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May 2006

Lyme Disease (Borreliosis)
Veterinary & Aquatic Services Department, Drs. Foster & Smith, Inc.

Copyright © 1997-2006, Foster & Smith, Inc. All Rights Reserved.
Reprinted from PetEducation.com with permission.




Lyme disease (borreliosis) is an infectious, tick-borne disease first recognized in dogs in 1984. It is caused by Borrelia burgdorferi, a type of bacteria called a 'spirochete.' The common deer tick Ixodes scapularis (formerly called Ixodes dammini) is the primary carrier of B. burgdorferi in the Northeast and upper Midwest. The tick Ixodes pacificus is the primary carrier in the West.

Although the disease in Connecticut was first diagnosed in 1975, there is evidence that it has existed in wildlife for many years. Tissue samples taken from a white-footed mouse in Massachusetts in 1894 that have recently undergone DNA testing show that it was infected with Lyme disease. Certain environmental factors have caused Lyme disease to be more prevalent in people in the twentieth century. Before 1900, the habitat in the East and upper Midwest was heavily deforested by early settlers. Deer and their associated ticks were greatly reduced. The reforestation of these areas and the resulting booming white-tailed deer population in these areas are probably a big factor in the increase in the incidence. This coupled with increased awareness and testing capabilities has led to the greatly increased reporting of the disease.

Where is Lyme disease found?

Prevalence of Lyme Disease in the U.S.

Despite the fact that people and dogs from all states have been infected with the disease, it is felt that they acquired the disease by traveling to endemic areas. Only a relatively small portion of the United States is endemic for the disease. However, all of the areas where Lyme disease is present are areas with high human and pet populations bringing the total number of people and animals that can be potentially exposed to a high number. In humans, 85% of cases have occurred in the eastern coastal states from Massachusetts to Virginia. 10% of the cases come from Wisconsin and Minnesota and 4% from California. All of the other states account for less than 1% of the disease. Contrary to some media reports, Lyme disease is not spreading in epidemic proportions and is likely being over diagnosed by those using serologic (blood) testing.


Life cycle of the deer tick

The deer tick (I. scapularis) goes through several stages in its life cycle. In the spring, the eggs hatch into larvae. During the summer, the larvae then bite a previously infected white-footed mouse. This infected larva will then winter over until the following spring when it becomes a nymph. The infected nymph then bites another mouse, or it bites a deer, dog, or human infecting them. The nymph then molts into an adult and lays its eggs, which will hatch the following spring.



For a nymph to transmit B. burgdorferi, it must be attached to the host for at least 48 hours. If a tick dies or is removed within this 48-hour period, transmission of the bacteria will not occur. Even if a tick is a carrier of B. burgdorferi and it attaches to the dog for more than 48 hours, the dog may not contract the disease. In fact, studies show that only around 10% of dogs that are exposed will contract the disease. There is no evidence to suggest that infected dogs pose a risk to other members of the household except as a reservoir of infected ticks. Once a tick has had a full meal, it will detach and not bite another mammal. The risk comes from ticks that have not gotten a complete meal and are detached. They could possibly seek out a human and bite them causing infection. Other types of ticks and insects have been shown to be infected with B. burgdorferi, but they are considered insignificant spreaders of the disease.



Clinical illness usually occurs 2 to 5 months after initial exposure and the likelihood of disease and the severity of the disease seems to vary with the animal's age and immune status. Cats can develop Lyme disease, but it occurs rarely in them, even in endemic areas. Other domestic animals such as horses have contracted Lyme disease, but it does not appear to be a significant problem. Dogs show several different forms of the disease, but by far, the most common symptoms are a fever of between 103 and 105°, shifting leg lameness, swelling in the joints, lethargy, inappetence, and maybe most importantly, response to appropriate antibiotics.

Arthritis may be a result of both short- and long-term infections. Most dogs that are promptly diagnosed and treated do not appear to develop arthritis, but a few dogs who do not respond completely to treatment or were not treated will develop progressive degeneration of the infected joints.

A few dogs have developed severe progressive renal disease as sequelae to Lyme disease. This severe kidney failure is non-responsive to treatment and death is often the outcome. Fortunately, this form appears to be rare.

Usually, dogs will not develop any rash or the circular area of redness around the bite (erythema migrans) which is seen in people.


Ten years ago, Lyme disease was often under-diagnosed, but today, the opposite is true. Because of the lack of sensitivity of the blood test, many dogs show positive test results, but are not actually infected with the disease. The standard blood test detects antibodies made by the dog in response to infection with B. burgdorferi. The problem is that many animals are exposed to the organism, but fight the infection off on their own. These animals will have antibodies to B. burgdorferi but not have the disease. As we mentioned earlier, only around 10% of the exposed dogs actually contract the infection. At the same time the antibody test cannot distinguish between a dog that has been vaccinated or naturally exposed to Borrelia. Therefore, in endemic areas, the test alone is not an accurate way to get a diagnosis. However, the test can be used with several other criteria to gain a positive diagnosis. Suspected animals should have a history of tick exposure, compatible clinical signs, and have a rapid response to antibiotic therapy. In fact, clinical signs and rapid response to doxycycline antibiotic therapy is how I make a diagnosis of Lyme disease. A practitioner in a Lyme endemic area will often be able to diagnose the disease on physical exam. Practitioners in areas that have fewer Lyme cases may have to resort to using the blood test and treatment to confirm the diagnosis. If an animal that is suspected of having Lyme disease does not clinically improve within 48 hours of starting antibiotic therapy, assume that it is not Lyme disease and begin to do other diagnostic tests to find the source of the problem.



Treatment for Lyme disease is very straightforward and consists of using either a tetracycline or penicillin-based antibiotic. The two most commonly used are oral Doxycycline or Amoxicillin. A recent study showed that both antibiotics worked equally well. The antibiotics must be given a minimum of 14 days, but 30 days is recommended. However, some preliminary studies show that some animals may not even clear the organism after 30 days and will relapse once the antibiotic is discontinued. In these cases, the animal may have to be on the antibiotic for much longer. It appears that some animals may never completely rid themselves of B. burgdorferi despite aggressive treatment. These animals may suffer from increased degenerative changes in the joints leading to premature arthritis. Despite the fact that some animals may develop chronic infections, the vast majority of infected dogs respond rapidly and satisfactorily to doxycycline treatment. In some animals with severe arthritis, pain killers such as buffered aspirin (Do NOT give your cat aspirin unless prescribed by your veterinarian.) can also be used in addition to antibiotics. The use of steroids in this disease is definitely contraindicated.


Tick control is the best way to prevent Lyme disease.

Prevention of Lyme disease involves the use of vaccination and tick control programs.

Vaccination: There are several whole-cell killed vaccines on the market that are licensed for use in the dog, but total protection of a dog through vaccination is difficult. One reason is that a strain of Borrelia bacteria can mutate into a different strain. Unfortunately, antibodies made in response to one strain of the bacteria will not always be able to kill a different strain. In addition, if an animal is previously infected with the disease the vaccine will not offer any protection. These facts coupled with the relatively long incubation period (up to 5 months) contribute to the failure of some of these vaccines in preventing disease.

Some veterinarians have criticized the ineffectiveness of the Lyme vaccines and do not recommend their use. Although many dogs have been vaccinated and treated for Lyme disease, some vaccinated animals contract the disease, but it appears that vaccinated animals are less likely to contract the disease than unvaccinated animals. Vaccinations can be started after 12 weeks of age and it is recommended that two doses be given three weeks apart, then boostered yearly after that. Because of the inherent problems of over-vaccination, it is recommended that only dogs that are exposed to ticks in areas where Lyme disease is a problem be vaccinated.

Tick Control: Tick control is probably the most important thing an owner can do to prevent Lyme disease in their pet. Ticks carry many other diseases besides Lyme disease and by preventing them from attaching to your pet, we can prevent all of these diseases. Avoiding areas of high tick infestation during periods when ticks are active is one of the best ways to avoid contact.

Using insecticides on the dog that repel ticks is another method. With the advent of once-a-month topical insecticides containing permethrin, tick control has become a lot easier and more effective. Permethrin, which is an ingredient in Bio Spot for Dogs, is a very good repellent, and if the tick attaches itself to the animal it will die within 12 hours preventing the passage of the B. burgdorferi. (Permethrins should NOT be used on cats.) Very few tick collars are effective with the exception of a newer collar that contains Amitraz. Amitraz is an organophosphate that is very effective at repelling and killing ticks, but has little effect on fleas. Often using Bio Spot along with a Preventic Collar gives the best protection. Despite the claims made by many products to be effective against ticks, do not be fooled. Ticks are very tough and hard to kill. Our customers indicate that they have had the best luck with the products containing permethrin, fipronil, or amitraz.

Removing a Tick: If you find a tick on your dog, do not panic. Check out our article How do I Safely Remove a Tick? Ticks carrying Lyme disease are very small and most people never see them.


The tick-borne spirochete Borrelia burgdorferi causes Lyme disease. It often creates symptoms of lameness and fever. It is very treatable with antibiotics. There are vaccines available for dogs. The human Lyme disease vaccine has been discontinued. Preventing tick attachment is one of the best ways to control the disease.

Click here for information on the Human Lyme Testing.


      Greene, C. Infectious Diseases of the Dog and Cat. W.B. Saunders Co. Philadelphia, PA; 1998.

      Levy. "Veterinarians still faced with difficulty in diagnosing Lyme disease." DVM Magazine.            

Related Articles:

o       Human Lyme Disease Vaccine

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