Canine Lyme Disease

What is Lyme disease?

Lyme disease is a condition that causes fever, joint pain, lameness, and occasionally other symptoms in dogs. It is named after the towns of Lyme and Old Lyme, Connecticut, where the disease was first identified in people. (Note that the correct name of the condition is Lyme disease, after the place, not Lyme's disease, after a person.) Lyme disease is most common in the northeastern states, especially the New England area, but it is also found in other parts of the country.

What causes Lyme disease?

Lyme disease is caused by a microscopic organism called Borrelia burgdorferi. This organism is a spiral-shaped bacterium called a spirochete. The medical term for this condition is borreliosis.

These spirochetes are transmitted to the dog by ticks. When an infected tick bites the dog, the organisms are "injected" into the dog in the tick's saliva. The spirochetes enter the dog's bloodstream and are carried throughout the body. The membrane lining the joints is a common place for them to lodge and cause inflammation and tissue damage. Although very uncommon in dogs, the spirochetes can also invade the brain, heart muscle, and kidneys.

What are the signs of Lyme disease?

The signs of Lyme disease are rather vague. They often include loss of appetite, fever, and lameness, stiffness, or just vague signs of pain or discomfort. The lameness may develop suddenly and typically involves several joints. The dog may at first appear to be favoring or limping on one leg, only to be lame in another leg the next time you look. This pattern is called a "shifting" lameness. Sometimes the joint (or joints) most severely affected are swollen and painful to the touch.

Another common sign, although often not obvious just by looking at the dog, is swelling of the lymph nodes. These small nodules are an important part of the dog's immune system. They may become enlarged in response to infection and certain other disease processes. The more superficial lymph nodes can be felt in the throat area, just in front of the shoulder blade, and at the back of the thigh. Other signs, such as behavior changes, seizures, and heart rhythm disturbances, fortunately are rare.

Many dogs that are exposed to the organism never develop signs of Lyme disease. Apparently, they are able to rid themselves of the organism before it causes disease. In other dogs, it may take over a year before signs of infection become obvious.

How is Lyme disease diagnosed?

Lyme disease is often missed in the early stages because the signs are vague and several other conditions can cause similar symptoms. To complicate matters further, the signs may improve and even disappear without treatment, only to return weeks or months later.

In a dog with fever, lameness, and painful or swollen joints, your veterinarian may suspect Lyme disease on the basis of where the dog lives or a history of exposure to ticks. To make a definite diagnosis it is necessary to perform some laboratory tests. There are two types of test currently available for confirming Lyme disease in dogs:

1. Serology

This simple test determines the level of antibodies against the organism in the dog's blood. When the organisms enter the dog's bloodstream, the immune system begins producing antibodies against them. This antibody response can be measured; the result is often referred to as a titer. However, this test does not prove that the organism is present in the dog's body, just that the dog has been exposed to the organism at some time.

There are several situations in which this test may return a false-negative result: the organism is present in the body, yet the antibody titer is low or negative. The first is very recent exposure. If the test is performed within days of the dog's first exposure to the organism, before the body has had time to produce many antibodies against it, the test may be negative. The test may also be negative in a dog whose immune system is suppressed by illness or immunosuppressive drug therapy. In such a situation the dog may produce an inadequate antibody response to the organism. Similarly, a dog that has been infected for months or years may no longer be producing many antibodies. A positive result in a dog showing signs of Lyme disease is significant, but a negative result can be unreliable.

2. PCR (polymerase chain reaction)

This test identifies fragments of the organism's genetic material (DNA) in the dog's system. Unlike serology, PCR tests for the presence of the organism, not simply the body's immune response to it. PCR is a very sensitive test, detecting the presence of even a few organisms in the sample. It is also very specific for this spirochete, returning few false-positive results.

The test can be performed on blood and on joint fluid. Not all infected dogs have the organisms in their bloodstream for very long after exposure. So, fluid from an affected joint is usually the best sample to submit for PCR. Collecting a small sample of joint fluid is simple and relatively painless.

Can Lyme disease be treated?

Yes, very effectively if treatment is started early in the disease. Treatment involves antibiotic therapy, usually with a type of tetracycline or synthetic penicillin. While the dog may rapidly improve within days of beginning antibiotic therapy, it is necessary to continue treatment for several weeks to prevent relapse. Dogs that have had Lyme disease for weeks or months before treatment is begun usually respond to antibiotics much more slowly. Occasionally, it is necessary to change to another type of antibiotic in dogs that do not respond well to the first antibiotic used.

What can I do to prevent my dog from getting Lyme disease?

Protecting your dog from Lyme disease involves two aspects: preventing tick exposure and vaccination.

1. Preventing tick exposure
The spirochetes that cause Lyme disease are transmitted to the dog through the bite of an infected tick. Keeping your dog away from tick-infested areas and regularly applying insecticides that repel or kill ticks can decrease your dog's risk of exposure. Ticks are most likely to be found in tall grass and wooded areas with plenty of underbrush. So, try to keep your dog away from such areas during the warmer months of the year.

If your dog has been in a tick-infested area, check it immediately for ticks. If you find any ticks crawling in the dog's fur or on the skin, pick off the tick and crush it with your shoe or a rock. If you find a tick that is attached to the dog's skin, pull it off by grasping the tick as close to the dog's skin as possible and firmly pulling the tick straight out. Use your fingernails or a pair of tweezers to get as close to the dog's skin (and the tick's head) as possible when removing the tick.

It is important to check your dog right away after possible exposure and remove any ticks you find. The organism is not transmitted to the dog immediately the tick attaches; in fact, it may take up to 12 hours before the attached tick transmits the organisms to the dog. Once you've removed the tick, be careful not to get any of its contents on your skin when you crush it. Use your shoe or a rock to kill the tick, rather than your fingers. Humans are susceptible to Lyme disease, and the organism can enter your body through a cut or other break in the skin.

2. Vaccination

A safe and effective Lyme disease vaccine is now available for dogs. The initial vaccination course involves two injections, given two weeks apart. Thereafter, a yearly booster is needed to maintain protection. Your veterinarian may recommend this vaccine for all dogs that are likely to come into contact with ticks.

You mentioned that humans can get Lyme disease. Can I get if from my dog?

No, humans contract Lyme disease the same way dogs do: from the bite of an infected tick. So, protecting yourself and your family from Lyme disease involves the same procedures as discussed above for dogs. Avoid tick-infested areas or wear clothing that covers your skin, and check yourself for ticks after being in a tick-infested area. There is also a Lyme disease vaccine available for humans. Ask your physician about it.

Incidentally, one of the common early signs of Lyme disease in people is a rash at the site where the tick was attached. The rash develops within a few days, and up to a month, after exposure. The rash is characteristic and helps physicians diagnose Lyme disease early. (Dogs do not develop a rash, or if they do, it is missed because of their dense fur.)

by William M. Fraser, D.V.M.

petEncyclopedia | Contact Us