If you’ve gone over the 2013 AAEP Guidelines (CLICK HERE to see my summary), you’ve probably (hopefully) gotten the idea that instead of just deworming all the time, it’s a good idea to do periodic fecal eggs counts to see how badly – or if – you horse is affected by parasites prior to deworming him. But no matter how closely you adhere to those guidelines, one question still nags. “What about all those other worms, you know, the ones where fecal egg counts may not be as useful?” This article is about those other bad boys: tapeworms, bots, ascarids, and pinworms.
These “other” worms are a bit different than the worms for which fecal egg counts typically recommended. For one, they have different life cycles. For two, they don’t lay very many eggs, and fecal counts aren’t that useful for finding them. But they occasionally have some health implications for horses, and I figure you should know about them. Here goes.
BOTS (Gasterophilus spp.)
Mostly, bots are icky (that’s a medical term) and annoying. But they are rarely associated with any real health problems for horses, although it was reported way back in 1938 by some Hungarian veterinarians…
CLICK HERE if you want to read about them, which I did, mostly because I haven’t met any Hungarian veterinarians.
… that when bot flies get in the horse’s rectum, they can cause itching, straining, colic, increased frequency of defecation, and even prolapse of the rectum (essentially, it turns inside out). Even so, as icky as they are and with the occasional documented health problem, you don’t necessarily have to make yourself crazy trying to get rid of them. That said, I do think it’s a great idea to clip the hair off you’re horse’s lower legs, or scrub, scrub, scrub to remove bot eggs, because by doing that, you can help prevent infections, and well, just keep the overall yuck factor down.
Most commonly, people recommend treating for bots once a year, in the late fall or early winter, or, as is commonly said, 30 days after the first frost. Ivermectin and moxidectin work great, and when you clean them out with the dewormer, you get the benefit of helping to decrease transmission in the following year, too. Plus, you get to of kill a bunch of other worms, too (as long as they aren’t resistant).
TAPEWORMS (Anoplocephala perfoliata – say that fast three times)
Nobody really paid much attention to tapeworms in horses until a bit more than a decade ago, when it was reported that tapeworms can colic in horses, and several studies, in places like Sweden and the Netherlands have concluded that there’s probably an association. But how big a problem it really is is still a matter of discussion in the veterinary parasitology community (these are not discussions that you want to miss Family Guy for, I promise you). Still, most of the times when horses colic as a result of tapeworms, it’s because they have pretty heavy parasite loads; on the other hand, most of the time horses have tapeworm infections, they don’t carry very many worms, and those worms that are there don’t really do much harm.
If you do get a positive test for tapeworms in your horse, deworming products that contain the drug praziquantel, or a double dose of pyrantel pamoate are the way to go. Since infections are so difficult to diagnose, a single annual treatment after it gets cold (like with bots – and there are combination products that kill both – may not be a bad idea, especially if you’re horse lives in a moist pasture. If your horse lives where it’s dry, and you’re worried, you might want to have a serum test done. If your horse had a low or a negative titer, you could sleep easy, and not worry about treating him for tapeworms.
PINWORMS (Oxyuris equi)
Pinworms are a pain in the rear, and, yes, I’m making a pun. Pinworms aren’t all that common, and they don’t really cause serious health problems in horses, but when they cause problems, the horses go nuts. That’s because in the more severe cases, when the adult worm crawls out of the rectum and lays its eggs on the horse’s backside (this is not a pretty image, I admit), the eggs can cause an intense itching. This doesn’t happen to all horses – some horses can have pinworm infections and seem not to be bothered in the least.
When infected horses rub, they spread their eggs around to walls, feeders, or anything else they can rub on, and parasite transmission occurs by contact with such surfaces, as well as through contact with brushes, tail wraps, and the like. The eggs are pretty tough, too, and they can last in the environment for a long time.
Pinworm eggs don’t commonly show up in fecal exams, either. The more sensitive tests are the “Scotch Tape Test,” where you wrap your fingers in scotch tape, sticky side out, and see if you can get some eggs on the tape (in the same manner that you’d use a lint roller on clothes), or scrapings of the area around the horse’s rectum.
There are reports of resistance by pinworms to most of the deworming agents, but most of the common dewormers are pretty effective. In some cases, veterinarians may even put deworming pastes directly into the rectum, to try to get higher levels of dewormer concentrated in the area of infection. But don’t just rely on deworming – take the time to thoroughly scrub your horse’s backside to remove any eggs that the female worm may deposit (and then wash the things that you used to wash your horse with, too, with soaps or disinfectants).
ASCARIDS (Parascaris equorum)
The importance of ascarids in young horses, and their rapid life cycle, and their low level of egg shedding, is why many folks may choose not to bother with doing fecal exams on foals, particular in situations where there a lot of them (foals). And while ascarids can occasionally be seen in adults, ascarid infections are pretty darn rare, mostly because adult horses become immune to them.