THE FACTS ABOUT LYME DISEASE
Undoubtedly, we’ve all heard of Lyme Disease. Unfortunately, any subject that spends time in the media spotlight is apt to be shrouded by misinformation and misunderstanding. Hopefully, this article will lift that shroud and provide the current scientific knowledge regarding Lyme Disease, thus allowing you to make a better informed decision for your pet. This information is a summary of an article from the November 1, 2003 issue of the Journal of the American Veterinary Medical Association, written by Dr. Curtis Fritz and Dr. Anne Kjemtrup of the California Department of Health Services.
Lyme Disease is caused by a spirochete bacteria named Borrelia burgdorferi, abbreviated as B. burgdorferi. This spirochete uses hard ticks, also known as deer ticks, to spread from small mammals (i.e. mice and squirrels) to large mammals (i.e. humans, dogs, horses, deer, etc.). The deer tick is considered a three host tick, meaning that at each stage of its life (larvae, nymph, and adult) the tick takes a blood meal. Larval and nymphal stages of the deer tick, which are commonly found in leaf litter, acquire the spirochete B. burgdorferi from feeding on infected white footed mice. These mice, along with birds and lizards, act as reservoirs of infection of B. burgdorferi. B. burgdorferi is passed from larval to nymphal to adult ticks as they mature. Greater than 50% of deer ticks are infected with the Lyme’s causing organism! As an adult, the deer tick then climbs to the tips of the grasses and waits for a large mammal to brush up against it. Once attached to the animal, it takes 48 hours before the tick transmits the Lyme causing spirochete to the person, dog, deer, or other large mammals.
Dogs don’t develop all the same symptoms of Lyme Disease as people. Two to five months after infection, dogs most commonly develop lameness accompanied by a fever and inappetence. The lameness is usually caused by arthritis in the ankle or wrist joints. Young dogs are more susceptible to infection than older dogs. If your dog is limping, acting sick, and has a fever, he may very likely have Lyme Disease! Rarely, dogs can also develop kidney failure due to Lyme Disease, in addition to neurologic problems and heart problems. However, not all infected dogs will develop symptoms of Lyme Disease.
Diagnosing Lyme Disease in dogs is a complicated issue. To confirm a diagnosis one not only has to have a positive test result, but also a history of tick exposure, compatible symptoms, exclusion of other diseases, and possibly response to antibiotic treatment. “Laboratory results alone are not prima facie evidence of infection but must be interpreted with regard to the pretest probability of the disease existing in the patient.”
Recently a new antibody test (a test that measures the response of the immune system to the Lyme organism) has been developed for use in the veterinary clinic to test for Lyme Disease (SNAP 4DX). However, “detection of antibody against B. burgdorferi is not definitive evidence of active or incipient Lyme Disease, nor an indication of the need for treatment. ” If the 4DX test is positive for Lyme disease and the dog is showing symptoms, a quantitative C6 antibody test should be perfomred. This test is more specific for detecting the presence of the Lyme organism. Once dogs are exposed to B. burgdorferi they may continue to test positive for months, years or indefinitely following infection and resolution of the disease. The tests just cannot differentiate between dogs with active infection and those with antibodies from an earlier exposure. One study actually found that 89.6% of healthy dogs tested positive for B. burgdorferi exposure! Blood tests for Lyme Disease should be reserved for dogs with a history and clinical signs that are highly suggestive of active Lyme Disease.
If your dog should develop symptoms of Lyme Disease and has a positive test result, prompt treatment with antibiotics (doxycycline or amoxicillin) for 30 days will resolve the disease. However, a course of antibiotics based solely on the basis of a routine test result is unlikely to reduce the chance of getting sick or in preventing reexposure. Therefore, treatment should only be given to dogs with symptoms of Lyme Disease, a positive test result and a high C6 antibody.
The best prevention is to prevent exposure to ticks. Avoid grassy or wooded areas, or areas with leaf litter especially during the late Spring and early Fall. Check your dog daily after being outside during tick season. Look closely around the head and ears, the areas where ticks usually attach. Preventic collars and Frontline can also be used to control ticks on your pet, but remember these products are toxic and are not used on people. Do you really want to put something on your pet that is not approved for use on yourself? There are natural tick repellents on the market. These can help reduce the overall number of ticks on your pet, but still require a thorough “tick check” after going into a tick infested area. Interestingly, a swath of mulch placed between wooded areas and lawns can provide an effective impediment to tick movement into the yard.
There are two vaccines on the market for dogs to protect against Lyme Disease with the newer of the two being by far the safest (Recombitek Lyme vaccine by Merial). Interestingly however this same type of vaccine was taken off the market due to severe side effects in people. Once again are you willing to give your pet a vaccine that was deemed unsafe in people?
As you can see, the subject of Lyme Disease, it’s diagnosis, treatment, and prevention is a murky issue. Hopefully by being informed you will be able to make more thoughtful decisions regarding this issue for your pet.