Your Pet and Lyme Disease

This information is not meant to be a substitute for veterinary care. Always follow the instructions provided by your veterinarian.

What is Lyme disease?

Lyme disease is caused by the corkscrew-shaped bacteria, Borrelia burgdorferi  which is also called a spirochete. The bacteria are carried by ticks which transmit the infection when they feed on animals and humans. The disease can cause generalized illness in animals and humans worldwide.


In the United States, Lyme disease occurs predominantly on the Pacific coast and in the Midwest, and Atlantic coast states. Regions in which the disease occurs commonly are called endemic regions. About 75% of dogs living in endemic regions are exposed to infected ticks, but only a small percentage of exposed dogs develop signs of disease.

Lyme disease was first described in 1975 when an unusual outbreak of rheumatoid arthritis occurring in children was reported in Lyme, Connecticut. In 1982, the bacteria Borrelia burgdorferi was determined to be the cause of that outbreak. Since Lyme disease was first described in the early 1980's, the frequency of occurrence of disease has increased twenty-five fold. Today, Lyme disease is the most common vector-borne (transmitted by insects or arthropods) disease occurring in people and probably in dogs in the United States. Dogs are most frequently infected with the Lyme disease bacteria, but infections can also occur in horses, cattle, and cats.

How is Lyme disease transmitted?

The bacteria live in mice, deer and other small mammals. The type of ticks that can transmit the bacteria from these wildlife to humans and domestic animals are the Ixodes ticks. The bacteria replicate (increase in number) in the wildlife without causing them to become sick. When a tick feeds on the infected wildlife the tick picks up the bacteria, then they transmit the bacteria to another animal the next time they feed.

If your pet is diagnosed with Lyme disease you are not at risk of getting Lyme disease directly from your pet. The bacteria increase to high levels in the blood of wildlife whereas humans and domestic animals develop very low levels of the bacteria in their blood and these low levels will not infect a feeding tick. Researchers have learned that infected ticks must feed for about 24 hours to transmit the bacteria to a susceptible animal so quick removal of ticks from your pet reduces the chance of infection.

Clinical signs

The most common sign of Lyme disease in dogs is arthritis, which causes sudden lameness, pain ands sometimes swelling in one or more joints. Other signs that may be seen include fever, lack of appetite, dehydration, inactivity, and swollen lymph nodes. In severe cases, the infection can cause kidney failure and death although this does not occur commonly in dogs. The signs of heart and nervous system dysfunction seen in infected humans are not often seen in animals.


Humans often show a skin rash that looks like a target but this is rarely seen in infected dogs.


A diagnosis of Lyme disease is usually made based upon a history of being in an endemic area, signs of arthritis and favorable response to treatment. There is a blood test that measures antibodies to the bacteria but many dogs that live in endemic regions will have a positive blood test. A positive blood test just means that the dog was exposed to Borrelia burgdorferi but not all dogs that are exposed will show signs of disease. Early in the disease dogs may not yet have a positive blood test. Dogs that have been vaccinated for Lyme disease may have a positive blood test depending upon the type of blood test that is performed. There are several other causes of arthritis that occur in dogs that must also be considered.


Borrelia burgdorferi is easily treated with antibiotics. The signs of Lyme disease usually regress rapidly in response to treatment. If the disease remains untreated the disease becomes chronic and can cause kidney damage although dogs are much less likely to develop chronic disease than are people.


Animals in endemic areas are at greatest risk for infection. The best method of prevention is to avoid tick infested areas, especially in the spring when the young ticks are most active. When returning from a tick-infested area do a thorough search for ticks on both yourself and your animals. Ticks should be removed carefully with a tweezers, pinching the tick near the point they enter the skin. There are also many highly effective veterinary products that will kill ticks on your dog before the tick can transmit the bacteria. Remember that early removal of ticks reduces the chance that the tick will transmit Lyme disease.

There is a vaccine approved for use in dogs for Lyme disease prevention. Most authors of veterinary articles on Lyme disease do not recommend vaccinating dogs in non-endemic areas. Not all authors agree on how effective the vaccine is in preventing Lyme disease and not all authors agree that the vaccine should be given in endemic regions. The vaccine can cause some blood tests for Lyme disease to become positive. For more information about tick control products or Lyme disease, consult your veterinarian.

For additional information on Lyme disease see: the Centers for Disease Control (CDC) website

This topic was written by Wendy Harless, Oregon State University, class of 2002 with the guidance of Dr. Diana Stone, Washington State University.

Washington State University assumes no liability for injury to you or your pet incurred by following these descriptions or procedures.

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