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United States Department of Agriculture

Agricultural Research Service


item Lichtenfels, James
item Hoberg, Eric
item Zarlenga, Dante

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/31/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Veterinarians and parasitologists routinely determine the intensity of gastrointestinal nematode infections based on counts of eggs in feces. Unfortunately, the eggs of the most important pathogens cannot be identified even as to genus and existing identification keys to free-living larval stages (which can be cultured from fecal eggs) are out-dated, time-consuming and extremely difficult to use. These constraints on the direct identification and assessment of intensity of infection in individual herd animals often require the introduction of sentinel, naive animals to the pasture for specific periods after which they are sacrificed so adult nematodes, which are much easier to identify, can be obtained from the digestive tract. Progress in the morphological identification of individual specimens of either sex of many trichostrongyloids and the development of molecular techniques for identifying fecal eggs has provided methods that make possible the determination of which individual herd animals should be drug-treated. In the future, directly determining the identity and intensity of infection for specific pathogens in individual animals will become routine and will have significant advantages including the selective treatment of only individual hosts with heavy infections of known pathogens. This should reduce the cost of controlling the parasite, lessen any environmental impact of the drug and greatly reduce the chances for development of drug resistance in the nematode populations.

Technical Abstract: The systematics of trichostrongyloid nematodes of ruminants provides the foundation for diagnostics and responds to the need to identify eggs in feces, free-living larvae from pastures or fecal cultures and larval or adult nematodes collected from hosts. These needs are associated with diagnostic problems or research projects. Difficulties in identifying all developmental stages of tricho- strongyloid nematodes of domestic ruminants still severely limit the effective diagnosis and control of these parasites. Phylo- genetic hypotheses as the basis for predictive classifications have been developed only for the subfamilies of the Trichostrongy-lidae. Modern systematic methods have not yet been applied to the develop- ment of classifications for all subfamilies and most genera of the Trichostrongyloidea. Additional factors complicating the above problems are a lack of knowledge of the parasites of wild bovids and cervids, the international transport of wild and domestic hosts and environmental changes that alter the parasite fauna in domestic ruminants. Significant progress toward the development of DNA probes for identifying fecal eggs has been reported. This report briefly describes recent progress in the development of improved tools for identification, phylogenetic analyses and predictive classifications. It also describes future research needed on the identification and classification of trichostrongyloid nematode parasites of domestic ruminants. Nematodes included are species of the superfamily Trichostrongyloidea known to be important pathogens of domestic ruminants

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