Diagnosis and treatment for an asymptomatic dog that tested positive for Lyme and anaplasmosis infections.

The following case is taken from actual medical records. Names, photographs, and minor details have been changed to maintain client-patient confidentiality.


Archie, a 1-year-old mixed-breed, neutered male dog, was adopted with no history of health problems. He had been vaccinated as a puppy for DHPP and rabies. At the initial exam, Archie was thin but appeared healthy. His vaccines were updated and he was tested for heartworms, Lyme disease, and anaplasmosis with the IDEXX SNAP® 4Dx® test.

Archie proved negative for heartworm but positive for Lyme Borrelia burgdorferi and canine anaplasmosis infections. The antibody test indicated that Archie was infected with the Lyme spirochete and anaplasmosis bacteria at some point – most likely the previous "tick season." It is not unusual that Archie showed no clinical signs because many dogs will not become symptomatic until several months after infection.

Because he was asymptomatic for both Lyme and anaplasmosis, it was decided to evaluate him during the next few months, rather than treat him. However, because he lived in an endemic Lyme disease area, he was given a Lyme vaccination at this time, not intended to treat, manage, or clear infections he already had, but to help prevent new infections.

  • During the 3 months after the initial exam, there were no clinical signs and the CBC profile was normal
  • Four months after the initial exam, Archie developed acute lameness of the right front leg after jumping off a chair
  • During the next 2 days, Archie began limping on his left front leg, his appetite diminished, he refused to move, and was depressed
  • Archie presented as a weekend emergency and a physical exam was performed
  • Results showed effusion palpable in multiple painful joints; CBC profile and joint taps were performed

Anaplasmosis is an acute disease and dogs typically get sick or manage the infection without treatment. However, experimental research suggests that chronic infection may be possible. Lyme disease is a chronic infection and most dogs will not be able to clear the infection on their own.

There is much debate on whether to treat or not to treat a positive asymptomatic dog for Lyme disease and/or anaplasmosis. Archie's veterinarian reports that 25% of Lyme-positive dogs in his practice develop clinical signs 12–14 months after infection.

Ultimately, the decision is up to the practicing veterinarian and the pet owner. Regardless of the decision to treat or not treat, tick control and Lyme immunization are recommended.


  • CBC showed anemia (30.8% Hct) and profile showed elevated ALP (312 U/L)
  • Joint taps showed many neutrophils and increased protein in joint fluid
  • Development of suppurative polyarthritis is the most common clinical presentation of Lyme and anaplasmosis
  • Thrombocytopenia, anemia, leukopenia, and elevated ALP are the most common findings with anaplasmosis
  • Lyme infection alone typically doesn't cause CBC and profile abnormalities


  • Doxycycline 5–10 mg/kg BID for 30 days
  • Within 48 hours, Archie no longer showed lameness and played normally
  • Two weeks later, CBC and profile were normal


  • Assess clinical response and recheck CBC in 7 to 10 days for response to anaplasmosis treatment


  • Annual screening for Lyme disease is important, whether the dog is symptomatic or asymptomatic
  • Dogs testing positive but asymptomatic for Lyme disease and anaplasmosis (co-infections) are at increased risk for developing clinical disease
  • Regular screening can identify infections in the subclinical phase and help with management strategies
  • Positive, asymptomatic dogs should be vaccinated with a Lyme vaccine to prevent future infection
  • Some dogs will become symptomatic later
  • Some dogs will never have clinical signs
  • Once a dog is C6 positive, it will usually remain C6 positive for life, even if the infection is under control
  • Preventive strategies such as tick control and Lyme vaccination can help reduce the risk of Lyme disease


  • Archie's veterinarian in Minnesota recommends the Lyme vaccine to every dog that is seen in the clinic


Learn the facts about how to assess risk by geography and exposure to deer ticks.


Lyme Disease is largely preventable through tick control and vaccination. Get important details.


Read about real dogs that were diagnosed with Lyme disease.