Thoroughly Vetted: The strange journey of the roundworm

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Word to the wise pet owner: Do not kiss your dog. Word to the wise pet owner: Do not kiss your dog.

It’s a rare week that I don’t see at least one dog or cat with Toxocara, commonly referred to as roundworm. It’s especially common in puppies and kittens who have multiple chances to be infected before adoption. They can catch roundworm from their mother while still in the womb, and then again through her milk. But if they dodge those chances, they can still pick it up the old fashioned way—by eating it.

Since roundworm makes its home in the intestine, it makes sense that pets might contract it by swallowing it. Eggs can be found in contaminated soil, deposited there by the stool of other cats and dogs, where it takes about a month to become infectious. Pets with a penchant for hunting can also catch roundworm directly from eating an infected prey animal, such as a mouse. Either way, you’d think that once those little critters are down the hatch, they could just grow up and get on with it.

But roundworms are all about the path of most resistance. Once they find themselves inside a suitable host, those young larvae are like tourists: They want to see the sights. The worms tunnel right through the wall of the intestine and wander pretty much anywhere they like, but they most often set up camp in the liver. They can hang out there for quite a while, but eventually they burrow all the way up into the lungs where they cause enough irritation to trigger coughing. The worms are hacked up and swallowed again, landing right back in the intestine where they started.

They took the long way around, but only now is it possible for them to grow into full-sized worms. And they really are impressive specimens. They can be several inches long, and are most often described as looking like spaghetti when pet owners find them vomited on the kitchen floor. If this happens, owners are likely to be both grossed out and distraught, but at least the diagnosis is obvious. Otherwise, veterinarians find roundworm by using a microscope to identify eggs in the patient’s poop.

Dogs and cats are each infected by their own species of Toxocara, both of which can be hazardous to humans. Once inside a person, the larvae try a similar trick of wandering through the body. But since they are programmed for non-human innards, they don’t really know how to get around. They can cause all sorts of problems as they roam, but blindness is perhaps the most gruesome. For some reason, the little creeps gravitate toward human eyeballs.

If that doesn’t underscore the importance of controlling parasites in household pets, I don’t know what would. Thankfully, roundworm is easy to treat and prevent. A variety of dewormers are safe and effective in managing the infection once identified, and monthly heartworm preventive medications also keep the parasite in check. If you’ve recently adopted a puppy or kitten, it’s especially important to get a stool sample evaluated and to complete a regular course of dewormer.

Intestinal parasites aren’t the most glamorous part of owning pets, but it’s not enough for some worms to merely be disgusting. Roundworms go out of their way to be weird, too. It’s best not to give them the chance.

Dr. Mike Fietz is a small animal veterinarian at Georgetown Veterinary Hospital.  He received his veterinary degree from Cornell University in 2003 and has lived in Charlottesville since.

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