The weird world of the gender-bending tapeworm


In episode 5 of “The Parasite Journey of the Horse”, equine parasitologist Martin Nielsen takes a “complete shift of gears” and checks out flatworms or tapeworms. These nasties look different to the previous worms in the series, and have some different biologies.

“There are three kinds of tapeworms that horses can get. One is common and the two others are really rare. The one your horse is likely to encounter in its life is Anoplocephala perfoliata,” Nielsen says.

A cluster of tapeworms in the intestinal tract of a horse. © Gluck/The Parasite Journey of the Horse

Tapeworms are unique from other equine parasites in a couple of ways; these baddies are hermaphrodites, meaning they are both male and female at the same time and can self-fertilise. They also use an intermediate host. For horses, this is the dung mite, which accidentally picks up the tapeworm egg. The horse then ends up eating the mites while grazing, because they’re everywhere.

“If there’s grass, there’s going to be tapeworms,” Nielsen says.

“Mites like a moist and lush environment, which is the kind of environment that makes the grass grow. And when you have a bit of length to the grass, there’ll be some moisture retained in between the grass blades, and that’s where the mites like to crawl around.”

But the prevalence is variable among a herd of horses; just because one horse on a farm has it, it doesn’t necessarily mean the next horse has it. “On average, 50% of horses would be expected to have tapeworms.”

Dr Martin Nielsen with adult tapeworms Anoplocephala perfoliata. The sample came from one horse, who was completely healthy, Nielsen says.
Dr Martin Nielsen with adult tapeworms Anoplocephala perfoliata. The sample came from one horse, who was completely healthy, Nielsen says.

The video looks at the problems tapeworms can cause, including ileum impaction and “telescoping” which overworks the intestine as it tries to work past the impaction, and colic. Deworming can help minimise this risk. The good news is there is no known drug resistance to tapeworm. Products with the active ingredients of pyrantel and praziquantel are the recommended treatments.

Neilsen also shows viewers the long, slender looking variety which is very rare, the Anoplocephala magna is where the name “tapeworm” derived.

Watch the video to learn more!

• We recommend watching the series in order:
Episode 1: Foal parasites
Episode 2: Ascarids, or roundworms
Episode 3: Small strongyles (cyathostomins)
Episode 4: Bloodworms
Episode 5: Tapeworms
Episode 6: Bots
Episode 7: Pinworms

See also: the inside secrets of “Creepy Crawlies”.

» For more from Dr Nielsen, check out his short video series on parasite control, starting here.

Martin K Nielsen

Dr Martin Nielsen is a professor in equine parasitology at the Maxwell H. Gluck Equine Research Center at the University of Kentucky. » Read Martin's profile

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