Lyme & Heartworm Are Moving: Is Your Pet at Risk in 2025?

Parasites on the Move

Across the United States (and even parts of Canada), disease-carrying parasites like ticks and mosquitoes are spreading into regions once considered “safe” for pets. Climate shifts, changing wildlife patterns, and pet travel have expanded the habitats of ticks that carry Lyme disease and mosquitoes that transmit heartworm.

The result: a growing threat of these diseases in areas that historically saw little to none. This isn’t just a pet problem – it’s a One Health issue, since rising trends in pets often mirror those in humans. Below, we break down how Lyme and heartworm risks are expanding, why experts are concerned, and what it means for protecting dogs and cats in 2025.

Expanding Risk in Once-“Safe” Regions

Lyme disease and heartworm are no longer confined to their old geographic strongholds. Recent data and forecasts show that previously low-risk areas are now on alert.

• Lyme disease: The CDC notes that since the 1990s, the range of reported human cases has broadened significantly. Over 89,000 human cases were reported in 2023 alone – a record high reflecting both improved surveillance and real spread.
• Heartworm: Once mostly a Southern U.S. issue, heartworm has now been found in all 50 states, with new infection hotspots emerging where it was once rare.

What’s Driving the Spread?

• Climate change: Warmer temperatures and longer summers allow ticks and mosquitoes to survive in higher latitudes and elevations.
• Invasive mosquitoes: Species like the Asian tiger mosquito (Aedes albopictus) have expanded northward, bringing heartworm risk.
• Wildlife & travel: Deer populations fuel tick growth, while coyotes and other canids act as reservoirs for heartworm. Pets traveling or relocating spread parasites into new regions.
• Gaps in prevention: Missed doses of preventatives create opportunities for parasites to establish in new communities.

Lyme Disease on the Move

Lyme disease in dogs (and humans) has traditionally been centered in the Northeast and Upper Midwest. Those remain hotspots, but the edges of Lyme’s territory are pushing outward.

• Connecting the Coasts: Rising cases in Indiana, Ohio, Illinois, and Michigan are bridging the once-separate Northeast and Midwest hotspots.
• Southward creep: Ticks carrying Lyme have been detected in Tennessee and North Carolina, expanding risk in the Appalachians.
• Heading north: Southern Canada (Ontario, Quebec, New Brunswick) is now reporting more cases as ticks cross the border.
• Westward spread: Higher risk forecasts are emerging in the Dakotas, Iowa, and Kansas, with cases also appearing in northern California, Oregon, and Washington.

One Health Perspective

Ticks don’t discriminate. The same ticks biting dogs bite people, making pets important sentinels. Areas with high canine Lyme incidence nearly always align with high human case rates. This is why veterinarians and public health officials now share surveillance data – a rise in Lyme among pets is a warning for the whole community.

Fortunately, tools exist: highly effective tick preventatives and a Lyme vaccine for dogs. But experts stress that these must be used proactively in emerging risk zones, not after outbreaks are already entrenched.

Heartworm: A Growing Threat Further North and West

Heartworm, caused by the mosquito-borne parasite Dirofilaria immitis, was once mostly a problem in the Southeast. Today, the threat is expanding well beyond the “heartworm belt.”

• Pushing north: Mosquitoes now carry heartworm up the Mississippi River corridor, through Tennessee, Kentucky, and into the Mid-Atlantic.
• New hotspots: Unexpected increases are appearing in the Pacific Northwest (Washington, Oregon), the Northern Plains (North Dakota, Montana), and even high-elevation states like Colorado and Wyoming.
• West Coast: Northern California’s Central Valley is now considered a high-risk pocket.
• Southwest: Parts of New Mexico and Arizona are reporting higher-than-expected rates.

Why the spread? Mosquito vectors are adapting and expanding, aided by warming climates and pet movement. Even one infected dog in a community can seed local mosquitoes, elevating risk for every other pet nearby.

The paradox: heartworm is nearly 100% preventable with medication, yet cases keep rising due to inconsistent prevention.

One Health Angle: Pets and People Share the Risk

Lyme and other vector-borne diseases demonstrate the close link between pet and human health.

• Dogs as sentinels: Pets often encounter ticks and mosquitoes first, warning of risks in the environment that people also face.
• Environmental change: Expansion of parasite habitats increases exposure for both pets and people. For example, mosquitoes carrying heartworm also carry human diseases like West Nile virus.
• Zoonotic risks: While humans don’t typically get heartworm, ticks and mosquitoes that infect pets also transmit pathogens that affect humans.

Veterinary and medical communities are increasingly collaborating, recognizing that what makes pets sick often signals threats to people too.

Preventive Care Lags Behind the Spread

Despite rising risks, many pet owners remain inconsistent with parasite prevention.

• Heartworm: Surveys show over 68% of U.S. dogs leave veterinary visits without a preventive. Only one-third are consistently protected, explaining why infection rates have climbed from ~800,000 cases in 2001 to over 1.2 million today.
• Ticks & Lyme: Preventatives and vaccines are underutilized, especially in areas where Lyme is emerging. Owners often assume “we don’t have ticks here” – until infections prove otherwise.
• Education gap: Many owners are unaware that parasite maps have shifted. Veterinarians stress that “low risk is not no risk,” urging year-round prevention in all states.

Encouragingly, communities with higher compliance have seen reduced infection rates – proof that prevention works if consistently applied.

Protecting Pets in a Shifting Landscape

For veterinarians, the expanding parasite map means updating protocols. For pet owners, it means rejecting outdated assumptions about risk.

Key takeaways for 2025:

• No region is “safe” anymore – Lyme and heartworm are on the move.
• Year-round heartworm prevention is recommended for all dogs (and cats, where appropriate).
• Consistent flea/tick preventatives and Lyme vaccination (in at-risk areas) are crucial.
• Rising pet parasite trends often foreshadow human risks – protecting pets protects families too.

Parasites don’t respect borders or climate norms. Staying vigilant, investing in prevention, and monitoring disease trends are the best tools we have. In the face of these moving targets, prevention truly is the best medicine.

Sources

• Companion Animal Parasite Council (CAPC) – 2025 Pet Parasite Forecasts (Lyme & Heartworm spread, One Health data) – capcvet.org
• American Veterinary Medical Association (AVMA) – Heartworm incidence, prevention compliance, and climate-related spread – avma.org
• Centers for Disease Control and Prevention (CDC) – Lyme surveillance and case trends – cdc.gov
• Veterinary Practice News – West Coast Lyme and heartworm observations – veterinarypracticenews.com
• Shelter/parasite compliance reports – avma.org