Lyme Disease in Dogs and Horses

Lyme disease is caused by the bacteria Borrelia burgdorferi, which can be transmitted by ticks to both animals and humans. First recognized in 1975, Lyme disease has become an increasingly common problem and is now the most common tick-borne illness in the United States. Lyme disease is most prevalent in the Northeast and Midwest. While it is estimated that a very high percentage of dogs and horses in these regions are exposed to ticks, they do not all develop the illness. Still, Lyme disease is on the rise. Other animals that can become infected include deer, horses, cattle, cats (rarely) and mice.

Transmission of Lyme Disease

The ticks that transmit Lyme disease are known as deer ticks or blacklegged ticks. When they feed on infected animals in the wild, commonly deer and mice, and then feed on a domesticated animal or human, the disease is transmitted. Research has shown that a tick must be attached to an animal for at least 36 to 48 hours in order to transmit the disease. There is no chance of direct transmission of the illness from an animal to its owner or handler.

Symptoms of Lyme Disease

Ticks are less visible on animals, particularly those with dark coats, than they are on humans, and animals do not usually develop an observable bull's-eye rash. Symptoms of Lyme disease usually show up earlier in dogs than in horses, and while some of the symptoms are the same, dogs are more likely to experience the disease's early flu-like symptoms, which include fever, lethargy, loss of appetite and swollen lymph nodes. Both dogs and horses, if infected with Lyme disease, may show the following symptoms weeks or even months after the tick bite:

Lameness, especially "shifting leg" lameness
Swollen joints (arthritis)
Pain upon being touched

While the most frequently reported symptom of Lyme disease in horses is arthritis, horses are also apt to develop symptoms, such as eye disease, dermatitis and neurological complications, not common in dogs.

Diagnosis of Lyme Disease

Lyme disease is more commonly suspected in dogs with arthritic symptoms than in horses with the same symptoms. This is because swollen joints and lameness are more prevalent in horses and may result from a variety of causes, and because horses develop symptoms from Lyme disease more rarely than dogs do. In dogs (particularly those allowed to run free) living in regions where the illness is endemic, Lyme disease is usually suspected at once. With horses, Lyme disease is not usually suspected until other more typical causes of lameness have been ruled out.

The blood tests for Lyme disease are not foolproof, because animals living in regions where Lyme disease is prevalent will test positive for its antibodies. Moreover, if a dog has been vaccinated for Lyme disease, it may also test positive. Recently, a blood test has become available that may give a clearer picture of whether the animal has an active case of Lyme disease, but in many cases diagnosis is confirmed by treatment. If administration of the appropriate medication relieves an animal's symptoms, it is viewed as confirmation that the animal was infected with the disease.

Treatment of Lyme Disease

Lyme disease in dogs and horses is effectively treated with doxycycline, an antibiotic with anti-inflammatory properties. In dogs, symptoms generally abate rapidly and completely. Dogs are much less likely to develop a chronic variety of Lyme disease than humans. Unfortunately, horses, although they become ill with the disease more rarely than dogs, more frequently develop its chronic form.

Prevention of Lyme Disease

There is an vaccine available to prevent Lyme disease in dogs that the majority of veterinarians prescribe, particularly in regions where the illness is endemic. There is no such vaccine available for horses, though research and testing are being done to find one. In the meantime, a great many equine veterinarians are administering the dog vaccine to horses because it seems to offer some short-term protection against the disease.

Other methods of preventing Lyme disease in dogs and horses include:

Keeping the animals in general good health
Checking the animals regularly for ticks
Removing any discovered ticks immediately
Using tick repellents
Having the animals checked regularly by veterinarians