Visiting Veterinarian : Diagnosing Lyme in dogs is an imprecise science for vets
Staring at the small plastic device on the counter, I watched with chagrin as two blue dots materialized in the tiny window. Here we go again, I groaned. No, at 57, the blue dots didn't herald a belated visit from the stork. This was a 4DX test used to screen dogs for antibodies to various organisms including Borrelia burgdorferi, the bug that causes Lyme disease.
My patient was Tolstoy, a young Australian shepherd perched nervously on my table for a routine annual visit. I had been about to pronounce him fit as a fiddle... until those pesty blue dots appeared. "Have a seat," I invited his dad before launching into an explanation about "asymptomatic Lyme-positive."
Unless you fell off the ferry yesterday, you probably have some experience with Lyme disease. Maybe you've had it yourself. Or your kid has. Twice. Maybe you think you have it now, but your doctor swears you don't. Or you know someone seriously disabled by it. Diagnosis and treatment, acute versus chronic, this is too big a can of worms to fully explore today, but let's look at a classic symptomatic canine case, then compare with Tolstoy.
Let's call our other pooch Dogstoevsky. Unlike Tolstoy, Dogstoevsky has a fever and a swollen ankle. He's limping and feeling lousy. In other words, he has symptoms. I run a 4DX. He has always been negative in the past, but today he comes up Lyme-positive. I'm comfortable making a presumptive diagnosis of Lyme infection.
At this point in time, there is no definitive diagnostic test for Lyme in dogs. If Dogstoevsky has consistent clinical signs and a history of tick exposure in a Lyme-endemic area, if other diseases have been ruled out and he responds to treatment, then we can say "Yup, he probably had Lyme." In dogs it takes two to five months from the time Dogstoevsky is bitten by an infected tick until he shows clinical symptoms, so I don't pay too much attention to whether an owner has observed ticks on my patients. I just figure any dog that lives here can be assumed to have tick exposure.
There is little doubt, however, that we over-diagnose Lyme in dogs. There may be many other explanations for Dogstoevsky's symptoms. As I often tell clients "not every limping dog has Lyme."
According to the American College of Veterinary Internal Medicine (ACVIM) Small Animal Consensus Statement on Lyme Disease in Dogs (published in 2006 in the Journal of Veterinary Internal Medicine), although 90 percent of humans infected with Borrelia burgdorferi (Bb) develop clinical symptoms, in dogs the scenario is dramatically different. Experimentally infected puppies show typical symptoms of fever, loss of appetite, and arthritis, but as many as 95 percent of dogs naturally exposed to Bb remain asymptomatic.
Veterinarians in the field report all kinds of problems in Lyme-positive dogs including kidney, heart, and neurological disease, but no one has definitively proven cause and effect. But in areas with high incidences of Lyme, veterinarians often prefer to err on the side of over-treating, usually prescribing doxycycline, the same antibiotic used in humans.
"He got better right away on that doxy," you say. "So it must have been Lyme, right?" Well, not necessarily. Besides being an antibiotic, doxycycline also has anti-inflammatory properties that can make a dog feel better even if he doesn't have Lyme.
Now let's talk Tolstoy. He's asymptomatic Lyme-positive. Asymptomatic means without symptoms. In other words, Tolstoy appears completely healthy despite the fact that he tests positive for Lyme on the 4DX. Is he infected? Or does he just have antibodies? Lyme vaccination does not affect the test so we can say definitely he has been exposed to the Bb organism.
Should we treat him? How will we know if our treatment does any good? If we don't treat him, will he eventually get sick? Should he continue to have Lyme vaccines?
Don't quote me, but your guess is as good as mine. Okay, I'm kidding...sort of. As far as I can see, we don't know a helluva lot about how this all works. According to the ACVIM Consensus Statement there is no conclusive evidence that the majority of asymptomatic Lyme-positive dogs will ever get sick or that treatment is useful. Hence many veterinarians never ever treat asymptomatic Lyme-positive dogs. But those vets probably don't live on Martha's Vineyard and have never taken their golden retriever for a walk at Cedar Tree Neck in April.
On the other end of the spectrum, some vets treat every single asymptomatic Lyme-positive dog "just in case." I'm not a big fan of this approach either. Lots of these dogs remain Lyme-positive forever. Are we going to treat them all annually? Or every time we run a 4DX test? Overuse of antibiotics leading to resistant organisms is a big cause for concern and a good reason not to routinely treat every asymptomatic case.
The bottom line is that those of us practicing veterinary medicine in areas with high incidences of Lyme disease have to formulate our own, personal recommendations for dealing with the Tolstoys that we see every week. We can utilize ancillary tests, like the Lyme Quantitative C6 Antibody Test, which gives a number indicating a specific antibody titer rather than just a blue dot. Although the magnitude of the titer may not predict whether Tolstoy will ever develop clinical disease, at least it gives us some kind of benchmark to work with. Many veterinarians run a baseline QC6 level on first-time asymptomatic positive dogs, treat with doxycycline, and repeat the QC6 in three to six months, looking for a 50 percent drop, post-treatment.
It may also be useful to monitor chronically Lyme-positive asymptomatic dogs for kidney disease, especially golden and Labrador retrievers, who seem to have a breed-specific susceptibility to such sequella. There isn't a clear right or wrong, at least not with our current level of knowledge. If your Tolstoy is asymptomatic Lyme-positive, discuss it with your veterinarian and decide together what approach to take.