Expanding Risk: Unpacking the 2026 Pet Parasite Forecast

The Companion Animal Parasite Council (CAPC) recently released its 2026 Pet Parasite Forecast, just as it has done for the past 14 years. This forecast projects continued geographic expansion of canine Lyme, anaplasmosis, ehrlichiosis, and heartworm disease. Because of this expansion, including into areas that were formerly considered at low or moderate risk, veterinarians are advised to endorse the use of year-round preventatives, adjust vaccination strategies according to local risk, and encourage annual testing.

Editor’s Note: This is an excerpt from Research Wrapped, a free monthly newsletter that collects the latest scientific research relevant to small animal veterinarians and pulls out practical takeaways. To be the first to receive this newsletter each month, subscribe here.

This month, we spoke with Dr. Kathryn Reif, MSPH, PhD, who is on the board of directors of the CAPC, the lead author of the 2026 forecast, and an associate professor at the College of Veterinary Medicine at Auburn University.

Q: Can you explain the CAPC’s process for making annual forecasts?

CAPC’s annual forecasts for Lyme disease, anaplasmosis, ehrlichiosis, and heartworm are generated from a large, continually updated surveillance framework that integrates veterinary diagnostic test results with historical disease patterns, environmental conditions, ecological factors, socio-demographic variables, and information on relevant tick and mosquito vectors. Using Bayesian spatio-temporal modeling, these inputs are used to estimate the percentage of dogs likely to test positive in a given geographic area over the forecast year. Because CAPC incorporates millions of test results from across the United States each year, the forecasts provide a highly informed view of parasite and vector-borne disease risk at national, regional, and local scales. Historically, the models have shown greater than 94% accuracy, making the maps a practical tool for helping veterinarians anticipate disease risk, interpret local testing trends, and communicate the importance of routine testing and year-round parasite prevention with clients.

Q: Considering the past predictions have been more than 94% accurate at estimating the true prevalence of these 4 diseases across the United States, what are the biggest concerns for 2026?

Lyme disease: The biggest concern for 2026 is continued expansion of Lyme disease risk beyond the traditional Northeast and Upper Midwest hotspots. The Lyme disease forecast highlights increasing concern across parts of the Midwest and Appalachia, including Indiana, Illinois, Michigan, Ohio, Kentucky, West Virginia, northern Tennessee, and western/northwestern North Carolina, meaning veterinarians in historically lower-risk areas should reassess tick prevention and Lyme vaccination discussions.

Anaplasmosis: Anaplasmosis risk continues to track with expanding blacklegged tick populations, especially in the Northeast, Upper Midwest, parts of Appalachia, and increasingly along the West Coast. The anaplasmosis forecast also notes that higher risk in the Southwest most commonly reflects Anaplasma platys transmission by brown dog ticks, which makes local tick ecology and regional interpretation of test results especially important. 

Ehrlichiosis: Ehrlichiosis remains a major concern across the Southeast, South-Central, Southwest, and Atlantic coastal states, with additional concern in western states such as Arizona, New Mexico, Colorado, Utah, and Wyoming. The ehrlichiosis forecast also points to northward expansion of lone star tick–associated risk, meaning veterinarians in parts of the upper Midwest and New England should be increasingly alert to ehrlichiosis even if it has not historically been top-of-mind.

Heartworm disease: Heartworm risk remains highest in the Southeast but continues to expand northward along the Mississippi River corridor and Atlantic Coast, placing much of the central and eastern U.S. at increasing risk. The heartworm forecast also highlights persistent pockets of elevated risk in parts of the West and Northern California, reinforcing that heartworm is not only a “Southern disease” and that dog movement, mosquito expansion, climate, and inconsistent prevention all contribute to ongoing spread.

Big takeaway messages: The 2026 forecasts reinforce that vector-borne disease risk is dynamic, local, and changing. “Low risk” does not mean “no risk,” especially for pets that travel or are relocated. Veterinary teams should use CAPC maps as a client communication tool to support annual testing, consistent year-round parasite prevention, and regionally appropriate tick and mosquito control recommendations. Positive vector-borne disease tests should also be viewed as evidence that a dog has had meaningful vector exposure, making them valuable prompts to reassess prevention plans.

Editor’s Note: This article is an excerpt from the Research Wrapped monthly newsletter. Subscribe here for free.

Q: What are the biggest differences in findings compared to the forecasts of 2025?

Lyme disease: Compared with 2025, the 2026 forecast places more emphasis on specific expansion zones beyond the traditional Northeast and Upper Midwest, especially Ohio, Kentucky, West Virginia, northern Tennessee, and western/northwestern North Carolina. The 2026 forecast also highlights continued westward pressure into North Dakota, eastern Montana, northern South Dakota, and Iowa, reinforcing that Lyme risk is not only expanding southward but also filling in and extending westward from established Upper Midwest foci.

Anaplasmosis: The overall pattern is similar to 2025, but the 2026 forecast more clearly links increasing anaplasmosis risk with expanding blacklegged tick populations and rising Lyme disease risk in the same regions. It also gives stronger attention to the Southwest, where higher anaplasmosis risk more commonly reflects Anaplasma platys transmission by brown dog ticks, making local tick ecology especially important for interpretation.

Ehrlichiosis: The 2025 forecast noted increasing ehrlichiosis risk in western states such as Colorado, Utah, and Wyoming; the 2026 forecast broadens that concern to include Arizona and New Mexico as well. The 2026 forecast also more explicitly separates likely lone star tick–associated ehrlichiosis patterns in the East from brown dog tick–associated E. canis risk in the West and Southwest.

Heartworm disease: The 2026 heartworm forecast is broadly consistent with 2025: highest risk remains in the Southeast with continued expansion northward along the Mississippi River corridor and Atlantic Coast. The biggest difference is the stronger emphasis that heartworm risk is becoming entrenched or unexpectedly elevated in areas not always viewed as traditionally endemic, including parts of the central U.S., western states, and Northern California.

Big takeaway messages: The 2026 forecast reinforces that the risk for these vector-borne diseases is not retreating, but instead continues to expand, intensify, or become more geographically complex. For veterinary teams, the most important shift is that “regional risk” can no longer be defined only by traditional endemic maps. Tick- and mosquito-borne disease prevention should be year-round, travel history matters, and positive test results for dogs should be treated as evidence of meaningful vector exposure in that community. The CAPC 2026 forecast also strengthens the One Health message: dogs are not just patients; they are sentinels that help identify changing vector-borne disease risk for people as well.

Q: What are the primary takeaways for private practice veterinarians?

1. Annual testing needs to remain a standard recommendation. The CAPC forecasts reinforce that exposure risk is changing, and annual testing is one of the best ways to identify infected or exposed dogs before infection or disease is missed. Testing also helps practices recognize what is happening locally, not just what is expected based on older regional assumptions.
2. Year-round tick and mosquito prevention should be routine, not seasonal. Because tick and mosquito activity is increasingly variable across regions and seasons, prevention recommendations should not be limited to the “traditional” parasite season. Consistent use of effective tick and heartworm prevention is central to reducing exposure to Lyme disease, anaplasmosis, ehrlichiosis, and heartworm.
3. Pets are sentinels for broader public health risk. When dogs test positive for vector-borne pathogens, that tells us infected ticks or mosquitoes are active in the environment shared by pets and people. Canine test results can therefore help veterinary teams increase awareness of local One Health risk, reinforce the importance of consistent parasite prevention for pets, and create opportunities to guide clients on practical steps they can take to reduce tick and mosquito exposure for themselves and their families.
4. Disease risk ranges are expanding and becoming less predictable. The 2026 forecasts show that Lyme disease, anaplasmosis, ehrlichiosis, and heartworm risk are no longer confined to historically recognized endemic areas. Veterinarians should use current forecast maps and local diagnostic trends rather than relying only on older geographic risk assumptions.
5. Pet movement matters. Dogs that travel, relocate, are adopted from other regions, or move through shelters and rescue networks may be exposed to parasites and pathogens outside their home area. Movement can also contribute to the spread of infected pets, vectors, or vector-borne disease risk into new communities, making travel history and origin history important parts of preventive care conversations.

Big-picture message: For private practice, the practical takeaway is simple: test annually, prevent consistently, ask about travel and relocation, and use CAPC maps to make parasite risk visible to clients. These forecasts give veterinary teams a concrete way to move the conversation from “Is this a problem here?” to “Here is what the data suggest we should be prepared for in our community.”

Editor’s Note: This article is an excerpt from the Research Wrapped monthly newsletter. Subscribe here for free.

Q: Is there anything you would like our readers to know that has not been mentioned?

1. Veterinarians are on the front line of emerging risk. Private practice veterinarians and veterinary technicians are often the first people to recognize when something new is happening. A dog with an unexpected positive test result, an unusual-looking tick, a different pattern of disease, or a parasite problem that seems out of place may be an early clue that local risk is shifting. That makes veterinary teams an essential part of our broader surveillance network. The cases you see in practice do not just matter for that individual patient; they can help identify emerging risks for other pets, people, livestock, and wildlife in the same community.
2. New World screwworm is a reminder that ectoparasite control matters beyond fleas and ticks. New World screwworm is an important emerging threat to keep on the radar because it can affect pets, livestock, wildlife, and, rarely, people. These flies are attracted to wounds and body openings, and infestation can occur in wounds as small as an open tick bite. Effective ectoparasite control, routine tick checks, prompt wound care, and close monitoring of skin lesions are all practical ways to reduce opportunities for infestation and improve the chances of early detection. This is another example of why parasite prevention should be viewed as part of overall animal health preparedness, not just routine monthly medication.
3. Use prevention conversations as a relationship-building tool. Parasite prevention is not just a product recommendation; it is a recurring opportunity to educate clients and strengthen the veterinarian-client-patient relationship. CAPC maps and annual testing results give teams a concrete way to show clients that parasite risk is real, local, and changing. When clients understand the “why” behind testing and prevention, they are more likely to follow through consistently.
4. Low risk is not no risk. Forecast maps help us understand relative risk, but individual pets may have very different exposure depending on travel, outdoor activity, wildlife contact, adoption or relocation history, and prevention compliance. That is why annual testing, year-round prevention, and individualized risk assessment remain important—even in areas that are not considered high-risk.
5. Veterinary data are powerful. The diagnostic work done in private practice has value beyond the individual patient. Each heartworm or vector-borne disease test helps build a clearer picture of where parasites and pathogens are being detected and how those patterns are changing over time. When veterinary teams test regularly and report those results, they contribute to a broader surveillance system that supports better risk prediction, stronger prevention recommendations, and improved protection for pets and the people who share their environments.
6. Parasite prevention protects the human-animal bond. Consistent parasite prevention helps protect not only pet health, but also the everyday closeness people enjoy with their animals. When pets are protected from fleas, ticks, mosquitoes, and vector-borne disease threats, families can more confidently include them in the activities that strengthen the human-animal bond, from walks and travel to outdoor adventures and quiet time at home. Effective prevention helps keep pets comfortable, reduces the chance of parasites entering shared spaces, and supports the peace of mind that allows people and pets to fully enjoy life together.

Read the Full Forecast

Companion Animal Parasite Council 2026 Annual Pet Parasite Forecast

Reif K. 2026 annual pet parasite forecasts. Companion Animal Parasite Council | Published March 23, 2026 | capcvet.org/articles/2026-annual-pet-parasite-forecasts/