Equine Tapeworms Prevalent in Western States, Study Shows

New data shows tapeworm prevalence on West Coast farms as 17.3% in California, 36.5% in Oregon and 25.3% in Washington. A 2003 study in equine parasitology by Craig Reinemeyer, DVM, PhD, 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 more than 300 farms and 600 samples from across the three Western states.

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.

"This new research helps answer many questions about tapeworm prevalence in the western United States," said Bobby Cowles, DMV, MS, MBA, of 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. (See a special report on tapeworms.)

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.

Horse owners can ensure their herd is protected by incorporating a praziquantel dewormer into their deworming program. This class of anthelmintic has been proven effective against tapeworm infections and is commercially available.

Pfizer Animal Health's Equimax (ivermectin 1.87%/praziquantel 14.03%) dewormer, was recently evaluated for efficacy in 26 tapeworm-infected horses maintained for a year on contaminated pastures. The study indicated that using praziquantel proved to be 100% effective for the treatment of tapeworms. The percentage of tapeworm-negative horses gradually declined during the year after treatment, indicating a re-infection pattern that can be anticipated following treatment of horses maintained on contaminated premises. This also indicates that semi-annual treatment is recommended in endemic herds.

For additional information on Pfizer Animal Health's portfolio of equine products, visit PfizerAH.com.  

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