Ask the Vet: Internal & External Parasites

Question: I have a companion donkey. My horse contracted lungworm. Do you believe horses and donkeys can be kept together?

Answer: Lung worms are a pretty unusual problem in horses in the United States. When they do get infected, it is usually from donkeys. Donkeys infected with lung worms usually show no clinical signs of disease. In horses, the parasites only very rarely can complete their life cycle, so the transmission almost never goes the other way.

It’s harder to make a definitive diagnosis of lungworms in horses than it is in donkeys. With donkeys, diagnosis can be made with a fecal test, but that generally doesn’t work in horses.

Question: Everything I have researched says to not deworm regularly anymore and perform fecal counts first. That said, we now do fecal counts twice a year. What is your opinion on this?

Answer: I think what you’re doing is great. Checking twice a year, and deworming only the moderate and heavy shedders is certainly the way to go. It’s better for the horses, and it’s better for the environment, too!

Question: My horse is perfectly fat and healthy, but on her neck and chest she has a lot of dry skin hanging. Her mane is still thick. Could this be parasite related?

Answer: While “dry skin hanging” doesn’t bring any condition immediately to mind, there are certainly parasite problems, both internal and external, that can result in skin-related problems.  Of course, there are also many skin problems that aren’t related to parasites, and it’s not always easy to tell the difference between those that are and those that aren’t. This sounds like the sort of thing that you should have your veterinarian look at, to see if you can come up with an underlying cause.

Question: Because “pinworms” do not show on fecal tests, what is the best way to make sure my horses do not have pinworms and how can I keep them from getting them? If they have pinworms, what is the best way to get rid of them.

Answer: Pinworms are bothersome parasites that cause very little actual damage to the horse.  But while they’re not dangerous, they can certainly be a pain in your horse’s butt.  Adults crawl out of the horse’s rectum to lay their eggs, which can cause intense itching.

Severe itching and hair loss can be a sign that a horse has pinworms.  Occasionally you can make a diagnosis by seeing adult pinworms around the rectum.  The test for pinworms is the “Scotch tape” test, where you touch the sticky side of cellophane tape around your horse’s anus, and see if it picks up eggs, but that test doesn’t always find eggs.

Common orally-administered deworming agents such as ivermectin or pyrantel still have pretty good effectiveness against pinworms, even though resistance to such agents is reported.  I’ve heard of some people putting deworming paste in rectally, as well, in an effort to increase the local concentration of dewormer (but I have no idea if it’s effective).

Prevention of further infection also relies on devoting time to keeping your horse’s rear end clean.  You should also decontaminate areas where horse’s might rub (and leave eggs) such as fence posts, walls or other surfaces.  Use a wire brush and a safe disinfectant.  Of course, keep feed and water sources cleaned out, too (which you’d want to do anyway, of course).