Veterinarians are finding that canine Lyme disease is more common than we'd thought. New testing techniques have discovered many infected dogs, yet what to do with them is uncertain.
Lyme disease (specifically the Borrelia burgdorferi bacterium) is spread by ticks. Your dog's risk for contracting it therefore depends on tick exposure. A dog who lives in an apartment and walks only on concrete probably will never pick up a tick. But a dog who goes for walks in any wooded area could be exposed. The risk also hinges on where you live: Lyme disease has been found in all 48 contiguous states, but the Northeast and the upper Midwest are considered hot spots for the organism.
If your dog does pick up a tick, will he get Lyme disease? Not all ticks carry Borrelia so you can't be sure, but human-health data can help determine the likelihood of infection. Local health authorities track Lyme disease in people and can tell you where it is prevalent; from that you can determine if ticks in your area carry the Lyme-causing bacterium. You also can ask local veterinarians how many canine cases they diagnose.
Because Lyme disease is relatively new in dogs, there are still some facts we're unsure about. Even test results can be difficult to understand. If a dog has a positive test, it means he has antibodies to Borrelia burgdorferi in his bloodstream. But does this mean he has Lyme disease? Should he be treated? These are not easy questions to answer.
Clinical signs develop in only about 1 0 percent of infected dogs. They occur two to five months after the infection and may include lameness (due to polyarthritis), enlarged lymph nodes (lymphadenopathy), lethargy, and fever. It is common for these signs to resolve by themselves within a few days, though some dogs require antibiotics to recover fully. Less common syndromes associated with canine Lyme infection include renal disease (Lyme nephritis), heart disease (myocarditis), and neurological disease. It is not known whether or not dogs get the devastating recurrent disease syndromes typical of human infections.
We do know that if a dog has clinical symptoms of Lyme disease he needs treatment. This consists of antibiotics, usually amoxicillin or doxycycline, for four to six weeks. But if an apparently healthy dog has a positive test, what should be done? Does the dog have, or will he ever develop, symptoms of Lyme disease?
A large percentage of dogs-up to 70 percent in some places- have antibodies against Borrelia in endemic areas where ticks carry the organism. Despite this level of exposure, very few of these dogs show clinical signs of Lyme disease. Many mount an immune response and eradicate the Borrelia bacterium from their bodies, but their blood tests positive for the very antibodies that cleared the Lyme disease organism.
Some veterinarians believe they should treat all dogs with a positive test whether they show symptoms or not.
Others choose to treat only dogs with a high level of antibodies in the bloodstream. A third group reserve treatment for dogs who have both clinical symptoms and positive blood tests.
Dilemmas over testing and treatment for Lyme disease can be avoided by preventing infection. Frequent tick removal is the best way to prevent Lyme disease. A tick may take up to 12 hours to attach to a dog, and a further 18 to 24 hours to transmit Borrelia. This means that if you remove ticks from your dog daily, you will likely prevent transmission of the infection. If you do tWice-daily tick checks, you will almost certainly prevent Lyme disease.
If you can't do regular tick checks, another option is to prevent transmission by repelling and killing ticks. Your veterinarian can prescribe effective topical insecticides to control ticks.
The most widely publicized way to prevent Lyme disease is through vaccination. Two kinds of vaccines are available-a whole-cell bacterin that consists of the entire (killed) Borrelia organism, and a recombinant outer surface protein A (OspA) vaccine containing just one part of the Borrelia bacterium. Both are effective and safe.
Vaccines stimulate the production of antibodies to the OspA protein. As a feeding tick ingests the blood of a vaccinated dog, the vaccine-generated antibodies against OspA end up in the tick's gut. They bind to the
Borrelia organisms (found in the tick's stomach) and inactivate them. This reaction occurs only in the tick. If", the bacterium reaches the dog, its surface proteins change to OspC, so the vaccine antibodies are ineffective.
Should you have your dog vaccinated against Lyme disease? The answer will depend primarily on the prevalence of Lyme in your area. In some areas of the northeast United States, 50 percent of dogs are infected with the disease organism annually. But if you live in a non endemic area, where Lyme disease is not a problem, vaccination is not justified.
Some veterinarians question whether canine Lyme disease is a severe enough condition to warrant vaccination, no matter how many dogs are infected. If symptoms can be successfully treated with antibiotics, and if 90 percent of dogs don't develop symptoms after infection anyway, do they need vaccine protection?
In places where the disease is endemic, Dr. Richard E. Goldstein, a veterinarian from the College of Veterinary Medicine at Cornell University, recommends vaccination of all dogs. He and many other veterinarians believe dogs should be given protection because we don't yet know the Significance of Lyme nephritis nor whether chronic recurrent Lyme disease occurs in dogs.
Your veterinarian can inform you about vaccination protocols based on her personal understanding of Lyme disease and the prevalence of infection in your area.
As you can see, we still have a long way to go before we fully understand canine Lyme disease. In humans, the long-term consequences of Borrelia burgdorferi infection are well known. But we don't know if dogs suffer in the same way, and we may not know for a long time. For now, protect your dog by implementing a tick-control program, and consider vaccination if you live in an endemic area.