Updates on Gastrointestinal Parasites with Zoonotic Potential

Over half of U.S. and Canadian households are home to a dog or cat. Pet ownership confers many benefits to humans, but, as with almost everything in life, it also can come with risks –– including the potential for zoonotic disease.

Zoonosis can be a complicated and confusing topic for pet owners and veterinary professionals alike, thanks in part to the ever-evolving nature of infectious diseases. Just when you think you have a handle on the situation in your clinic, a new parasite emerges or becomes resistant to antimicrobial drugs that used to work.

We recently spoke with Antech’s Global Director of Veterinary Clinical Education, Michelle. Evason, BSc, DVM, DACVIM (SAIM), MRCVS, on the topic of gastrointestinal parasites with zoonotic potential — specifically Giardia duodenalis, Ancylostoma caninum (hookworms), Echinococcus multilocularis (fox tapeworms), and Baylisascaris procyonis (raccoon roundworms) — to gain a better understanding of the current state of affairs and how KeyScreen™ GI Parasite PCR can support veterinary teams in their day to-day work of keeping pets and their people safe.

What are some common misconceptions about zoonosis among pet owners?

I think zoonosis can be confusing for many people –– including the very definition of the word. Zoonosis refers to any infectious disease that’s transmitted directly from an animal (such as a dog or cat) to a human, and vice versa. I often hear people referring to vector- borne diseases like Lyme disease as being zoonotic, but dogs get Lyme the same way we do (from tick bites), so it’s not actually zoonotic.

Awareness of infectious disease risk is another point of confusion, as pet owners often don’t understand where the risks are coming from (e.g., dog parks, regions we didn’t find many of these bugs in the past); who’s most at risk (YOPI: young, old, pregnant, immunocompromised people); or what an infected pet can look like (i.e., they may not have any clinical signs of infection, like diarrhea).

Pet owners may also not understand how ‘tough’ and environmentally resistant GI parasites are. For example, many can survive for months in the environment — even in harsh temperatures like Canadian winters.

---

FREE PET OWNER HANDOUT
Zoonotic Diseases & Kids: 5 Risks Dogs & Cats Pose to Children
Use this handout to help families understand and minimize the risks of zoonotic disease, including roundworm, hookworm, Giardia, leptospirosis, and ringworm. 

---

How concerned do we need to be about Giardia zoonosis? 

Until recently — “recently” being the launch of KeyScreen, which can detect not only Giardia, but also whether it’s an assemblage, or strain, that can infect humans (assemblage A or B) — we didn’t really have a good handle on the risk of Giardia passing from pets to humans. But thanks to KeyScreen tests submitted by veterinary teams as part of routine fecal testing in pets, we now have an immense amount of data at our disposal to investigate and inform on these risks, making it easier to help answer this question regarding the level of zoonotic concern.

For example, we now know that less than 4% of dogs with detected Giardia have Giardia
assemblages A or B. Thus, less than 4% of dogs with Giardia pose a zoonotic risk_.¹ However, we also know that the risks are a little different when it comes to cats. Looking at KeyScreen test data from Canada and the United States, as well as from Asia and Brazil, we found that while cats are overall less likely to have Giardia than dogs, when Giardia is detected, it’s more likely to be an assemblage with zoonotic potential (15 – 25%).¹ This is one of those things that’s important for pet owners to be aware of, because unlike dogs, many cats don’t usually stay on the floor. They’re on our countertops and keyboards and in our laps.

Demonstrating the importance of risk reduction through hygiene practices is an important
conversation to have with pet owners, especially if they’re in a higher risk group (YOPI).

Should we be treating pets infected with Giardia who don’t have any clinical signs?

If Giardia is detected in a pet who doesn’t have clinical signs, the answer to this question these days is almost always no — we don’t typically advise treating that dog or cat. This is a pretty recent change in veterinary thinking, where finding a ‘bug’ doesn’t automatically require specific antimicrobial treatment.

Some background on this change and increased attention on antimicrobial stewardship is that the World Health Organization has ranked antimicrobial resistance (which includes antibiotics and anthelmintics) as one of the top global health threats. And unfortunately, the misuse and overuse of antimicrobials in humans, animals, and plants are recognized as some of the main drivers of drug resistance, which means we all need to play our part in mindful antimicrobial use and not use drugs when they aren’t indicated.

One of the things I’m most proud of from the past year at Antech is how we’re using veterinary test data to create clinical decision-making algorithms [including the KeyScreen Giardia algorithm] to help support veterinarians through difficult and nuanced situations, like Giardia detection and when and if treatment is appropriate.

For example, while we wouldn’t typically recommend treatment for a Giardia-detected dog who doesn’t have clinical signs, that conversation might change if the KeyScreen results indicate that the Giardia is of the zoonotic potential (A or B) assemblage and the pet lives with an immunocompromised individual or with someone who’s young, older, or pregnant. In a case like this, and in communication with the pet owner, treatment may be reasonable and appropriate.

To use another example of how this information helps us, imagine we have a pet with diarrhea in whom Giardia is detected. Following treatment, the signs (diarrhea) resolve, but the positive Giardia test result persists. Until recently, we would’ve kept treating that pet. But now, we’re checking ourselves in the name of antimicrobial stewardship. We longer have the mentality that we have to kill every bug we find, and we’re actively using diagnostic stewardship to choose the correct test if we decide to re-test following therapy.

And if we see a patient who continues to have clinical signs following treatment, we can use decision-making algorithms to explore the possibility that something else is going on with that pet and get guidance regarding what to do next.

These are some real shifts in how we think about parasites, and I’m grateful we have these algorithms, as well as the collaboration of infectious disease experts, to support these changes.

What’s the latest on drug resistance in hookworms? Is it something we need to worry about outside of Florida’s racing greyhound population?

Hookworm is sort of like the poster child for how antimicrobial resistance can get going, and it’s drawn a lot of attention to the rising problem of parasite resistance. Hookworm drug resistance was first found in Florida’s racing greyhound population around six or seven years ago. Unfortunately, this discovery came after the greyhounds started being adopted and re-homed by people living all over the United States.

KeyScreen can detect not only hookworms, but also whether these worms are resistant to some of the most common drugs used to kill them (benzimidazoles, like fenbendazole and febantel). And thanks to test data submitted from veterinary teams, we now know that hookworm resistance isn’t just in Florida.² In fact, it’s moved all the way across the United States. We’ve even found cases in Canada, demonstrating the rapid spread of parasite resistance in a very short period. We also know from looking at the data that it’s no longer just a greyhound problem, as it’s been found in more than 70 different dog breeds.²

Before KeyScreen, hookworm resistance could only be diagnosed via a fecal egg count reduction test or by sending samples to an academic laboratory. KeyScreen provides a simple, affordable, and fast result so veterinarians can start patients on an effective treatment regime and monitoring program as soon as possible.

Is Echinococcus multilocularis a problem in North America?

Though this parasite has traditionally been a problem in Europe, we now know that E. multilocularis is emerging in Canada and the United States. It’s always a fine line to walk with infections like this, because while infection is rare, the consequences of this parasite in human and canine health are high (and rather nasty).  

It’s really important for veterinarians to be aware of and raise awareness about this parasite to pet owners because of the disease it can cause in both people and dogs –– alveolar echinococcosis. This disease is characterized by cyst-like masses that can act similar to tumors. The masses are usually found in the liver, though it can be present in the lungs, brain, and other organs. Alveolar echinococcosis is really tough to treat and can take months to years to emerge. It’s not a disease I would ever want to get 

KeyScreen data has been critical to tracking its spread to new regions, especially states in the U.S. where it’s never been found before, as E. multilocularis isn’t detected by fecal and ova parasite exams or through fecal antigen testing.³  

Is the same true for Baylisascaris procyonis?

Yes. In North America, almost every raccoon is infected with B. procyonis, or raccoon roundworm, and this is a parasite that can also infect dogs and humans. If you have raccoons in your area, raccoon roundworms are in your environment. And if a dog is shedding this parasite, their humans have a much greater risk of exposure.

Raccoon roundworm rarely causes disease in people. But when it does it can cause severe neurological disease and damage, so it’s extremely important to track and be aware of. Dogs aren’t usually sick when they have this parasite, so when we find it through fecal screening, we can communicate the risk to pet-owners and encourage them to speak with their human healthcare provider regarding whether prophylactic treatment may be appropriate.

This is another parasite that can be a challenge to identify with fecal ova and parasite testing, further underscoring the benefit of KeyScreen in helping veterinary teams with zoonotic risk conversations.

If one thing is clear from our interview with Dr. Evason, it’s that GI parasites and their potential to cause zoonotic disease demands our careful attention. As these parasites continue to evolve and spread, we must continue to innovate and implement methods of detection like KeyScreen. We must also engage in proactive conversations on zoonotic risks that help clients see the connection between their pet’s health and wellness and their own to further enhance this important bond and help make a better world for pets –– and their people. 

Experience diagnostically superior GI parasite screening with KeyScreen.⁴   

• Screens for 20 intestinal parasites  
• Detects more infections when compared to O&P  
• Detects Giardia with zoonotic potential 
• Detects benzimidazole resistance in hookworms  

This is evolutionary parasite detection. 

---

References