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United States Department of Agriculture

Agricultural Research Service

Stomach Worms
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Systematics Success Stories

Molecular diagnostics and identification of large and medium stomach worms, primary pathogens of livestock worldwide.

Problem: Morphological similarity and intraspecific polymorphism for an array of significant nematode pathogens in ruminants has led to confusion regarding their evolution, classification, and diagnosis. Adequate intervention and control of large stomach worms, Haemonchus, and medium stomach worms, Ostertagia and Teladorsagia, is linked to accurate identification of parasites in bovine and caprine hosts.

Solution: Large scale analysis of a class of economically important Trichostrongyle parasites (estimated losses of $2 billion annually in the US) involving 4 genera, 10 species and over 30,000 base sequences was performed to better elucidate relationships within these parasite groups.

Among the important findings:
  • Demonstrated that H. contortus (sheep parasite) and H. placei (cattle parasite), though morphologically similar, are distinct species.

  • Provided the first genetic evidence among the medium stomach worms to validate the hypothesis that 2 morphologically distinct but genetically identical male parasites represent single, polymorphic species.
Impact:
  • Based in part on this research which was presented at the Merck, Sharp and Dome International Symposium on "Identification of Parasite Nematodes of Domestic Animals", the Food and Drug Administration now requires that results from all drug tests on Haemonchus of cattle and sheep be reported separately.

  • This same research provided groundwork for developing the only means available to rapidly diagnose infections of these parasites using mixed populations of eggs in feces.
(Contact- Dr. Dan Zarlenga, Bovine Functional Genomics Laboratory).


Last Modified: 9/14/2006
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