The Maps Have Changed. Has Your Prevention Protocol?

Every year, the Companion Animal Parasite Council releases its annual forecasts for the four vector-borne diseases that matter most to companion animal practice in the United States: Lyme disease, heartworm, ehrlichiosis, and anaplasmosis. Every year, the maps shift a little. The ranges expand. The risk zones creep into counties that were not on the radar twelve months ago.

And every year, somewhere across the country, a veterinarian has a conversation with a client about a disease that "does not exist here" — right before a positive test result proves otherwise.

The 2026 forecasts are out. The picture they paint is not alarming in the way that headlines want disease stories to be alarming. It is more specific than that. More granular. More actionable. And for veterinary professionals who are paying attention, it is a direct call to look at their prevention protocols, their client education, and their testing recommendations before the cases arrive — not after.

Here is what the data says.

The Ground Is Shifting — And Has Been for Years

Before getting into the individual diseases, it helps to understand what is actually driving the changes in these maps year over year. Because it is not one thing. It is everything at once.

Climate change is extending the seasonal activity windows of ticks and mosquitoes into months that historically would have been safe. Warming temperatures are pushing vector habitats northward and into higher elevations. Land use changes — reforestation, suburban development pushing into wooded and peri-urban areas, agricultural landscape shifts — are creating new contact points between pets, people, and the vectors carrying pathogens. Wildlife population dynamics, particularly deer densities, are sustaining tick reproduction at scale. And the movement of dogs — rescued, relocated, transported across state lines with the best intentions — is introducing infected animals into regions where local mosquito and tick populations are fully capable of picking up and transmitting what those dogs are carrying.

The result is a disease landscape that does not respect the old maps. And a profession that was trained on regional risk assumptions that are quietly becoming outdated.

The CAPC forecasts are built on over 10 million diagnostic test results per vector-borne disease reported annually from across the United States. They have historically exceeded 94 percent accuracy in estimating true prevalence. These are not projections built on modeling alone. They are built on what dogs are actually testing positive for, right now, across the country. That foundation matters when you are deciding how to talk to clients and how to structure your prevention recommendations for the year ahead.

Lyme Disease: The Northeast Is Not the Only Story Anymore

The Upper Midwest and Northeast remain the highest-risk regions for Lyme disease. That is not new information. What is new — and what the 2026 forecast emphasizes with unusual specificity — is where the expansion is happening fastest.

Ohio, Kentucky, West Virginia, and parts of northern Tennessee and North Carolina are projected to experience some of the greatest expansions in Lyme disease risk compared with historical patterns. These are not traditionally high-Lyme states. They are states where veterinary practices may not have Lyme prevention as a top-of-mind conversation with every client. The forecast is a direct signal to change that before the clinical caseload confirms it.

The mechanism driving the expansion is consistent across the affected areas. Blacklegged ticks — Ixodes scapularis in the East, Ixodes pacificus in the West — are continuing their range expansion across North America. They follow forested corridors, river systems, and the deer populations that sustain their reproduction. As those corridors extend southward and westward, the tick goes with them and so does every pathogen it carries. Lyme disease is the most well-known of those pathogens, but anaplasmosis, babesiosis, ehrlichiosis caused by Ehrlichia muris eauclairensis, and Powassan virus fever travel the same vector.

Elevated Lyme risk is also expected to persist and expand in North Dakota, eastern Montana, and northern South Dakota — areas receiving westward pressure from the heavily endemic Minnesota region. And a higher-than-normal risk is expected to continue in Iowa, particularly in the southeast, driven by forested travel corridors along the Mississippi, Iowa, Cedar, and Des Moines rivers, abundant deer populations, and warming climate trends pushing the envelope of where I. scapularis can survive and reproduce.

The practical implication for practices in emerging and expanding risk areas is not subtle. In highly endemic areas, Lyme vaccination in dogs reduces both the number of positive cases and the severity of disease observed in clinical practice. Because Lyme vaccination is risk-based, practices in regions where that risk is actively increasing should be having that conversation with clients now — individually, based on lifestyle and exposure — rather than waiting for the region to hit the threshold of "endemic" before acting.

Annual screening catches trends. Consistent tick control stops transmission. Both need to be part of the protocol in any area where that risk is rising.

Heartworm: The Southeast Is Still the Core, But Nowhere Is Safe

The highest heartworm risk in 2026 remains in the southeastern United States, sustained by climate conditions that extend mosquito activity seasons, dense populations of infected reservoir dogs, and the kind of transmission pressure that has kept this disease entrenched in the region for decades.

But the more clinically urgent story in the 2026 forecast is the spread — and it is moving in multiple directions simultaneously.

Northward expansion along the Mississippi River corridor and up the Atlantic coast is placing much of the central and eastern United States, from Kansas to Maryland, at increasing risk. The Asian tiger mosquito and the yellow fever mosquito — both capable of transmitting Dirofilaria immitis — have expanded their ranges northward, bringing competent vectors into regions that were previously considered low-risk or non-endemic. A single heartworm-positive dog introduced into an area with established mosquito populations capable of transmission can seed local risk in a way that is not visible until cases start appearing in practices that were not expecting them.

This is particularly relevant for veterinarians practicing in urban centers in the Upper Midwest and Northeast. Dogs transported from southern shelters and rescue organizations arrive in these cities regularly and those dogs can be heartworm positive. The 2026 forecast is direct on this point: veterinarians in these cities should be equally prepared to diagnose, prevent, and manage heartworm disease as those practicing in traditionally high-risk areas.

Consistent pockets of elevated heartworm risk are also expected to persist in New Mexico, Colorado, Wyoming, Montana, and North Dakota — regions that have not historically been considered endemic but where practitioners are diagnosing infections more frequently than expected. Contributing factors include warmer temperatures prolonging mosquito activity, urban water use creating mosquito breeding habitats, and the movement of infected dogs introducing the parasite to new areas.

Northern California continues to see increasing risk from the northern coast through the Central Valley, driven by competent mosquito species, growing wild canid populations that serve as reservoirs, and gaps in preventive use in areas perceived as low-risk.

The phrase in the CAPC forecast that every client conversation about heartworm should include is this one: "low risk does not mean no risk, particularly for a preventable and potentially fatal disease."

Year-round prevention. Annual testing. Every dog. This is not a regional recommendation anymore. It is a national one.

Ehrlichiosis: Multiple Vectors, Expanding Range, Year-Round Risk

Ehrlichiosis in dogs is complicated by the fact that multiple Ehrlichia species are circulating, transmitted by different tick vectors, producing different geographic patterns on the same map. Ehrlichia chaffeensis and E. ewingii are transmitted by the lone star tick — Amblyomma americanum — whose range is expanding aggressively across the country. E. canis is transmitted by the brown dog tick — Rhipicephalus sanguineus — whose unique biology allows it to complete its entire lifecycle indoors, sustaining infestations and transmission year-round in homes, kennels, and shelters in hot, dry climates.

Forecasted risk for Ehrlichia species in dogs remains high throughout the southeastern, southwestern, south-central, and coastal Atlantic states. In the eastern United States, expansion of the lone star tick is driving increasing detection in a band stretching from Oklahoma and Kansas through to North Carolina and Virginia — a pattern that closely parallels where the CDC is reporting higher numbers of human ehrlichiosis cases. This is a One Health signal that is worth bringing into client conversations. The same tick exposure that puts your patient at risk is putting the owner at risk.

In the western states, the brown dog tick is driving ehrlichiosis risk in Arizona, New Mexico, Colorado, Utah, and Wyoming — and that risk is showing signs of expanding northward. Because this tick thrives in human-associated environments rather than woodland habitats, it produces a different kind of risk profile than the lone star or blacklegged tick. It does not require wooded terrain. It requires dogs. And where dogs live in close proximity — in kennels, shelters, dense residential areas — the brown dog tick can sustain transmission regardless of the surrounding landscape.

The continued northward expansion of the lone star tick is also bringing ehrlichiosis risk into the Upper Midwest and New England — Minnesota, Wisconsin, New York, Massachusetts, Vermont, New Hampshire, and Maine — regions where this tick was historically uncommon and where clinical awareness of lone star tick-transmitted pathogens may be lower than warranted.

Because multiple tick species transmit Ehrlichia species across different environments, risk is widespread across the entire United States. Year-round tick control is the baseline recommendation for every dog in every region.

Anaplasmosis: Following the Tick, Leading the Conversation

Anaplasmosis in dogs follows the same fundamental pattern as Lyme disease in the eastern United States because it is transmitted by the same vector. Where the blacklegged tick goes, Anaplasma phagocytophilum follows. The 2026 forecast reflects that parallel expansion clearly — areas forecasted for rising Lyme disease risk are also seeing parallel increases in canine anaplasmosis, and in some practices in the Northeast and Upper Midwest, the number of dogs testing positive for anaplasmosis now exceeds those testing positive for Lyme disease.

Increasing risk is projected for eastern Ohio, Kentucky, Tennessee, Virginia, and North Carolina — again mirroring the Lyme expansion. Along the West Coast, expanding populations of the western blacklegged tick — Ixodes pacificus — are driving rising canine anaplasmosis risk through northern California, Oregon, and Washington, with suburban development pushing dogs into closer contact with tick habitat in exactly the areas where this vector is most active.

In the Southwest, the picture shifts. The predominant risk in Arizona, New Mexico, and Texas is Anaplasma platys, transmitted by the brown dog tick, and the forecast notes something that warrants attention from every veterinarian practicing in that region: surveillance for A. platys challenge in dogs can serve as a useful indicator of brown dog tick activity and the potential risk of Rocky Mountain spotted fever in the same area. The CDC reports that Arizona continues to have some of the highest RMSF incidence in the country, with outbreaks closely linked to heavy brown dog tick infestations. Effective tick control for dogs in these regions carries both a companion animal and a public health implication that is worth communicating to clients explicitly.

Something New: A Novel Tick-Borne Pathogen Worth Watching

The 2026 forecast introduces something that did not appear in previous years' documents and that the veterinary community should begin familiarizing itself with now.

Researchers have recently confirmed a novel tick-borne spotted fever group Rickettsia species — Rickettsia finnyi — infecting dogs in the southeastern and midwestern United States. First detected in dogs in 2018, it has since been identified in additional canine cases. The clinical presentation resembles Rocky Mountain spotted fever. It is suspected to be transmitted by the lone star tick, whose range is expanding across large portions of the country. It has not yet been detected in humans, but its existence underscores the need for expanded surveillance of tick-borne pathogens that could impact both dog and human health.

This is not a crisis announcement. It is a signal to pay attention. A new species, a familiar vector, an expanding range, and clinical signs that look like something practitioners already know. The profession's collective surveillance capacity — those ten million plus test results flowing into CAPC each year — is how we catch these things early. Annual testing is not just about the four diseases on the forecast maps. It is about maintaining the clinical and surveillance infrastructure that identifies what is coming before it becomes endemic.

The Bigger Picture: One Health Is Not a Buzzword

The CAPC 2026 forecast is a clinical document, but it is also a public health document and it is worth reading it as both.

In 2023, multiple cases of locally acquired human malaria were reported in Florida, Texas, Maryland, and Arkansas — the first local transmission in nearly two decades. In 2025, a locally acquired chikungunya virus infection was identified in New York. Dengue virus continues to circulate in parts of Florida and Texas. West Nile virus remains active across many states. Chagas disease, caused by Trypanosoma cruzi and transmitted by triatomine kissing bugs, has established domestic transmission cycles in southern states with documented cases in both dogs and humans.

These are not imported diseases anymore. They are here. They are circulating. And the same clients bringing their dogs into your exam room are living in the same environments, being bitten by the same vectors, and experiencing the same risk expansion that your patients are.

One Health is the framework that connects canine surveillance to human health outcomes. When a dog in your practice tests positive for a tick-borne pathogen, you are not just managing that dog's health. You are contributing to the data infrastructure that tracks where disease is moving across the country. You are having a conversation with a family about the ticks and mosquitoes in their yard. You are a front line in a surveillance system that is broader than any single clinic or any single patient.

That is not an overstatement. It is what the data shows.

What to Do With This

The CAPC 2026 forecasts are not meant to create anxiety. They are meant to create preparation.

Practices in the regions identified as experiencing expanding risk — Ohio, Kentucky, West Virginia, Tennessee, North Carolina for Lyme and anaplasmosis; the Mississippi corridor and Atlantic coast for heartworm; the western states for ehrlichiosis and anaplasmosis driven by brown dog tick — should be proactively reassessing their prevention protocols before the caseload confirms the forecast.

Practices in historically low-risk areas should be having conversations about the dog that traveled, the rescue that came from the South, the outdoor lifestyle that creates exposure no regional map fully accounts for.

And every practice in every region should be testing annually, recommending year-round prevention, and using the tools CAPC has built to support those client conversations. The CAPC Parasite Prevalence Maps and forecast maps at capcvet.org are validated tools for increasing client willingness to engage in parasite prevention. The 30-day forecast maps at petdiseasealerts.org provide county-level data monthly. The daily Flea Forecast is there for the conversations that feel routine until they are not.

The maps have changed. The question is whether the conversations have changed with them.

Vet Candy covers the clinical, career, and community side of veterinary medicine for 50,000 plus veterinary professionals. Full CAPC 2026 forecast data and interactive parasite prevalence maps are available at capcvet.org. myvetcandy.com