Pet parasite risks are evolving. Is your practice prepared?

When I moved from southeastern Pennsylvania to central Kentucky a few years ago, I noticed something that stuck with me: nobody talked about Lyme disease.

In Pennsylvania, it came up often, especially in equine practice, where clients frequently requested testing for vague or hard-to-define concerns ranging from subtle lameness to behavioral changes that didn’t quite add up. Interpretation in horses was (and still is) less straightforward than in dogs or people, but the disease was firmly part of the conversation.

In Kentucky, it rarely came up. At the time, that made sense. The perceived risk was lower, and Lyme disease simply wasn’t top of mind for many veterinary teams or their clients.

According to the 2026 Companion Animal Parasite Council (CAPC) Pet Parasite Forecast, that perception is beginning to shift. Lyme disease, heartworm, ehrlichiosis, and anaplasmosis are expanding into regions that have historically been low risk, raising a new set of questions for veterinary teams. We know the map is changing, but are clinical protocols, client conversations, and everyday assumptions keeping pace with it?

Parasite risk expansion: An overview

Each year, CAPC releases its Pet Parasite Forecast. These predictive models, built on more than a decade of surveillance data and diagnostic test results, have historically exceeded 94% accuracy, making them a reliable tool for anticipating what veterinary teams are likely to see in practice. These forecasts incorporate multiple variables, including diagnostic trends, environmental conditions, and human population factors.

For 2026, the forecast projects continued geographic expansion of four key vector-borne diseases: Lyme disease, heartworm, ehrlichiosis, and anaplasmosis.

That expansion is already showing up in reported data. Comparing the 2022 and 2025 American Heartworm Society (AHS) incidence maps tells a clear story: high-incidence areas are pushing north along the Mississippi River corridor and the Atlantic coast, and new pockets of elevated risk are showing in places like the Mountain West, Northern California, and the Northern Plains.

Convergence of factors

So, what’s driving the shift? The answer isn’t a single factor, but a convergence of many. Warmer temperatures and shifting climate patterns are allowing ticks and mosquitoes to survive and thrive in areas where they couldn’t before.

Jason Stull, DVM, MPVM, PhD, DACVPM, co-chair of the upcoming AAHA One Health Guidelines: Emerging Concerns in Canine and Feline Parasitology task force (launching this fall), noted that geographic spread is part of what’s driving the changing picture.

“The emergence of parasites is a key area driving infectious disease risk right now. This includes parasites expanding from one area to another and becoming established.  This is clearly shown with the steady movement of Lyme disease from the northeast United States westward, the rapid increase of anaplasmosis in dogs along the East Coast, and tick species moving into new regions (such as the Gulf Coast tick, which is moving north into the northeastern U.S.),” he said.

And when animals (and people) move around, they bring parasites with them. Andy Moorhead, DVM, MS, PhD, DACVM (Parasitology), Symposium Program Chair with the American Heartworm Society, pointed to large-scale weather events as one piece of the puzzle, noting that “massive weather events that cause displacement of animals” can accelerate the spread of parasites from higher-prevalence areas to lower-prevalence areas. Even outside of acute events, routine relocation can have similar effects.

“More people just need to be aware that when you move animals from one place to another, you could be moving their diseases—the same way with people,” Moorhead said.

A 2017 study examining dog importation into Colorado found that heartworm prevalence increased by 67.5% between 2013 and 2017, during a period when more than 114,000 dogs were transported into the state, many from regions with higher heartworm incidence. The data suggest that movement of dogs from endemic areas may contribute to increasing local transmission risk, even in regions historically considered low prevalence.

Kathryn Duncan, DVM, PhD (Parasitology), also pointed to growing attention around specific parasite concerns, including invasive species like the longhorned tick, emerging zoonotic parasites such as Echinococcus, and resistant parasite populations. “These risks aren’t necessarily new,” she noted, “but they’re being recognized more as diagnostics improve and awareness grows.”

Underrecognized risks

Both the CAPC and AHS maps show irrefutable data about parasite expansion, but, as Duncan noted, whether practices in areas of new expansion are prepared for what’s coming is another question.

Part of the gap is simply awareness. Duncan emphasized that many of the most meaningful shifts are happening at the edges of known parasite distributions, areas where awareness tends to lag behind reality.

“Geographic shifts are often underrecognized where parasites are just starting to emerge,” she said. “These changes are typically tied to habitat shifts, host movement, and wildlife population changes.”

“If you are in an area where a disease has not historically been, it’s not necessarily going to be on your radar how to deal with it,” Moorhead said. “That’s not due to a lack of diligence — if you aren’t aware of something and don’t think about it, you’re not going to necessarily be able to test for it.”

Stull pointed to a different blind spot: resistant strains.

“Currently, I think there is limited appreciation for parasiticide resistance,” he said. “Although not yet widespread across the US or Canada, this poses a huge risk in the future.”

In other words, even practices that are testing and treating may be operating on assumptions about how well those treatments work. Resistant hookworms in dogs have been documented for years and are not a new development. Heartworm resistance has also been identified. Together, these patterns suggest that while resistance may not yet be widespread, it is already present and should be factored into prevention and treatment strategies.

Testing and prevention gaps

Veterinary professionals may be aware that parasite risk is changing, but awareness alone doesn’t update day-to-day protocols.

Testing is one of the first areas where gaps may show up. “As diseases move into new areas, people may not necessarily be aware that they need to test for them,” Moorhead said.

That challenge extends to test selection. Duncan noted that in areas where parasite risk is shifting, more comprehensive diagnostics may be needed, and relying on limited or less sensitive methods can lead to missed diagnosis.

“If we focus only on the most common parasites, we risk overlooking others that may be emerging,” she said. “Techniques like centrifugal fecal flotation or incorporating coproantigen or PCR testing can improve detection.”

Even when awareness is there, putting testing into practice isn’t always straightforward. It depends on getting the client in, getting the right sample, and balancing that against cost and other priorities.

That reality makes consistency difficult, especially in areas where clients may not yet see parasite risk as a priority.

Prevention presents similar challenges. Recommendations need to be realistic for the practice and the client. “The right prevention is the one that the client will consistently give,” Moorhead says. “It has to fit the culture of your practice.”

Duncan added that prevention strategies may also need to expand beyond pharmaceuticals alone, and that some of the most effective tools are also the most basic.

“We’ve become very reliant on dewormers,” Duncan said, “but simple measures like prompt fecal removal, good hygiene, and preventing behaviors like coprophagia can significantly reduce risk.”

For ectoparasites, she added, hands-on exams remain one of the most effective tools, not only for detection, but also for demonstrating proper removal techniques to clients.

Client and clinic communication

Changing protocols means changing communication.

Moorhead described client communication as a series of steps. “You have to get over three hurdles: awareness, belief in risk, and behavior,” he said.

In areas where parasite risk is increasing but awareness is still low, that first step of helping clients recognize the risk can’t be skipped.

Stull emphasized that point. “In locations where there is emerging or increasing disease risk, but client awareness is low, veterinary professionals will need to take additional steps to ensure clients understand why specific preventive or testing measures are being recommended,” he said.

He noted that tools like CAPC maps can help make that risk visible, especially when they are used throughout the client experience, from the waiting room to the exam room. “Attempting to move clients immediately into more in-depth conversations or decisions without first allowing the client to acknowledge the disease risk itself is unlikely to be as effective,” he said.

Duncan echoed the importance of grounding those conversations in local data.

“Using resources like CAPC and AHS to show what’s happening in your area helps make the risk real,” she said. “Finding a parasite or vector-borne pathogen is often the most effective starting point for a prevention conversation.”

She also emphasized the importance of consistency, particularly when zoonotic parasites are involved, noting that clear, take-home guidance for clients can help reinforce recommendations beyond the exam room.

Consistency matters just as much internally. “From front desk to technician to veterinarian—all have to be on the same page,” Moorhead said.

That includes not just what is recommended, but how it’s explained. “Showing the client how to give the medication, telling them how you’re going to remind them, [explaining] that this is so important for the health of the pet,” he said.

Clear, simple communication, repeated consistently across the team, can make the difference between a recommendation that’s heard and one that’s followed.

Looking ahead

“We are not going to see a lessening in parasite prevalence,” Moorhead said.

As long as there are gaps in prevention, transmission will continue, he continued: “If there’s unprotected pets, there’s the ability for transmission.”

At the same time, resistance is adding another layer of complexity. “We do have resistant hookworm out there and I think we are only going to see a spread of that,” he said.

That combination of expanding geographic risk and evolving parasite behavior means veterinary teams may need to adapt more quickly than they have in the past.

Looking ahead, Duncan also expects parasite risk to continue rising as environmental and population factors evolve.

“We’re going to keep seeing changes driven by shifting animal distributions, climate factors, and travel,” she said. “Diagnostics and research will continue to improve, but collaboration between clinicians, researchers, and industry will be critical.”

She also noted that future control strategies may require revisiting older approaches alongside newer tools. “We’ll likely need to reintegrate basic prevention measures—like fecal cleanup and environmental management—while using parasiticides more intentionally.”

Taken together, the message is simple: the map is changing, and practice has to change with it. Communication and consistency in both messaging and action is key to keeping veterinary patients—and their people—safe as we navigate a changing parasite landscape.

Photo credit: Bogdan Kurylo/iStock via Getty Images Plus

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