Extremely large numbers of tapeworms can cause intestinal obstruction. It’s also believed that irritation caused by these parasites can lead to spasmodic or gas colic. In rare cases, tapes have been suspected of causing intussusception, a telescoping of one segment of bowel into another that can require surgery. Colic issues aside, tapeworms can do a lot of damage to the intestinal lining at their attachment sites.
Move Over Bloodworms.Until the appearance of effective, safe and easy paste dewormers, the most dangerous parasite was Strongylus vularis, the large Strongyle or ”bloodworm.” These parasites invade the wall of the intestine when in their immature form, causing extensive scarring. They also travel inside the arteries to cause damage and clot formation in the arteries feeding the intestine and the even the hind legs. They were the most common cause of colic, but they’ve been virtually eliminated.
Many believe the role of tapeworms in colic has become clearer now that bloodworms are out of the picture. It’s also possible that the older deworming drugs that contained organophosphates were keeping tapeworms under control. Once that this potentially toxic type of drug was no longer used, tapeworms went virtually uncontrolled for a long time.
After reports began to appear suggesting that tapeworms might pose a colic risk, researchers became more interested in this parasite. A nationwide survey published in 2003 found that from 50 to 80% of horses tested in the Eastern and Midwestern states had evidence of tapeworm exposure, while new data showed from just under 20% of California horses had tapeworm exposure, 36.5% in Oregon and 25.3% in Washington.
Unfortunately, it’s not that easy to determine if your individual horse is harboring tapeworms. A blood test for antibodies is available, but antibodies don’t necessarily mean current infection. Fecal flotations aren’t helpful because the eggs are laid in ”rafts” called proglottids, which are actually sloughed body segments of the tapeworm that are packed with eggs. With heavy infections, you may see these shed proglottids in the manure, where they look like short, wide white ribbons. On close inspection, you can see them moving. However, this is rare, probably because of the large volume of equine manure. The proglottids are much heavier than single eggs and will not float in the flotation fluid. Special techniques can be done to attempt to recover them, but even this isn’t always successful because the tapeworm isn’t necessarily always releasing proglottids.
We don’t know too many details about the life cycle of tapeworms in horses either. We don’t know how long they take to mature inside the horse, or how long they can live in the horse. It’s known that the horse becomes infected after eating a tiny soil mite called an oribatid mite. These mites live in the upper layers of the soil, under moist conditions, and their job is to degrade organic material like manure. In the process they pick up tapeworm eggs. The eggs then mature to an infective stage within the mite.
Although it’s theoretically possible for horses to become infected eating hay or grain contaminated with soil, it’s grazing horses that are at highest risk of tapeworm infection. The more grazed down the pasture, the higher the risk.
Bottom Line.Double-dose pyrantel pamoate (Strongid) or Farnam’s recently introduced TapeCare Plus, which also contains pyrantel pamoate in a tapeworm-effective dose, are effective in removing tapeworms, but some studies show a rise in egg production again after two weeks, which disappears after a second treatment at that time.
Daily pyrantel tartrate, as found in Strongid C and other brands of daily dewormer, was also effective in at least stopping egg release from tapeworms. The newest addition to the tapeworm arsenal is praziquantel, which is sold in combination with either ivermectin (Equimax or Zimecterin Gold) or moxidectin (Quest Plus). The ideal deworming interval for controlling tapeworms is unknown, but the most common recommendation is to treat mid spring and late fall.
Article by Veterinary Editor Eleanor Kellon, VMD.