Warm Falls Fuel Surge in Anaplasmosis as Tick Season Expands Year-Round

As fall temperatures linger above freezing across the Northeast, anaplasmosis is no longer a summer concern — it’s a year-round threat. Cattle herds, pets, and humans are all at higher risk as the blacklegged tick (Ixodes scapularis) extends its active season, fueled by warmer winters and delayed frosts. The shift isn’t subtle: in 2023, cases of tick-borne illnesses like anaplasmosis occurred 11 months out of the year — up from just 2.2 months before 2000. And it’s not just Lyme disease. Dr. John Ross, an assistant professor of medicine at Harvard Medical School, says the pattern is unmistakable: "It’s going from something we just see a case in July and August here and there to something we’re essentially seeing year-round."

Why Fall Is the New Peak Season

Unlike Lyme disease, which peaks in late spring and early summer with nymph ticks, anaplasmosis surges in the fall. That’s when adult female blacklegged ticks — the ones that carry Anaplasma phagocytophilum — are actively seeking their final blood meal before winter. They need that meal to survive, lay eggs, and ensure the next generation. The Vermont Department of Health confirms this: anaplasmosis is the second most common tick-borne illness in the state, and since 2015, Vermont has had the highest annual incidence of the disease in the entire U.S. The twist? Ticks don’t die after the first frost. They go dormant. And when daytime temperatures creep back above freezing — even in November — they wake up. One farmer in central Maine told me he lost three cows last November to anaplasmosis. "We thought the tick season was over," he said. "Turns out, the ticks were just waiting for a warm afternoon."

Climate Change Is Rewriting the Rules

New England is warming faster than 98% of the planet. That’s not speculation — it’s data from NOAA and the Johns Hopkins Bloomberg School of Public Health. Thomas Hart, an epidemiologist there, calls 2025 a "hot year for ticks." The CDC recorded 89,000 new Lyme cases in 2023 alone. But anaplasmosis? It’s climbing just as fast. And it’s spreading west. The Companion Animal Parasite Council (CAPC), which tracks canine tick-borne diseases since 2012, reports that in some veterinary clinics in Minnesota and Wisconsin, more dogs are testing positive for anaplasmosis than Lyme. The risk is now expanding into eastern Ohio, Kentucky, Tennessee, Virginia, and North Carolina — areas where the disease was nearly unheard of a decade ago. The reasons? Warmer winters mean fewer tick die-offs. Faster maturation. Longer activity windows for nymphs in spring and fall. And deer, mice, and other hosts — which carry ticks — are surviving better in milder conditions. "It’s a perfect storm," Hart says. "Climate change didn’t create ticks. But it gave them a runway."

What This Means for Farmers and Pet Owners

For cattle producers, anaplasmosis means anemia, weight loss, reduced milk production, and sometimes death. A single infected cow can cost a farm $1,200 in treatment and lost productivity. Vaccines exist, but they’re not always effective against all strains. Many producers now rely on monthly tick preventatives and routine blood tests. Pet owners are seeing the same trend. Dogs in Vermont and New Hampshire are now being tested for anaplasmosis as routinely as for Lyme. "We used to test in May," says Dr. Lisa Chen, a vet in Burlington. "Now we test in March, July, and November."

How to Protect Yourself and Your Livestock

Experts agree: vigilance is non-negotiable.

• Wear long sleeves and pants, tucking them into socks when walking through tall grass or wooded areas.
• Use EPA-approved tick repellents on skin and clothing.
• Check yourself, your children, and your pets thoroughly after being outdoors — especially behind ears, under arms, and around the waist.
• For livestock: apply acaricides during high-risk months (April–November), keep pastures mowed, and consider fencing to reduce deer access.
• Remove leaf litter and woodpiles near homes — prime tick habitat.

And here’s the hard truth: if you wait for frost to mean safety, you’re already late. Ticks don’t follow calendars. They follow temperature.

The Bigger Picture

This isn’t just a regional problem. It’s a national health infrastructure challenge. The CDC estimates only 10% of tick-borne disease cases are officially reported. Many go undiagnosed or misdiagnosed as the flu. Anaplasmosis can be treated with antibiotics — but if missed, it can lead to kidney failure, respiratory distress, and death, especially in the elderly or immunocompromised. The expansion of these diseases is outpacing public health responses. Fewer rural clinics have the tools to test for anaplasmosis. Insurance often doesn’t cover broad tick panels. And awareness? Still lagging. "We’re not ready," says Dr. Ross. "We’re still treating this like a seasonal nuisance. It’s becoming a chronic public health crisis."

What’s Next?

The Centers for Disease Control and Prevention is funding new surveillance programs in 12 states, including Vermont and Maine, to map tick populations and disease hotspots in real time. A new federal grant in 2025 will expand veterinary diagnostic networks to help farmers and pet owners get faster results. Meanwhile, researchers at the University of Maine are testing a new environmental model that predicts tick activity based on soil temperature, humidity, and deer migration patterns. Early results suggest they can forecast high-risk zones up to six weeks in advance. But for now, the message is simple: don’t let your guard down when the leaves start falling. The ticks aren’t done.