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Monday, August 15, 2005

Tapeworms Recently Found to Pose Risk to Horses

Source: Dr. James Brendemuehl, August 15, 2005

An archive of pet columns from the University of Illinois College of Veterinary Medicine is on the Web at http://www.cvm.uiuc.edu/petcolumns/.

Summer grazing increases horses' exposure to internal parasites, since infectious eggs and larvae can thrive in contaminated soil and grass. According to Dr. Jim Brendemuehl, equine Extension veterinarian at the University of Illinois Veterinary Teaching Hospital in Urbana, recent research has uncovered a previously unrecognized menace. Joining the list of pesty equine parasites that includes nematodes, small and large strongyles, roundworms, pinworms, and bots is a problem usually associated with dogs and cats: tapeworms.

Until recently, the significance of tapeworm infestation in the horse had gone unnoticed because of the lack of a routine diagnostic screening test. The best way to determine tapeworm infection was through direct examination of the gut, either through surgical or post-mortem examination, and these tests are not commonly performed. Fecal examinations, though simpler to perform, are not very accurate.

Fortunately, a new screening test has been developed that detects antibodies that horses produce when infected with the most common tapeworm found today, Anoplocephala perfoliata. When researchers used this test to survey the incidence of tapeworm exposure in U.S. horses, they detected tapeworm infections in all areas of the country. Horses in the upper Midwest showed the highest level of exposure, with over 95 percent of horses tested having antibodies against tapeworms.

A. perfoliata averages only an inch in length, but since these worms frequently accumulate in large numbers, they can cause significant infections. Tapeworms inhabit specific areas of the intestine, and this species inhabits the ileocecal junction, where the small intestine joins the large intestine.

Dr. Brendemuehl warns that tapeworm infections may bring an array of intestinal complications. When tapeworms attach to the intestinal wall, they can cause severe local inflammation, resulting in scarring and thickening of the intestine wall. Excessive thickening and scarring can affect the digestive and absorptive functions of the intestine.

"Large numbers of tapeworms in the intestines may also increase the risk of serious intestinal injuries, such as ileocecal intussusception, in which the small intestine pushes itself into the wider large intestine, and ileal impactions, in which the worms block the intestine," notes Dr. Brendemuehl. "Both of these complications may require surgery. Tapeworms can also interfere with normal intestinal motility and greatly increase the risk of spasmodic gas colic."

Treatment of equine tapeworm infections has recently become easier with the introduction of a new class of pharmaceuticals that are highly effective against tapeworms. The compound praziquantel, which has long been used to treat tapeworms in dogs and cats, has just been approved for use in horses in combination with either ivermectin or moxidectin, more traditionally used broad-spectrum anthelmintics and boticides. Since praziquantel is new to the equine parasite population, tapeworms should not be resistant to the drug.

Dr. Brendemuehl recommends adding these newly approved anthelmintics to an arsenal against internal parasites, citing their nearly 100 percent efficacy and high margin of safety.

For more information about equine tapeworm infections, consult your equine veterinarian.

Veterinary Extension/Office of Public Engagement University of Illinois College of Veterinary Medicine 217/333-2907

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