Visiting Vet: Intestinal parasites

They can be lurking in many places.


Bubbie the beagle was in recently for her annual physical exam, which routinely includes sending a stool sample to the laboratory to test for evidence of common intestinal parasites. Worms like hookworms, roundworms, whipworms, and tapeworms, and protozoan parasites like giardia, toxoplasma, and coccidia. The Companion Animal Parasite Council (CAPC), an independent council of veterinarians, veterinary parasitologists, and other animal healthcare professionals, publishes guidelines for veterinarians about all things parasitic. CAPC recommends veterinarians conduct such fecal examinations at least “four times during the first year of life, and at least two times per year in adults, depending on patient health and lifestyle factors.” Honestly, in well-cared-for, healthy, adult pets getting regular veterinary care, with no history of previous parasitic infections or increased risk factors, I am usually content checking once a year.

Bubbie certainly fits that category. Eight years ago, as a newly adopted rescue pup, she arrived with a hookworm infection that took several courses of treatment to eliminate, but since then, her fecal tests have all been clear. So her mother was particularly surprised when I called with the news that the laboratory had identified two different types of roundworm eggs in this year’s specimen. The owner commented that she had not seen worms in the sample, or in any of Bubbie’s poops, for that matter. “They must be microscopic,” she said.

Well, yes and no. All the intestinal worms that commonly infest dogs in our neck of the woods are visible to the naked eye. Why can’t you just peek at pups’ poop to diagnose parasitic infections, rather than spending money on lab tests? Because, with the exception of tapeworms, which periodically pass small, white segments in the feces, all these other worms stay safely hidden inside. The laboratory looks for the worm’s microscopic eggs … but if all the worms are one sex, or very young, or very old, they may not be laying eggs. Thus, absence of microscopic eggs does not necessarily mean absence of worms. The lab then does a second test, looking for proteins that leech off the surface of adult worms into the poop.

Bubbie’s test results were confusing. Despite the presence of many roundworm eggs, the lab did not find antigen in the sample confirming the presence of adult worms. How could Bubbie be passing worm eggs while not testing positive for adult worms? I posed this question to the laboratory veterinarian. She explained. Sometimes in the early stages of infection, young adults are laying eggs but not shedding enough protein themselves to yield a positive antigen test. Even if the adult worms are shedding lots of antigen, it does not necessarily get evenly dispersed throughout the sample. Thus, it is possible to get a “false negative” if the specimen we collected just happened to be a piece of the log without dispersed antigen.

The third possibility was one which could mean that Bubbie might not actually be infected with adult roundworms at all. Coprophagy. That means eating … well … you know … poop. If Bubbie ate another animal’s feces, and those feces contained roundworm eggs, those eggs could conceivably pass right through her … in one end and out the other. We see this often with dogs who ingest bird, rabbit, and deer droppings, but in these cases the laboratory can often tell us that the eggs (or protozoa) found are not a parasitic species known to infect dogs. Then we can ignore those findings.

In Bubbie’s case, however, the species of roundworm eggs found certainly can infect dogs. Dogs contract infections by consuming worm eggs in soil, often by licking their paws. They can also be infected by eating rodents. Puppies can acquire roundworms in utero, or after birth by nursing on an infected mother. There is one type of roundworm that infects only dogs, one type that infects only cats, and one type that can infect both. Depending on the age and health of the dog, symptoms may include diarrhea, vomiting, a potbellied appearance, and general poor condition. Rare but more serious consequences may include intestinal obstruction, pneumonia, even death … but quite often there are no signs at all to indicate the presence of the worms.

Bubbie’s owner had not seen her dog hunt rodents or eat feces. The family used to have several cats, but these passed away years ago. How could the beagle have contracted roundworms?

Here’s how. One female roundworm can lay 100,000 eggs in one day. Those eggs can persist in the environment for years, even in harsh weather conditions. Bubbie may have been exposed to soil contaminated ages ago by the family cats, or more recently by wildlife, or by feral or neighborhood cats. She may have eaten the remains of an infected dead mouse. In any case, treatment was indicated, not only for Bubbie’s well-being but because some species of roundworms can infect people, causing serious illness ranging from intestinal upset to blindness.

Now don’t panic and banish your dog from the house. People do not get infected with roundworms from normal contact with their pets. Infection requires ingestion of parasite eggs. This occurs most commonly in children, who may not be careful about washing dirty hands before eating or putting their fingers in their mouths. Other things that increase risk of human infection include animals defecating in play areas, children’s sandboxes, and gardens. Preventing animal access to such areas is useful. So is practicing good hygiene. Wash your hands. Wash your kid’s hands. Wash your garden fruit and veggies.

We prescribed deworming medication for Bubbie to take now and again in two weeks. This second course is recommended to be sure to clear all life cycle stages of the roundworm. We advised cleaning up Bubbie’s feces to prevent her from reinfecting herself by contact with her own waste. Her owner will bring specimens for us to recheck several times after finishing treatment, to confirm that we can give Bubbie a clean bill of health. OK. I’m pooped now. I think I’ll go wash my hands.