Testing for Lyme Disease in Dogs

Implications of a Positive Test for Borrelia borgdorferi in a Dog

Oct 3, 2009

In a sick dog, a positive Lyme disease test indicates a need for treatment. When a healthy dog tests positive, the proper course of action is more difficult to determine.

Annual testing for Lyme disease is commonly performed in areas where the disease is endemic. However, there is often confusion about the significance and meaning of a positive test for Lyme disease, especially in dogs which appear to be healthy.

Canine Lyme Disease is a Tick-Borne Disease Caused by Borrelia borgdorferi

The ticks most commonly responsible for spreading canine Lyme disease are the Ixodes species of ticks and Amblyomma americanum. Lyme disease is actually caused by a ricketssial organism known as Borrelia borgdorferi. The most common symptoms seen in dogs with Lyme disease are fever, lameness which may shift from one leg to another, joint pain and lethargy. On rare occasions, a kidney form of Lyme disease is also seen, which is generally much more serious and more difficult to treat.

Commonly Used Tests for Lyme Disease in Dogs

The most commonly used tests for dogs are patient-side tests known as the SNAP 3DX® and SNAP 4DX®. These tests require a small blood sample and simultaneously test for canine heartworm disease, canine ehrlichiosis (Ehrlichia canis) and, in the case of the SNAP 4DX® test, canine anaplasmosis (Anaplasma phagocytophilum). Both of these tests measure the C6 peptide for Lyme disease, which is an antibody that develops in the dog's blood in response to exposure to Borrelia borgdorferi.

Another blood test which actually quantifies the C6 peptide is also available. However, the levels of C6 peptide antibody have not been found to correlate with the degree of illness, if any, seen in infected dogs. Healthy dogs can have extremely high titers for the C6 antibody.

What does a Positive Lyme Disease Test Signify for a Dog?

Many dogs which test positive for Lyme disease on any of these tests never actually show symptoms of Lyme disease. It is estimated that as many as 90-95% of dogs testing positive for Lyme disease remain asymptomatic. A Lyme disease test in an individual dog can remain positive for long periods of time, often for months or even years.

A positive Lyme disease test does indicate that ticks capable of transmitting Lyme disease have fed on the dog, which also indicates that there is the possibility of transmission of other tick-borne diseases which may adversely affect the dog's health.

Lyme disease testing in dogs is also frequently used as an indicator of the potential for disease in the human population in the area. Therefore, testing for canine Lyme disease can serve as a sentinel for human Lyme disease infection.

How Should a Dog Testing Positive for Lyme Disease be Treated?

Dogs which are showing symptoms consistent with Lyme disease should be treated with antibiotics and most dogs respond well to antibiotic therapy. However, dogs with the kidney form of Lyme disease are difficult to treat and this condition, though rare, can become fatal.

The antibiotic most commonly used for treating Lyme disease in dogs is doxycycline, but other antibiotics, such as amoxicillin and ampicillin, are also used and are effective as well. However, in many dogs, some Borrelia organisms will survive the antibiotic treatment, even though the clinical signs of Lyme disease resolve. Some dogs may also develop chronic Lyme disease.

Treating asymptomatic dogs which test positive for Lyme disease is less straightforward. Although treating these dogs with antibiotics usually results in lowered C6 antibody levels, it is unlikely that all Borrelia organisms will be killed. It is currently unknown whether treatment with antibiotics can actually halt the development of active Lyme disease. It is also unknown whether Lyme-positive dogs treated with antibiotics may still become chronic carriers of Lyme disease.

Asymptomatic Lyme-positive dogs should have blood and urine testing performed to monitor for renal disease and should be observed for other symptoms of Lyme disease regardless of whether or not they are treated with antibiotics.

Should All Dogs be Tested for Lyme Disease Yearly?

For dogs experiencing symptoms of lameness, lethargy, joint pain, fever, kidney disease, or other signs which may be caused by Lyme disease, almost all veterinarians agree that a Lyme disease test is indicated and proper antibiotic therapy necessary if the test is positive.

For asymptomatic, healthy animals, veterinary recommendations vary depending on the veterinarian and the geographic location.

Lyme disease in dogs continues to be a somewhat confusing topic with a variety of different perspectives in regards to testing dogs and treating those which have positive test results. Dogs which are clearly showing symptoms of Lyme disease obviously need to be treated for the disease. However, in healthy dogs with positive Lyme disease test results, there is no evidence that antibiotic therapy actually helps to prevent disease. At the current time, it is not known whether there is any benefit to treating these dogs prophylactically with antibiotics. For this reason, there is also some debate as to whether there is any value in routinely testing healthy dogs for Lyme disease, even though the test is performed commonly and routinely in many practices.

Liang FT, Steere AC, Marques AR, Johnson BJB, Miller JN, Phillipp MT. Sensitive and specific serodiagnosis of Lyme disease by enzyme-linked immunosorbent assay with peptide based on an immunodominant conserved region of Borrelia burgdorferi VIsE. J Clin Microbiol. 1999;37(12):3990—96.

Phillipp M, et al. Antibody response to IR6, a conserved immunodominant region of the VIsE lipoprotein, wanes rapidly after antibiotic treatment of Borrelia burgdorferi infection in experimental animals and in humans. J. Infect. Dis. 2001;184(7):870—78.

The copyright of the article Testing for Lyme Disease in Dogs in Pet Diseases is owned by Lorie Huston. Permission to republish Testing for Lyme Disease in Dogs in print or online must be granted by the author in writing.