Do Tapeworms Cause Colic? Age-Old Question Remains Unanswered

Further complicating the debate regarding whether or not the equine tapeworm Anoplocephala perfoliata causes colic in horses, Canadian researchers did not find evidence of a significant association between A. perfoliata infection and the colics seen on a day-to-day basis by veterinarians.

This is in contrast to previously published studies that have looked at the association of the parasite with specific types of colic.

A. perfoliata is a common intestinal parasite of horses that is transmitted by a fecal-oral route via an intermediate host (the oribatid mite) that lives in pasture. Worms are 4-8 cm in length and attach to the wall of the intestine, primarily around the ileoceal junction.

"Case reports and epidemiological studies have suggested that A. perfoliata infections can cause colic, intussusception, and rupture of the cecum," explained Andrew Peregrine, BVMS, PhD, DVM (Hons) Glasgow, Dipl. EVPC, MRCVS, from the Department of Pathobiology at the Ontario Veterinary College in Canada. "We performed this study to determine if an association existed between A. perfoliata infections and risk of colic in Ontario horses."

Tapeworms in a horse


Researchers collected data from 234 horses residing in Southern Ontario. Of the horses, 117 had been diagnosed with colic by local veterinarians, while the remaining 117 horses were from the same stable as the colicky horses and matched for age, breed, and gender when possible.

In contrast to previous studies carried out in the United Kingdom, no evidence of a statistically significant association between a positive blood test for A. perfoliata and colic existed.

According to Peregrine, differences in study design, definition of colic, selection of case and control horses, and climate differences between Canada and the United Kingdom are thought to play a role in the apparent incongruities between the available studies.

"Our results do not rule-out tapeworms as an important cause of certain types of colic in horses. Furthermore, in light of the variation in climate across North America, more research is necessary elsewhere in Canada, and the United States, to determine whether our findings are applicable to horses outside southern Ontario," emphasized Peregrine.

One problem associated with detecting tapeworm infections is the fact that the traditional fecal test is notoriously insensitive. As a result, Peregrine and colleagues used a blood test that is considered to be more accurate.

"Over half of the included horses (56%) were diagnosed with tapeworm infections based on a blood test, whereas only 6% of the horses had tapeworm eggs in their feces," said Peregrine.

The blood test, currently available in the United Kingdom only, will be available in Canada and possibly the United States in the near future.

For more details, the full-length article, "Occurrence of Anoplocephala perfoliata infection in horses in Ontario, Canada and associations with colic and management practices," is available in the April 2008 edition of Veterinary Parasitology.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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