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Craterostomum Horse nematode

DNA Probes to Identify Horse Worms

By Hank Becker
February 5, 1998

A new set of diagnostic probes could help save horses worldwide from nematode parasites. The probes are being developed jointly by Agricultural Research Service scientists and researchers in Scotland and Australia.

As horses graze, they can accidentally swallow about 65 species of nematode parasites (worms) lying in the grass. As many as 150,000 parasites can live in the wall of a horse's large intestine. The parasites can cause death, weight loss and weakness. To prevent diseases, horse owners must routinely treat their animals with anti-parasitic drugs.

Worm resistance to anti-parasitic drugs--the only current control--is more than 50 percent in some areas. And no drugs are available to treat nematode larvae, the immature stage that causes blood loss and diarrhea when they emerge from the cysts in the wall of the intestine. Available diagnostic methods come up short. Adult nematodes can be readily identified. But this isn't possible for eggs found in samples of horse feces or larvae cultured from these eggs.

An ARS parasitologist--the world's leading expert on these worms-- is helping his Scottish and Australian colleagues develop the new diagnostic probes. The probes are based on the worm's DNA sequences. So far the researchers have developed probes to detect the adult stage of about 20 of the 65 nematode species. The scientists' ultimate goal is probes to identify egg and larval stages. With such probes, horse owners could more selectively use anti-parasitic drugs. This would reduce treatment cost and extend a drug's useful life by avoiding its overuse.

Other potential uses for the probes: help researchers determine whether a nematode is drug- resistant or is a serious pathogen; identify the predominant species causing larval cyathostomiasis, an emerging horse disease; and evaluate potential natural controls such as fungi that kill the worm larvae in soil.

Scientific contact: Ralph Lichtenfels, ARS, Biosystematics and National Parasite Collection Unit, Beltsville, MD 20705, phone (301) 504-8444, fax (301) 504-5810,

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