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Illinois Livestock Trail
Tapeworms Pose Summertime Risk to Horses
by Dr. Jim Brendemuehl, Equine Extension Veterinarian, Univ. of Illinois College of Veterinary Medicine

Most horse owners know that summer brings flies and mosquitoes, which in turn bring the risk of infection with Eastern equine encephalomyelitis and West Nile virus. By now, horses should have received annual boosters. Foals born in 2005 should begin the vaccination cycle at age 3 to 4 months.

Summer grazing also increases exposure to internal parasites. In addition to the well-known menaces--nematodes, small and large strongyles, roundworms, pinworms, and bots--a new threat has been uncovered through recent research: tapeworms.

Three species of tapeworms have been shown to infect horses in North America. Tapeworms inhabit specific areas of the intestine. The most common tapeworm found today, Anoplocephala perfoliata, averages only about an inch in length, but frequently accumulates in large numbers. This tapeworm inhabits the ileocecal junction, where the small intestine joins the large intestine.

The significance of tapeworm infestation in the horse had gone unnoticed because of the lack of a routine diagnostic screening test. Fecal examinations do not give accurate representations, so the definitive way to determine their presence is direct examination of the gut, either during surgery or at necropsy. The most thorough necropsy investigations, which were done in Kentucky, revealed an infestation rate of 53 percent to 64 percent.

A new screening test that detects antibodies to A. perfoliata has recently been used to survey the incidence of tapeworm exposure in the United States. While tapeworm infection was detected in all areas of the United States there was a wide range of regional exposure. Horses in the upper Midwest had the highest level of exposure, with over 95 percent of horses tested having antibodies.

Many medical problems are believed to be associated with the presence of tapeworms:

  • The attachment of tapeworms in the intestine is associated with severe local inflammation resulting in local scarring and thickening of the intestine wall.
  • High tapeworm burdens are associated with serious clinical manifestations, such as ileocecal intussusception or ileal impactions, both conditions that commonly require surgical intervention.
  • Tapeworms appear to interfere with normal intestinal motility.
  • Horses with tapeworms are eight times more likely to experience spasmodic (gas) colic than are uninfected animals.

Minimizing equine tapeworm infections has recently become easier with the introduction of a new class of anthelmintics that are highly effective against tapeworms. The compound praziquantel, which has been used for years to treat tapeworms in dogs and cats, has recently been approved for use in the horse in combination with either ivermectin or moxidectin, both broad spectrum anthelmintics and boticides. Since these compounds are new to the equine parasite population, there should be no issues with drug resistance. Additional benefits include almost 100 percent efficacy and a high margin of safety, making these products a valuable addition to our arsenal against internal parasites. I have implemented a spring and late fall rotation with my personal herd.

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