The District Vet: Roundworms

The Most Common Parasite in Dogs and Cats

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For many of us, it may be uncomfortable to talk about, but I’m in the mood to discuss parasites. Seems like a good theme for these days. Last month’s discussion was hookworms, this month we will tackle roundworms.

Roundworms, known as ascarids, are the most common parasite in dogs and cats. They are also the worm that clients see the most often: whenever someone says, “My dog has worms in her stool,” it’s probably roundworms. Ascarids are long, tubular-shaped, non-segmented worms, which closely resemble spaghetti. Sorry. They can be seen alive in stool and in vomit, too.

There are several species of roundworms in dogs and cats. They are treated in the same manner in both species, but there are a few minor differences between dogs and cats. Toxacara canis is most commonly seen in dogs, while Toxocara cats is seen in cats. A third, Toxascaris leonina is less common, but is seen in both.

The first indication of ascarids in puppies and kittens is simple: either you see them in stool or their abdomens looks a bit swollen and as we say, wormy. We veterinary professionals assume (usually correctly) that all juveniles have roundworms. We will discuss why this is the case.

All Toxocara species eggs are passed in the stool into the environment. The eggs don’t hatch – inside the egg, a larvae forms and matures, turning into a stage L3 infective larvae in two to three weeks, depending upon temperature and humidity. Dogs and cats eat the infective egg / larvae from the environment, then the larvae hatches, migrates through the intestinal wall, liver and travels to the lungs. The larvae are then coughed up and swallowed. There they then mature into adults in the intestines. T. leonina does not migrate out of the intestines.

Puppies very frequently have ascarids. But why – they don’t eat much from the environment as neonates? Infective larvae can be transmitted from the mother to the newborn via a transmammary route. When the puppies and kittens nurse, infected larvae may be ingested, resulting in infection. They can also get the larvae while still in the uterus via the placenta. Roundworms really want to infect puppies and kittens, and they have found excellent routes for doing this.

As for clinical signs, many young animals show no signs, but others may have diarrhea, bloated tummies, vomiting, coughing, weight loss, failure to thrive, and rarely intestinal blockage and death. Kittens tend to show signs later, as cats cannot transfer larvae through the placenta.

People can be infected with ascarids from either the environment, eating unwashed fruit and vegetables, or from eating infected meat. The larvae migrate through tissues and can even enter the eye, causing decreased vision and even blindness. This is most frequently seen in children, with more cases in southern states than those in the north.

We treat all puppies and kittens for roundworms several times. For puppies, our routine heartworm preventives are highly effective for eliminating roundworms. In kittens, we use topical Revolution or oral pyrantel. It is important that the young animals be treated multiple times for this parasite.

Since the parasite is in the environment, routine deworming is essential for all dogs and any cats that go outside. Again, the typical oral heartworm preventives will eliminate the parasite. Dogs seem to be much less susceptible to roundworms as adults than puppies, so infection in adults is rare. I have not noted that to be the case in cats.

Roundworms are gross, but usually overall benign in cats and dogs, but can cause serious problems in people. Routine deworming is usually all that is needed to keep the risk levels low.

Dr. Dan Teich is the Medical Director for District Veterinary Hospital, Eastern Market. He is a Hill resident and can be seen walking to work with Dr. Brian, his golden retriever sidekick.