New Study Reveals a Rise in Equine Tapeworm Exposure on the West Coast
RELEASE: July 28, 2009
Pfizer Animal Health Shows Horses Country-Wide are at Risk for Tapeworm Infections
AUTHOR/ADMINISTRATOR: By Rebecca Pitcher
A ground-breaking study in equine parasitology, done in 2003 by Dr. Craig Reinemeyer of East Tennessee Clinical Research, uncovered the high prevalence of equine tapeworms throughout the United States. That original study indicated a lower risk of tapeworm exposure on the Pacific Coast compared to other areas of the country. To get a better representation of the prevalence of tapeworm exposure, the study was recently repeated, using over 300 farms and 600 samples from across the three Western states. New data from Pfizer Animal Health shows tapeworm prevalence on West Coast farms as 17.3% in California, 36.5% in Oregon and 25.3% in Washington.
These new figures confirm that the tapeworm poses a medical threat to horses all over the United States, not just the Eastern and Midwestern regions. Research has also shown that tapeworms can cause potentially life-threatening colic in affected horses. It’s been five years since the original study was released and many horse owners still think their horses are not at risk to tapeworm infestations in their area. This new information clearly demonstrates that all horse owners need to take an effective approach to protect their horses from tapeworms.
“This new research helps answer many questions about tapeworm prevalence in the western United States,” said Dr. Bobby Cowles, DMV, MS, MBA, Pfizer Animal Health. “Understanding the life cycle of the tapeworm, where it resides and the severe impact it can have on the horse is the first step to actively dealing with this potential medical problem.”
Research suggests that oribatid mites may be the key link to the tapeworm threat. As the intermediate hosts to Anoplocephala perfoliata
—the most common species of tapeworm infecting horses in the United States—these insects are highly prevalent worldwide. As microscopic decomposers, these mysterious mites can exist by the thousands or even millions per square meter of soil. Any horse that grazes on pastures, eats hay or is bedded with straw or wood products is likely exposed to oribatid mites, which could potentially translate into tapeworm infections.
As decomposers, mites ingest tapeworm eggs passed in equine feces. The eggs hatch inside the oribatid mites and the infective stages of the parasite, also known as cysticercoids, develop within the mite’s body cavity in about two to four months. Horses become infected with A. perfoliata
when oribatid mites are consumed along with forage. The digested mites release the cysticercoids in the horse’s intestinal tract and the immature parasites then develop into adult tapeworms that attach to the ileocecal junction, the meeting place of the small intestine and the cecum. The tapeworms mature and reproduce inside the horse. Eggs are released through the feces and the cycle starts all over again.
Active tapeworm infection is difficult for veterinarians to diagnose. There are two approaches to tapeworm diagnosis (1) coprologic (fecal) testing using a centrifugation/flotation technique, and (2) serologic testing using an ELISA format to detect tapeworm antibodies as evidence of prior exposure. Both tests can be labor intensive and a poor indication of the actual tapeworm burden in the individual horse and in the herd overall. This limitation often contributes to an underestimation of the true prevalence of tapeworm infection in a herd, which in turn can encourage negligence in tapeworm control. In many cases, horse owners will simply resort to routine deworming instead of performing a diagnostic test that can confirm active tapeworm infection. Also, horse owners may mistakenly assume that broad spectrum dewormers such as macrocyclic lactones (avermectins), such as ivermectin alone or moxidectin alone, or benzimida