Most of you have likely brought a stool sample in to your pet’s annual veterinary visit, perhaps wondering in the back of your mind why it’s necessary to check a stool sample on an annual basis, especially if you have a cat or dog that spends minimal time outdoors.
Roundworms, hookworms, Giardia and coccidia are the most common intestinal parasites in our geographical region, and all but coccidia also have the potential to be zoonotic — transmissible to human beings — thus deserving special attention.
Roundworms, most specifically Toxocara canis (in dogs) and Toxocara gati (in cats), were found to be present in 1/79 (1.2%) of dogs and 1/26 (3.82%) of cats in Arlington County. Infection can occur via ingestion of infective eggs, in utero transmission (dogs only), or transmammary transmission, which is why it is seen so commonly in puppies and kittens. Infection can cause pot-bellied appearance, failure to thrive, and gastrointestinal signs; puppies infected in utero are most likely to be severely sick. Roundworm eggs are often found in soil, including houseplant potting soil (a source of infection for indoor-only cats). Children, with their propensity to put things in their mouths, are most at risk for zoonotic infection. Due to the complicated migration of roundworm throughout the body tissues upon ingestion in an inappropriate host, symptoms in humans can include visceral larva migrans and ocular larva migrans. Ocular larva migrans is a cause of retinal damage and partial blindness in children and can be mistaken for the more severe disease, retinoblastoma (cancer), resulting in an unnecessary removal of the eye.
Hookworms (Ancylostoma species.), found in 2.21% of dogs and 0.51% of cats in Arlington County, are transmitted via ingestion of infected eggs, as well as transmammary transmission; the larval stages of hookworm also have the ability to penetrate intact skin to infect their host. Hookworms suck blood from the wall of the intestinal tract and can lead to severe anemia and even death in young puppies; older dogs may show diarrhea as the primary sign. Hookworms are most often contracted by humans when they directly penetrate the skin, leading to cutaneous larva migrans.
Giardia, a protozoan parasite, is a common cause of intestinal symptoms in cats and dogs — primarily diarrhea, and less commonly vomiting, inappetence, or weight loss. According to the CAPC, 15.6% of dogs and 10.3% of cats with compatible symptoms tested positive for Giardia, though there are distinct regional differences, with infection being more common in some areas than others. Giardia is the most common intestinal parasite of humans in the U.S., causing similar gastrointestinal signs to those seen in our pets, such as diarrhea, bloating and cramping. Transmission in both humans and dogs results from ingestion of cysts shed in the feces of infected animals, typically from contaminated water. Fortunately, Giardia subspecies are quite species-specific so transmission between humans and pets is uncommon in healthy individuals. Children, elderly, or otherwise immune-deficient individuals are most at risk for transmission from an infected pet.
Coccidia (Isospora species), another protozoan parasite, though not thought to be zoonotic, is a common intestinal parasite, especially in puppies and kittens who do not have fully developed immune systems. It is also more common in pets from intense breeding, hoarding and shelter situations as it is very hardy in the environment. The most recent prevalence data from CAPC showed that Coccida was present in approximately 3% of dogs and cats in Pennsylvania (the closest state with prevalence data).
In general, pet-to-human transmission of roundworms, hookworms and Giardia can be minimized by removing feces from the environment on a daily basis and hand-washing after any potential contamination. Once in the environment, it is extremely difficult to decontaminate the environment; however, if stools are picked up immediately there is little chance of transmission to other pets and/or humans. It is also important to dispose of feces with the municipal waste, as it otherwise has the potential to contaminate water sources.
Other intestinal parasites found less commonly in our pets include whipworms (dogs), tapeworms, stomach worms, Toxoplasma (cats), and Strongyloides. In addition to your pet’s veterinarian, the Companion Animal Parasite Council is a fantastic resource for all things parasite-related.