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United States Department of Agriculture

Agricultural Research Service

Research Project: MOLECULAR SYSTEMATICS AND COMPARATIVE POPULATION GENETICS OF PARASITIC ORGANISMS THAT THREATEN FOOD SAFETY AND SECURITY
2011 Annual Report


1a.Objectives (from AD-416)
Objective 1: Employing single-gene and genomic approaches, improve diagnosis of protists and nematodes that parasitize major food animals and that facilitate establishment, internalization, and survival of bacterial pathogens in produce.

Subobjective A: better characterize the molecular epidemiology of parasitic coccidia and trichinella.

Subobjective B: better characterize those bacterophagous eukaryotic microbes that may convey and help establish in produce pathogenic bacteria.

Objective 2: Develop a molecular phylogeny of coccidia in fish in order to better define their potential risk to food safety and security, and in order to better understand the relationship between Eimeriidae (including the agents of avian coccidiosis) and the Sarcocystidae (including the agent of human toxoplasmosis).

Objective 3: Better define the historical and ongoing interactions among wildlife and livestock reservoirs of Toxoplasma gondii through comparative population genetic analysis.


1b.Approach (from AD-416)
Several genes will be sequenced from parasites obtained from a wide array of animals, both domesticated and wild. These will be compared to each other, and to sequences obtained from human beings, in order to define the diversity and epidemiology of these parasite species. Homologues will be characterized for genes whose global variation has already begun to be studied in T. gondii, including the Intergenic Spacer sequence between rRNA genes, beta tubulin introns, and others. Characterization of microsatellite alleles will be considered as a second approach which, although requiring a greater investment of time and resources, should provide greater population genetic resolution than is possible with current loci.


3.Progress Report
This is the final report for this project which has been replaced with a new project 1265-42000-016-00D. All planned experiments were completed prior to the termination date of the project. Over the life of the project, the lab determined the extent and structure of genetic variation among isolates and epidemic strains of Toxoplasma gondii; determined criteria for recognizing a fourth major lineage of Toxoplasma gondii in several species of wildlife in North America; established similarities and differences between the molecular epidemiology of Toxoplasma gondii and related species of coccidia including species of Sarcocystis and Besnoitia; identified a chromosomal variant of Toxoplasma gondii which occurs with uncommon frequency in an unusually uniform state and may encode elements responsible for epidemic spread; improved methods for diagnosing these foodborne zoonotic parasites; sequenced the genomes of two isolates of the foodborne bacterial pathogen Listeria monocytogenes; demonstrated the utility of massively parallel sequencing methods to characterize the mitochondrial genomes of Trichinella spiralis and Trichinella murrelli, established and applied tools for elucidating the molecular epidemiology of Trichinella spp., documented that Trichinella spiralis did not occur in North America until its introduction from Europe, showed that this parasite is appreciably uniform throughout North America, South America, and Europe (but is more diverse in Asia, where it likely originated), developed molecular phylogenies for coccidia in fish and elucidated their evolutionary origins and relationships to better-known parasites in livestock and human hosts, and advanced the understanding of transmission of zoonotic parasites from livestock to people.


4.Accomplishments
1. Host range of cattle parasite Sarcocystis cruzi. Contacts between people and other animals remain an important source for new diseases. Identified means to discriminate between two closely related parasite species that occur in cattle, and showed that each may also infect water buffalo, a major livestock species in China. By improving genetic diagnosis, these efforts better enable veterinarians and public health officials to tell these parasites (which pose no risk to human health) from others (which may cause gastrointestinal disease).

2. A new widespread strain of Toxoplasma gondii. Pregnant women, their fetuses, and persons with AIDS are vulnerable to infections with Toxoplasma gondii, which may be acquired from infected meat or from contact with the feces of cats. Although new parasite genotypes can result from sexual recombination in cats, actual surveys of parasites in people and animals repeatedly encounter certain over-represented strains. A broader view of Toxoplasma gondii diversity was developed by identifying a fourth major lineage circulating in American wildlife species (but, so far, infrequent in our food animals). This work enlarges our understanding of how the parasite is transmitted in the wild, and how often such transmission encroaches on farmed animals.


Review Publications
Thompson, P.C., Rosenthal, B.M., Hare, M.P. 2011. Clonal population structures are derived from various population processes in the protistan oyster parasite Perkinsus marinus. Journal of Eukaryotic Microbiology. 11(3):598-609.

Last Modified: 10/24/2014
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