Rachel Gardner, DVM, DACVIM
Internal Medicine Specialist, B.W. Furlong & Associates
Until recently, it was uncertain how much damage tapeworms caused and how many horses were infected with tapeworms. Research has demonstrated that tapeworm infection is an important risk factor for spasmodic colic and impaction colic involving the junction of the small intestine (i.e. ileum) and the large intestine (i.e. cecum). Tapeworm infections have also been associated with rupture of the small intestine and ileocecal intussusception.
Routine fecal analysis used to detect parasite eggs from Strongyles (bloodworms) and Ascarids (roundworms) will miss most tapeworm eggs. The tapeworms that infect horses are different from those species that are seen in dogs and cats. Visible tapeworm segments do not appear in horse manure even when there are high numbers of adult tapeworms in the horse’s gut. Therefore tapeworm infection often goes undetected and unsuspected. In one nation-wide study more than half the horses tested had been exposed to tapeworms with the highest exposure rates (62 – 96%) found among horses living east of the Mississippi River. In addition to colic, other signs of tapeworm infection may include general unthriftiness, recurring diarrhea, progressive weight loss and anemia. Many horses harboring a high tapeworm burden may not show any outward signs of disease.
Anaplocephala perfoliata is the most common of the 3 tapeworm species found in horses. Tapeworms require an intermediate host, called the orbatid mite, to complete their life cycle. These mites are common inhabitants of most pastures and hays. The mites ingest tapeworm eggs passed in the horse’s feces. While grazing or eating hay, horses ingest infected mites that release the juvenile tapeworms into the horse’s gut where they mature into adult worms that then produce eggs. Mites and tapeworms can be a problem year round, especially in more temperate climates. Foals as young as 2 to 4 months of age can harbor tapeworms. The age groups that seem to carry the highest levels of tapeworm infestations are young horses (6 months to 2 years) and older horses (> 15 years).
Until recently, there was no drug approved by the U. S. Food and Drug Administration for the removal of equine tapeworms. The recommended treatment used to be a double or triple dose of pyrantel pamoate (Strongid) administered orally. During the summer the new drug, Praziquantel, has been approved for the treatment of tapeworms in horses. This drug is available commercially in paste form in combination with Ivermectin. The combination product is sold under several names: Zimecterin Gold® (Merial Inc) and Equimax® (Pfizer Inc). This new drug combination should become a cornerstone of your annual deworming program and should be administered at least once a year.
This new dewormer has been approved for horses 4 weeks of age and older. Breeding stallions have been treated without adverse effects on fertility. The product is not yet approved for use in pregnant or lactating mares although safety trials are underway currently to evaluate this product in broodmares.
Please do not hesitate to discuss with one of our veterinarians how to incorporate Praziquantel into your parasite control program. If your horse has never been dewormed for tapeworms before (i.e. has never received a double or triple dose of Strongid before) please consult your veterinarian before administering this product for the first time. This is an important way to improve your horse’s general health while reducing the risk of certain types of colic!