by Jennifer Chaitman, VMD, ACVIM (Internal Medicine)
Lyme disease is an illness caused by Borellia spirochetes, a tiny corkscrew shaped organism that lives in Ixodes ticks. In people, Lyme disease has been reported in 50 states, 85% of cases from the Eastern seaboard, from Virginia to Massachusetts, 10% from the upper Midwest, and 4% from California.
The tick must be attached for over a day for tick saliva to infect the host with the spirochete. Testing shows that 75% of dogs are exposed to Lyme in endemic areas but only 5 to 10% of dogs become sick with the disease. The reason that some dogs donít get sick could be that they were infected with a type of Borellia that doesnít cause illness or that they were infected with a low dose of Borellia and had healthy immune systems.
In experimentally infected dogs, illness occurs 2-6 months after exposure. Signs of illness include fever, shifting leg lameness, enlarged lymph nodes, decreased appetite, and lethargy. The arthritis usually presents as a polyarthritis, meaning that multiple limbs are affected. The organism can be found in the skin, connective, joint and muscle tissues. The first limb affected is usually closest to the site of tick attachment. Lameness will start in one limb, stay there a few days, then shift to another or disappear. Over time, it can cause a chronic arthritis that is not necessarily visible on x-rays.
Lyme can also cause kidney disease, including a protein losing nephropathy. This means that as the kidneys filter blood, valuable proteins that should stay in the body are lost into the urine. The kidneys can also lose their ability to filter out waste products and a build up of creatinine or blood urea nitrogen (uremia) can occur. In severe cases, the body can lose so much protein that edema results. Protein losing nephropathies are mostly seen in Labrador and Golden Retrievers. Clinical signs include vomiting, lethargy and weight loss.
Meningitis occurs in people but has not been recognized in dogs with Lyme.
Sometimes there is a small red lesion at the site of tick attachment but this is a different lesion than eryethma migrans, the bulls eye lesion seen in humans. Dogs do not form erythema migrans lesions from Lyme.
Cats may be more resistant than dogs to developing Lyme. In one study 13% of cats had positive blood tests for exposure but were not sicker than cats with negative results.
If you suspect that your dog has Lyme disease, you should ask your veterinarian to perform a physical exam and serologic or blood testing. Your veterinarian will need to make the conclusion whether your dog needs to be treated since a positive blood test does not necessarily mean that your dog has Lyme disease. If your dog has clinical signs of Lyme disease and has a quick response to an antibiotic appropriate for Lyme, it strongly suggests that illness is present. Antibodies to Lyme should be measured and if there is a rise in titer, it strongly suggests that an infection was present. Antibodies made soonest after infection are called IgM; antibodies made later are called IgG. IgG positive titers can be seen 4-6 weeks after exposure, are at their highest levels in three months, then can persist for over two years. If your dog has been vaccinated with a Lyme vaccine, your veterinarian will need to perform a special blood test called a western blot to determine if the positive titer is from exposure from a tick or from the vaccine.
Treatment includes an antibiotic for 3-4 weeks such as doxycycline.
The best prevention is avoidance. Remove ticks as soon as they are found and treat your dog with a preventic collar containing amitraz or topical solutions with selamectin (Revolution) or Frontline (fipronil). Permethrin is also an effective tick preventative.
In people, a single dose of doxycycline given at the time of tick attachment was 87% effective in preventing Lyme Borreliosis.
Vaccination against Lyme disease is still questionable. If given, it should be administered early in life, at 4 and 12 weeks of age. The vaccine will offer the best protection before the dog is ever bitten since antibodies must be present at the time the dog is bitten by a tick for Osp A vaccines. It also needs to be given once yearly since it doesnít last very long. It is usually reserved for outdoor dogs in endemic areas. There is some evidence that it may worsen kidney disease in dogs that have been vaccinated and then bit by a contaminated tick.