. gondii of large haploblocks enriched in clustered SPD genes shapes the population structure of this parasite and might determine host range, transmission and pathogenicity. The study included highly virulent strains from jungle regions in Brazil and French Guyana, milder strains collected from farms in the United States and other strains from Europe, China and Africa.

According to Dr. Lorenzi, “The significant amount of genome sequencing data generated by this project provides, for the first time, a better picture of T. gondii worldwide diversity at the genome scale and sheds light into the genetic factors that contribute to differences in the biology and virulence of T. gondii strains.

Dr. Sibley added, “Identification of important pathogenesis determinants on a genome-wide level will foster mechanistic studies on the function of key parasite virulence factors and help to improve diagnosis and treatment of toxoplasmosis.”

Funding for this work came from grants from the U.S. National Institute of Allergy and Infectious Diseases, the National Institutes of Health and the Department of Health and Human Services, as well as the Canadian Institutes of Health.

About J. Craig Venter Institute

The JCVI is a not-for-profit research institute in Rockville, MD and La Jolla, CA dedicated to the advancement of the science of genomics; the understanding of its implications for society; and communication of those results to the scientific community, the public, and policymakers. Founded by J. Craig Venter, Ph.D., the JCVI is home to approximately 200 scientists and staff with expertise in human and evolutionary biology, genetics, bioinformatics/informatics, information technology, high-throughput DNA sequencing, genomic and environmental policy research, and public education in science and science policy. The JCVI is a 501 (c)(3) organization. For additional information, please visit http://www.weizhongli-lab.org.

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