Dear Doctor – Testing positive for Lyme disease even with no symptoms

Letter to Tufts Veterinarians


Q I have a healthy 5-year-old female golden retriever who was treated for Lyme disease last year but tested positive again this year even though she shows no signs of illness. My vet was not concerned and suggested we could wait until next year and test again.

I am puzzled by the apparent contradiction between testing positive after treatment and her lack of any symptoms. Should I be concerned?
Irene Desmond
Gloucester, MA

Dear Ms. Desmond,
A What to do with a positive Lyme test result in an asymptomatic dog is somewhat controversial. “There are reasons to treat, reasons not to treat, and no clear answers,” says Michael Stone, DVM, who conducts research on tick-borne diseases in companion animals at the Cummings School.

Lyme disease, the most common tick-borne disease in the Northern hemisphere, is caused by infection with bacteria known as Borrelia burgdorferi. Infection is diagnosed not by identification of B. burgdorferi itself but instead by detection of antibodies against B. burgdorferi. Interestingly, not all dogs infected with the bacterium or its antibodies become clinically ill. In fact, antibodies are detected in approximately 95 percent of all dogs living in Lyme, Connecticut; however, only 3 percent of these patients ever show clinical signs of illness. Thus, the controversy: if an asymptomatic pet is discovered to have antibodies against B. burgdorferi, is treatment justified?

One reason to treat might be to avoid the development of illness in the future, although we have no studies at this point to suggest treatment of an asymptomatic pet is beneficial. Two reasons not to treat include the potential overuse of antibiotics, which could lessen their effectiveness, and the additional expense incurred by pet owners.

What is a pet owner to do? Feel confident in following your veterinarian’s recommendation. Theoretically, lowering your pet’s antibody level could be of benefit, if you don’t mind the expense. However, if you go with your vet’s advice and decide not to treat, you’re not being remiss. At our current state of understanding, either approach is medically justified.


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