What is Borrelia Burgdorferi?
A Look at Lyme Disease, Its Causes and Prevention
Adapted, updated, and reproduced with permission from an article published in GWPCA Wire News, Health Forum, Autumn, 2013, by Karen Potter, DVM
Each year we are hearing more and more about Lyme disease in our canine patients. The first Lyme disease outbreak in the United States in humans was identified in Lyme, Connecticut in the 1970’s although reports of the disease can be traced back to Europe in the 1880’s. Lyme disease is an arthropod borne disease that uses ticks as a vector for transmission and is caused by the spirochete bacteria, Borrelia burgdorferi. Lyme disease was noted in dogs in the past decade, but the percentage of our canine companions that are testing seropositive for B. burgdorferi is drastically increasing. Infection with B. burgdorferi is common in the northeastern, upper midwestern, and West Coast states. In endemic areas, regional seroprevalence in dogs ranges from 1.4% in the West to as high as 13.3% in the Northeast.
View forecasts for Lyme Disease in your local area at https://petdiseasealerts.org.
The Bacteria and The Tick
B. burgdorferi is an aerobic, gram negative spirochete bacteria that causes the condition that we know as Lyme disease. The bacterium is most commonly transmitted by Ixodes scapularis and Ixodes pacificus, also known as the eastern and western black-legged ticks. It is believed that there are a couple other Ixodes spp. that can potentially carry the disease, however it is much less common and it is unknown whether these ticks feed on people or pets. The carrier ticks inoculate pets and people with B. burgdorferi while they are feeding. Ixodes spp. have a two year life cycle with 3 stages, the larva, nymph and adult
Larva: This is the first stage after hatching. The larvae attach and feed on small animals and rodents. They are most active late summer and fall. The larval stage is when ticks are most likely to acquire B. burgdorferi.
Nymph: The second stage of the life cycle that is most active in the spring and summer months. This stage attaches to small and medium mammals and is when most transmission of B. burgdorferi occurs.
Adult: The final, adult stage most commonly attaches to deer. They are most active in the cooler months of the fall. The adult female will then lay eggs in the spring that that will hatch into larvae.
There has not been any evidence that adult ticks can pass B. burgdorferi onto their offspring. This implies that the only method of the ticks acquiring the bacteria is from the larvae or nymphs feeding on the reservoir hosts (small mammals and rodents). In order for the nymphs or adults to transmit B. burgdorferi they must be attached for 24 to 48 hours. This is the time it requires for the bacteria to pass across the salivary glands of the ticks and into our pets or us.
Although experimentally infected dogs have been shown capable of infecting ticks and thus theoretically could serve as a reservoir host of B. burgdorferi, dogs are not considered an important source of human infection due to the feeding behaviors of I. scapularis and I. pacificus.
Clinical Canine Lyme Disease
Clinical presentation of Lyme disease is seen in a very low percentage of dogs that test seropositive. Some studies have even shown that less than 5% of dogs that test positive will manifest with clinical signs. These clinical signs typically begin 1 to 5 months after the tick bite that inoculated the dog with B. burgdorferi. Younger dogs seem to be more likely to have Lyme disease. This may be due to the activities that younger dogs participate in , where as older canines are a bit more sedate.
Dogs with Acute Lyme disease may present with shifting leg lameness, swollen joints, regional lymph node enlargement and potentially fever, lethargy, depression and anorexia. The joints affected are normally the carpus or the tarsus (the “wrists” and hock joints, respectively). The lameness may last for 3 to 6 days in one joint before subsiding and potentially targeting a different joint in a few days. This is where the description of “shifting leg lameness” comes from. Chronic Lyme disease is less common in dogs than the acute form. This form is characterized by shifting leg lameness leading to a condition called polyarthritis (inflammation in multiple joints). In Chronic Lyme disease, polyarthritis may persist even with antibiotic therapy. It is rare, however, this may lead to kidney failure, heart problems and neurologic conditions.
Diagnosis
With the high percentage of dogs that are seropositive for B. burgdorferi that do not have clinical Lyme disease, care must be taken evaluating the clinical presentation of a dog along with test results. Screening tests that are performed in the veterinary clinic, such as the Idexx 4Dx Snap Test, can be beneficial to identify dogs that are testing seropositive. A positive test, however, only indicates exposure to B. burgdorferi. It does not necessarily mean the dog has Lyme disease. On the other hand, with dogs that are presenting with clinical signs suggestive of Lyme disease, the immediate positive result of these tests can more quickly identify a definitive diagnosis, making treatment decisions quicker and more effective. Other serological testing, such as titer testing can be sent to outside laboratories. These tests are very beneficial but the results will be delayed for a couple days. Skin culture for spirochete bacteria and PCR of the skin are considered most definitive and sensitive, however, these tests are not commonly done in practice.
Treatment
The first treatment choice for acute Lyme disease is the antibiotic, Doxycycline, 10mg/kg, every 24 hours for up to 30 days. Other tetracyclines and penicillin type antibiotics are also successful in treating the disease. In regards to treating Chronic Lyme disease, these dogs may require long term antibiotic and pain therapy along with kidney support. This chronic state may never be cleared.
Prevention
Number one prevention is prevention of ticks. Most tick preventatives are focused on killing the tick prior to the 24 to 48 hours of attachment time that is required to transmit disease. Although you may be using a tick preventative, daily tick checks of your dogs is another line of defense you can provide. Please remember that although you have a tick preventative on your dog, this does not mean that you will never find a tick. The ticks must be on your dog before they can be killed by the preventative. Check for ticks all over the body, but primarily they will be in the ears, groin and armpits. If a tick is found, grasp the tick as close to the skin as possible with hemostats or tweezers and remove. It is very common for a small piece of skin to come along with the tick that you remove.
Vaccines are available for Lyme disease. The efficacy of these vaccines has been questioned, however, for a dog that lives in a high-risk area they should be considered. Vaccination of your dog does not replace good tick prevention and daily tick checks.
Lyme disease is a true threat and even more to our hunting dog companions. Our dogs are more commonly in the woods and fields and therefore more exposed to those nasty little ticks that carry B. burgdorferi.
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