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United States Department of Agriculture

Agricultural Research Service

Related Topics

Research Project: Molecular Genetics, Genomics, and Phylogenetics of Foodborne Zoonotic Parasites Affecting Food Safety and Public Health

Location: Animal Parasitic Diseases

2011 Annual Report


1a.Objectives (from AD-416)
1) Determine what genetic and genomic features distinguish Trichinella spiralis from Trichinella murrelli. 2) Utilize genomics to determine if microsatellite loci can be used to trace zoonotic outbreaks of Trichinella spiralis. 3) Determine the genetic features that account for the epidemic spread of certain strains of Toxoplasma gondii.


1b.Approach (from AD-416)
Investigations will be conducted to clarify how infections in wildlife influence the safety of pastured pork. Accordingly, first identify heritable differences between two related species of Trichinella, only one of which (T. spiralis) severely compromises pork safety by evading swine immunity. The other, Trichinella murrelli, predominates in North American wildlife but fails to thrive in swine. By comparing the genomes of these two parasites, the intent is to establish a basis for exploring what makes pigs so especially vulnerable to T. spiralis.

Secondly, develop the means to trace chains of transmission of Trichinella spp. Using markers which have already established the long-term dispersal history of T. spiralis (to the Americas in the pigs and rats brought by European colonists), researchers will attempt to discriminate instances of persistent on-farm transmission from sporadic introductions of T. spiralis to swine herds.

Finally, the genetics of T. gondii reproduction will be characterized. Both sexual and asexual reproduction can occur in T. gondii, and available data provide conflicting evidence as to the relative importance of each reproductive mode. These incongruous data leave in doubt whether this parasite evolves as an assemblage of distinct lineages, or whether it more closely resembles a coherent, interbreeding species. Additional data are needed to better resolve how T. gondii propagates and evolves. These results will help determine whether particular strains pose elevated food safety risk will help anticipate this parasite's evolutionary response to preventative interventions.


3.Progress Report
Progress has been made on all three objectives of this project (implemented in January of 2011), and significant new support for related objectives was procured in the form of a grant from NIFA with the objective to distinguish the genetic and genomic features that differentiate Trichinella spiralis from Trichinella murrelli, we sequenced certain housekeeping genes, introns, and non-coding sequences. These data will provide an estimate of genomic differences between the two, and will be used as a basis to determine if the Trichinella spiralis genome assembly can be used as a scaffold to interpret short sequence reads derived from Trichinella murrelli. In addition, we published a comprehensive comparison of the mitochondrial genomes of these two zoonotic parasite species. Finally, a proteomics approach was initiated to identify antigens in Trichinella murrelli that differ from homologues in Trichinella spiralis, with the intention that these may serve as a basis for differential serological diagnosis in swine. To determine if microsatellites can be used to trace zoonotic outbreaks of Trichinella spiralis, we assessed the capacity to detect mixed infections and applied these assays in an experimental evaluation of the vulnerability of swine to repeated infection (heterologous challenge). To determine the genetic features that account for the epidemic spread of certain strains of Toxoplasma gondii, we established (and published) new criteria for recognizing a fourth major lineage of this parasite in North American wildlife.


4.Accomplishments
1. Used novel genome sequencing methods to comprehensively describe differences between the mitochondrial genome of this important parasite of swine and a related parasite found in wildlife hosts. Understanding these differences will allow clearer understanding of how frequently food animals may be exposed to either of these two, otherwise indistinguishable parasite species (which however may pose very different levels of risk to human health). This work will lay a foundation for future work to assess risks posed by either parasite to the safety of pasture-raised pork.


Review Publications
Dubey, J.P., Rosenthal, B.M. 2010. Morphologic and molecular characterization of the sarcocysts of Sarcocystis rileyi (Apicomplexa: sarcocystidae) from the mallard duck (Anas platyrhynchos). Journal of Parasitology. 96:765-770.

Xiang, Z., He, Y., Rosenthal, B.M., Li, X., Zuo, Y., Feng, G., Cui, L., Yang, Z. 2011. Comparative studies confirm natural infections of buffaloes by Sarcocystis cruzi. Parasitology International. 127(2):460-466.

Last Modified: 4/18/2014
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