Q: My dog just came up positive on a Lyme test. What does that mean?
A: Many veterinarians are now recommending an annual test called the 4dx test. This test screens for heartworm disease, Lyme and two other tick borne diseases called ehrlichia and anaplasma.
In order to understand this test better, we need to start by talking about what an antigen is versus an antibody. An antigen is basically a foreign substance that gets in the body and stimulates the immune system to produce antibodies. For example, when you get exposed to the cold virus, the virus is the antigen and your body will produce antibodies against this antigen.
In the 4dx test, the heartworm part of the test is an ANTIGEN test. If this part of the test comes back positive, it means that the dog has adult heartworms in her heart.
The Lyme’s test (and the ehrlichia/anaplasma test) is a different type of test. It is an ANTIBODY test. If this test comes back positive, it is most appropriate to say that your dog has been exposed to the Lyme bacteria, Borrelia burgdorferi, rather than saying your dog has Lyme’s Disease.
When we say a dog does have Lyme’s Disease, it means the dog is clinically ill from the bacteria. This bacteria can be very serious when it does cause illness. Not only can it cause an infection, it can aggravate the immune system resulting in an autoimmune problem where the body starts to attack itself. In particular, these autoimmune problems can affect the joints and kidneys leading to chronic inflammation and disease in these areas. Luckily, only 5 to 10 percent of dogs that get exposed to the Lyme bacteria ever become clinically ill.
On the 4dx test, what we see a color change on the test to show that there are antibodies. The color change is graded on a scale of one to five. A very dark color (5) means that there are a lot of antibodies in the system. A very light color (1) means that there are not as many antibodies. We presume that a dark color change means a more recent exposure, and a light color change means that the pet was exposed a while ago, but that is not necessarily always the case. One animal may just produce more antibodies then her counterpart.
The Lyme bacteria is spread by deer ticks, and it is fairly common for this test to come back positive in dogs that are not vaccinated for Lyme’s Disease, particularly if that dog travels to northern Minnesota or Wisconsin. It should be noted that there is not a consensus within the veterinary community about what the best course of action is when the test does show up positive, and the recommendations can vary widely.
What I typically recommend in this situation is to first determine if the pet is currently not feeling well. If the dog has symptoms of Lyme’s Disease (fever, lethargy, achy joints), then I will treat with a course of antibiotics. My treatment of choice is an antibiotic called doxycycline. For a while doxycycline was not available to veterinarians. Then when it did become available again, it came back at a new improved price that was about 100 times more expensive then it was before. If doxycycline doesn’t make financial sense to treat a certain pet, there are other antibiotics that have been shown effective for Lyme’s Disease, including minocycline, amoxicillin, and a long lasting injectable antibiotic called Convenia.
If the pet is not ill, then I typically recommend a urine sample to check to see if the kidneys are leaking protein. This is an early indicator of kidney disease. If this test is negative, then the only treatment I typically recommend is good tick control going forward. The products Frontline and Certifect are my tick protection of choice. There are other products available for tick control, but I just don’t think they are as effective or last as long. The most important thing to note when using a tick control product on a dog is to begin using the product early in the tick season. Tick eggs hatch as soon as the temperature gets above freezing. t is always a shock when we see ticks out and there is still snow on the ground, but it can happen. If we are having a mild winter, it is safest to use tick control even during the winter months.
Dr. Teresa Hershey is a veterinarian at Westgate Pet Clinic in Linden Hills. Email her your pet questions at firstname.lastname@example.org.