Have you ever asked a client presenting with a pet with vomiting or diarrhea if the animal is on heartworm prevention? Is it relevant? It should be. Intestinal parasites commonly afflict our patients, and those on monthly heartworm prevention may be at lower risk than those without.

Asking clients about a pet’s exposure to other animals at dog parks, grooming, or daycare facilities for our canine friends and cats that go outside is paramount, but we need to take it further, evaluating the need for prevention with a One Health lens.

More than just prevention

Veterinarians have an ethical, if not legal, duty to diagnose, treat, and prevent zoonotic diseases.^1,2

When we take precautions to prevent intestinal parasites in our pets, we protect more than simply the animal itself. One Health considers not just the individual pet, but also the human-animal bond (HAB), the overall health of the environment, and the pet and the human populations as a whole.

Veterinarians must educate clients about the benefits of regular prevention and the risks of various parasites. They must also explain the transmission, life cycle, animal, human, and environmental interactions, and how these affect their pet, themselves, and others. Asking if a pet is on monthly heartworm preventatives is asking a lot more about a pet’s exposure risk and environment.

While monthly heartworm preventatives are appropriate, with climate change, shifting vector habitats, and their ever-increasing reach globally, even previously non-endemic heartworm areas are at risk of encroachment, putting more pets at risk. However, most heartworm preventatives also treat other parasites, some of which can also infect people. When veterinarians educate their clients about the further benefits these products provide, they not only protect pets, they also protect the pet’s family, further reinforcing the HAB.

Monthly zoonotic disease prevention

Regardless of our species of focus, veterinarians need to look beyond the individual pet. Heartworm preventatives stress the benefit of prevention. However, these products, to varying degrees, also protect against several intestinal parasites, some of which are zoonotic.

While mosquito vectors may be subject to changeable seasonal fluctuations worldwide, the expanding mosquito vector range usually warrants year-round heartworm prevention. Intestinal parasites are resilient in the environment, surviving for months or longer despite temperature variations and other factors, and cause infections year-round. Parasite protection is important for puppies and kittens, as well.³

Even if pets are on parasite preventatives, they should still get fecal evaluations regularly. This may be annually for pets with low exposure and more frequently if pets go to dog parks, daycare, or other high-exposure areas.⁴

Zoonotic potential

Hookworm or roundworm infections may be more prevalent in underdeveloped areas, but they happen everywhere. Feces from pets can easily contaminate the sand, soil, and plants, but so can defecation from wildlife species (e.g. foxes; they can all serve as primary hosts). Inquisitive pets can readily pick up an infective larva or egg.

People become exposed when skin penetration occurs, most commonly when walking barefoot on contaminated sand or soil. Other exposures occur by means such as accidental ingestion of parasitic infectious stages, due to improper hygiene, contaminated food, or pica. Children are especially susceptible because they are more prone to put objects in their mouths.

Accidentally ingesting the infectious stage of roundworms may cause visceral and ocular larval migrans. With hookworms, cutaneous larval migrans, exposure through skin penetration, is more common. However, hookworms can also cause damage to other organs, including the intestines.

Thankfully, dog and cat nematodes generally pass without incident in many people and cause no harm. However, serious complications due to parasite migration can occur. Humans act as dead-end hosts, whether or not illness occurs.

Disease prevalence

Parasitic infection prevalence and incident rates are vastly underreported in the U.S., in both the veterinary and human fields. There is some data, but it fails to truly elucidate the prevalence of the problem. More attention should be given to prevalence and data reporting.

In companion animals: The Companion Animal Parasite Council (CAPC) reports, as of February 28, 2023, 794,207 dogs were tested, and just shy of two percent were positive for roundworms (Figure 1).⁵ For cats, almost five percent of those tested were positive.

For 2023 hookworm cases in dogs, 2.33 percent (Figure 2),⁶ have tested positive. In comparison, for cats, only 0.62 percent of the population tested to date showed evidence of active hookworm infection. Still, these numbers highly underestimate the true incidence of disease. All practices that perform in-house testing do not report those cases, and not all clinical laboratories report. Thus, CAPC data clearly lowballs the U.S.’ total burden of disease.

In humans: According to the Centers for Disease Control and Prevention (CDC), five percent of the American population becomes infected with Toxacara species annually. However, the prevalence may be as high as 40 percent in other parts of the world. Hookworm prevalence is less well elucidated in people. Estimates for children in Brazil are as high as 15 percent, while for people over 20, the prevalence is less than one percent. This organism, like roundworms, poses a significant threat to human health and warrants a One Health approach.^7,8

Knowledge gaps

Complacency is a common problem with parasite control. While on an initial pet visit, a discussion may be initiated about heartworm prevention, and a brief education session on the zoonotic risks of some intestinal parasites may be given. Such discussions may be less frequent on subsequent visits.

Owner compliance can also be a problem. Owners may not want to administer products to their pets, or pets may resist treatment. Pet parents may also not truly understand the risks and overall safety of most current products. They may have simply never had a veterinarian take the time to review the products and the rationale for their use. Owners may opt out of monthly prevention if they do not understand the zoonotic risks involved. As proponents of zoonotic disease prevention, a veterinarian’s duty is to inform owners properly.

Using roundworm and hookworm infections as examples; despite all we know, further research is still needed. Multiple epidemiological factors are still poorly expounded. Further, despite parasite infections being a ubiquitous zoonotic problem, an interdisciplinary research approach combining environmental, veterinary, and medical disciplines in various research efforts is still lacking. More information about the incidence and true seroprevalence of the disease in people and animals globally and locally is required.^9,10

Conclusions

Ideally, our efforts need to aim to reduce infection. Veterinary professionals should be at the forefront by providing client education and deworming our patients preventatively and in clinical disease. Veterinarians must educate the individual pet parent, their community, and society. A One Health approach must evaluate wildlife, companion animals, the environment’s role in the transmission cycle, and the risks to all potentially affected species.⁹

Holland, C.V.⁹ states more knowledge about adult dogs’ role as potential sources of infections is needed. At the same time, research clearly understands the role kittens and puppies play as sources of infection. Veterinarians must ensure owners understand this risk and how to thwart it.

Human physicians must also ensure they ask about environmental exposure risks when facing patients with possible infectious diseases. When confronted with infected human patients, doctors should ask questions about pet ownership, visits to dog parks, petting zoos, and other arenas where exposure to zoonotic diseases could lead to clinical disease. Up-to-date zoonotic disease continuing education for physicians is warranted to ensure pets presenting with ailments from diarrhea to tick-borne-like illnesses are appropriately addressed. Improving One Health cooperative efforts can limit suffering and debilitation in all species.

Cooperative efforts among physicians, veterinarians, and other stakeholders are essential to diagnose infectious disease cases more rapidly and accurately. The ability to more accurately and consistently diagnose infection in various species would improve clinical outcomes. Currently, veterinarians rely primarily on fecal flotations for the diagnosis of parasite infections.

However, many infections may be missed because they are in the pre-patent period, are not actively shedding parasites, or because only a small aliquot of an individual’s feces is sampled. Further research on improved diagnostic testing may help elucidate the true incidence of parasite infections and allow therapeutic interventions to be delivered faster and more effectively.¹⁰

Erica Tramuta-Drobnis, VMD, MPH, CPH, is the CEO and Founder of ELTD One Health Consulting LLC. Dr. Tramuta-Drobnis works as a public health professional, emergency veterinarian, freelance writer, researcher, and consultant. She is a member of the Evidence-Based Veterinary Medical Association (EBVMA), with different members writing this column. While all articles are reviewed for content, the opinions and conclusions of the author(s) do not necessarily reflect the views of the EBVMA or Veterinary Practice News. For information about the association or to join, visit https://www.ebvma.org.

References

1. Traub RJ, Irwin P, Dantas-Torres F, et al. Toward the formation of a Companion Animal Parasite Council for the Tropics (CAPCT). Parasit Vectors. 2015;8:271. doi:10.1186/s13071-015-0884-4 https://parasitesandvectors.biomedcentral.com/articles/10.1186/s13071-015-0884-4
2. Marsh AE, Babcock S. Legal implications of zoonotic disease transmission for veterinary practices. Vet Clin North Am Small Anim Pract. 2015;45(2):393-408, vii. doi:10.1016/j.cvsm.2014.11.008 https://pubmed.ncbi.nlm.nih.gov/25555561/
3. The Companion Animal Parasite Council (CAPC). Pets & Parasites: The Pet Owner’s Parasite Resource: Controlling Internal and External Parasites in U.S. Dogs and Cats. Pets and Parasites (CAPC). Accessed February 28, 2023. https://www.petsandparasites.org/resources/capc-guidelines
4. Little S. Parks, Pets, & Parasites: Controlling Canine Intestinal Helminths. Clinician’s Brief. 2020; January 2020. Accessed March 1, 2023. https://www.cliniciansbrief.com/article/parks-pets-parasites-controlling-canine-intestinal-helminths
5. CAPC. Parasite Prevalence Maps: Intestinal Parasites, roundworms, dogs. Pets and Parasites (CAPC). Published March 1, 2023. Accessed March 1, 2023. https://www.petsandparasites.org/parasite-prevalence-maps/#/2023/all-year/roundworm/dog/united-states
6. CAPC. Parasite Prevalence Maps: Intestinal Parasites, hookworms, dogs. Pets and Parasites (CAPC). Published February 28, 2023. Accessed February 28, 2023. https://www.petsandparasites.org/parasite-prevalence-maps/#/2023/all-year/hookworm/dog/united-states
7. Centers for Disease Control & Prevention (CDC). Toxocariasis – Epidemiology & Risk Factors. Centers for Disease Control and Prevention. Published September 3, 2019. Accessed February 28, 2023. https://www.cdc.gov/parasites/toxocariasis/epi.html
8. Centers for Disease Control & Prevention (CDC). Zoonotic Hookworm. Centers for Disease Control and Prevention. Published January 15, 2021. Accessed February 28, 2023. https://www.cdc.gov/parasites/zoonotichookworm/index.html
9. Holland CV. Knowledge gaps in the epidemiology of Toxocara: the enigma remains. Parasitology. 2017;144(1):81-94. doi:10.1017/S0031182015001407 https://pubmed.ncbi.nlm.nih.gov/26670118/
10. Traub RJ, Zendejas-Heredia PA, Massetti L, Colella V. Zoonotic hookworms of dogs and cats – lessons from the past to inform current knowledge and future directions of research. International Journal for Parasitology. 2021;51(13):1233-1241. doi:10.1016/j.ijpara.2021.10.005 https://pubmed.ncbi.nlm.nih.gov/34748782/