What Diseases Can Ticks Transmit to Dogs?

Lyme disease (Borrelia burgdorferi) is the tick-borne disease most owners have heard of, and it's genuinely common in NH's tick population — New Hampshire consistently ranks among the highest-incidence Lyme states in the country, per CDC surveillance and NH DHHS tick-borne disease data. But dogs handle it differently than people do: an estimated 5 to 10% of infected dogs develop clinical signs, compared with roughly 90% of infected people. When dogs do get sick, the classic pattern is a shifting-leg lameness — pain that seems to move from one leg to another over days — along with fever, swollen joints and lymph nodes, and lethargy. A smaller share, roughly 1 to 5% of infected dogs, develop Lyme nephritis, a serious and potentially fatal kidney complication marked by vomiting, weight loss, and swelling.

Anaplasmosis is carried by the same blacklegged deer tick that spreads Lyme, so any dog at risk for one is at risk for the other. Signs overlap significantly with Lyme — fever, lethargy, joint pain — which makes it hard to tell the two apart without veterinary testing. Notably, some Northeast veterinary practices have reported anaplasmosis positive tests now matching or exceeding Lyme positives in their patient populations, a reminder that this isn't a minor, secondary concern in areas like NH.

Ehrlichiosis is transmitted by different tick species (the brown dog tick and lone star tick) and can range from mild to severe, sometimes causing serious bleeding tendencies in advanced cases. Babesiosis, a parasitic infection of red blood cells, is less commonly diagnosed in NH dogs than Lyme or anaplasmosis but is documented in the region, causing fever and signs related to anemia. Both are reasons a veterinarian's diagnostic workup — rather than owner guesswork — matters when a dog shows unexplained illness after tick exposure.

Because most tick-disease infections in dogs are silent, year-round vet-prescribed tick prevention and periodic screening tests are the practical backbone of protection, not just tick checks after the fact. Dogs are sometimes described as 'sentinels' for tick-disease risk in an area — a dog testing positive can be an early signal of local tick activity even before human cases are recognized. Ask your veterinarian what screening schedule makes sense for your dog given how much time it spends outdoors in New Hampshire.