Parasites in pets: Understanding prevalence and perception

dvm360dvm360 June 2021
Volume 56

Parasites are common in dogs and cats and there are often misconceptions about the prevalence of parasites in adult pets.

dog scared at veterinarian

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Internal parasites are incredibly common in both cats and dogs. Because of their relative ease of transmission and high rate of occurrence, the vast majority of dogs will contract a parasitic infection during their lifetime. Although treatment with parasiticides is reasonably simple and straightforward, many pet owners are unaware of how common these infections are. If left untreated and allowed to progress, these infections can create health issues such as anemia1 or failure to gain weight2, and some pose a risk of zoonosis.3

Although most owners know that parasitic infections are possible, especially when the animal is relatively young, generally speaking, there seem to be some misconceptions surrounding their prevalence and appropriate testing. The misconceptions originate with owners and are further reinforced by veterinarians, who may be reluctant to suggest testing, which owners might perceive as superfluous.

Testing for internal parasites is common in both puppies and kittens, largely because they represent the largest category of infected pets. In fact, according to the Companion Animal Parasite Council (CAPC), samples collected from across the United States show that more than 30% of dogs under 6 months of age are shedding Toxocara canis, or roundworm, eggs.2 Most owners are aware that puppies and kittens can contract parasites, particularly roundworms, from the mother, either prenatally or via lactation after birth. Because of this, many new owners accept deworming as a normal part of puppyhood, akin to the first round of vaccinations and sterilization.

However, this prevalence presents as somewhat of a double-edged sword. Although most owners of puppies and kittens have their pets dewormed as youngsters because it’s common knowledge that many puppies and kittens “have worms,” many believe that the danger parasites present dissipates once the dog or cat reaches adulthood and that no further testing is required.

In many ways, they are correct: younger animals with immature immune systems are most at risk for parasitic infections. As veterinarians do not always offer testing for parasites, except at an annual visit (and not all annual visits include a fecal test), many owners believe that it’s prudent to test a fecal sample for worms only if the animal is presenting symptoms, such as the presence of worms in stool, or if the dog has knowingly been exposed to an infected dog (eg, at a dog care facility or an animal park).

Contrary to this standard belief system and practice, the CAPC recommends testing at least 4 times in the first year of life, and at least 2 times per year in adults, depending on patient health and lifestyle factors.2

This frequency of testing is somewhat unusual, as most adult dogs and cats are only brought into the clinic once a year for a wellness visit which is when fecal testing for parasites is most commonly conducted. Furthermore, in low-risk households (ie, a home with strictly indoor cats or dogs that are less likely to contract a parasite), many veterinarians simply would not recommend more frequent testing unless the animal presents with signs of infection.

Owners who are offered this level of testing may protest, particularly if they are aware that the dog has been dewormed, perhaps even multiple times in puppyhood, and is not presenting with any symptoms. In addition, some pet owners are unaware of the symptoms of intestinal parasites save for the presence of worms in the feces and may not know that their pet requires treatment in the early stages of infection.

The notable exception to this trend is Dirofilaria immitis, also called heartworm. Dog owners have long been conditioned to regularly test for and guard against heartworm using monthly preventives. It has become standard practice to test for heartworm annually and avoid refilling the monthly parasiticide until the dog has tested negative. Dog owners are quite aware of the dangers of heartworm and are often diligent about preventing it. This is partly because of how expensive and potentially dangerous the treatment for heartworm can be, the informative and sometimes graphic informational leaflets to which the owners are exposed, and partially because it has become standard practice.

Treatment for intestinal worms is perceived as less serious than that of heartworm. With parasiticides for dogs and cats sold over the counter at pet stores, the consequences of infections are less dire, and owners are less apt even to consider regular testing outside of puppyhood and kittenhood.

Many owners are also under the impression that different geographical areas of the United States present a higher risk for all intestinal parasites. These thoughts are similar to that of tickborne illnesses4 and heartworm disease,5 despite data showing that these parasites can be found throughout the country. Often, these associations correlate with warmer weather, and people mistakenly believe that these types of parasitic infections are only a risk in hotter climates.5

In fact, many owners are not aware of how a pet may become infected with intestinal worms, such as roundworms, Trichuris trichiura (whipworms), and Echinococcus granulosus (tapeworms). These can be contracted via contaminated soil or contact with the feces of an infected animal, both of which are common in areas where there are multiple animals, such as parks, popular dog-walking trails, etc.

The public may also be unaware that these types of intestinal parasites are zoonotic diseases, and dogs and cats are the definitive hosts for the roundworm species that commonly cause infection in humans. If this information is more widely disseminated, pet owners may feel more compelled to do biannual testing, regardless of the presence or absence of symptoms in their pet, particularly because many owners come into regular contact with dog feces as a result of common etiquette surrounding canine hygiene in public.6

It may be prudent to engage in more grassroots education, either by making fecal centrifugation part of a biannual or at least, annual examination. In addition, pet owners should be provided with more information about the risks that tapeworms, roundworms, and whipworms pose to their pet, even after the animal reaches adulthood. Owners should also be encouraged to use a broad-spectrum parasiticide, such as milbemycin oxime (Interceptor), which protects against heartworm, as well as roundworms, whipworms, and tapeworms.

Moreover, it should be reiterated that these types of illnesses are zoonotic, can spread to humans relatively easily, and can result in more serious infestations in humans than in their animal counterparts.


  1. Trichuris vulpis. Companion Animal Parasite Council. Updated July 28, 2020. Accessed May 13, 2021.
  2. Ascarid. Companion Animal Parasite Council. Updated July 29, 2020. Accessed May 13, 2021.
  3. CDC. Transition of parasitic diseases. Reviewed February 17, 2021. Accessed May 13, 2021.
  4. Dogs, ticks and tick-borne parasites. Pet Health Network. Reviewed September 2, 2015. Accessed May 13, 2021.
  5. Incidence maps - American Heartworm Society. Published 2020. Accessed May 13, 2021.
  6. Who is uniquely susceptible to parasites transmitted by dogs and cats? Companion Animal Parasite Council. Published 2021. Accessed May 13, 2021.

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