Compiled from materials provided by Steven A. Levy, VMD, Durham Veterinary Hospital, Durham, Connecticut
In recent years, ticks have become much more than just disgusting nuisances for dog owners as we have learned that they can carry and transmit a variety of diseases to our dogs. Perhaps the best known tick-borne illness is Lyme Disease. The first outbreak of Lyme Disease in humans occurred in Old Lyme, Connecticut in 1975. The first case of canine Lyme arthritis was reported in 1984. Since that time cardiac (heart) and renal (kidney) effects of Lyme have also been noted. Lyme has been reported in humans in 47 of the lower 48 states and is endemic (always present) on the east coast, west coast and upper Midwest.
The organism (pathogen) that causes Lyme Disease is a spiral shaped bacteria (spirochete) called Borrelia burgdorferi. Ticks are the vectors that transmit the pathogen Borrelia burgdorferi from a reservoir host animal to a non-infected animal. Lyme disease is vectored by two kinds of ticks: Ixodes scapularis on the mid Atlantic coast, northeast New England and upper Midwest and Ixodes pacificus on the west coast and in British Columbia. These ticks may be active from September through July depending on weather conditions and geographic location.
Ixodes scapularis ticks feed on three different hosts during their development from eggs to adult ticks. Eggs hatch and larvae feed on small mammals, such as rodents, which may be carriers of the Lyme organism. In regions where winters are cold, it takes two years for ticks to mature which is ideal for the maintenance of infection. When tick larvae infected by feeding on rodents in the fall molt to nymphs the next spring, the next generation of rodents can be infected. And the cycle continues.
Ixodes ticks live up to two years and that longevity perpetuates the pathogen within the tick. The pathogens taken in the tick's blood meal escape the tick's digestive process when they are internalized by the cells which line the tick's digestive tract. Ixodes ticks can produce up to 22,000 eggs in one egg clutch and Ixodes scapularis and pacificus females generally lay up to several thousand eggs before they die. Ticks have the ability through their saliva to suppress an immune response in the host, thus allowing repeat feedings on the same host by many ticks.
Borrelia burgdorferi is transmitted to a host via tick saliva after a lag phase of approximately 24 to 48 hours. In mammals, the bacteria takes up residence in the layer of cells that line the inside of blood vessels and may lie dormant in connective tissue. It is difficult to detect the bacteria in blood or in tissue and the bacteria can evade both the host's immune response and antibiotic therapy. It takes three to six weeks for the production of antibodies which indicate that an animal has been infected by the organism. This is important because the best way to test for infection is to test for antibodies.
The incubation period for the disease in naturally infected dogs is unknown but in laboratory dogs clinical signs develop from two to five months after exposure to infected ticks.
Clinical signs of Lyme disease include inflammation of the joints (arthritis), the heart (carditis) or the kidneys (nephritis/renal) and nervous system abnormalities. Lyme arthritis is characterized by sudden onset of joint swelling, lameness, fever and lethargy and swollen lymph nodes, while some dogs may show more chronic and less dramatic signs. Cardiac Lyme is characterized by heart block and treatment must include a pacemaker and antibiotics. Renal Lyme is generally fatal (kidney failure) and often occurs in young adult dogs. Central nervous system infection with Lyme has been associated with seizure disorders.
One of the most confusing issues in the diagnosis of Lyme disease has been the significance of testing. A test result that shows antibodies directed against Borrelia burgdorferi is merely an indication of exposure to the organism or to a vaccine (which contains an antigen). A positive test result by itself does not constitute a diagnosis of Lyme disease.
Recently a new test has been developed to aid in the diagnosis of canine Lyme
Disease. Antibodies to Borrelia burgdorferi detected by previously available
tests could not be identified as either infection or vaccination induced
antibodies without performing an expensive test called a Western blot. The new
test is called a C6 ELISA and is available in the SNAP3Dx test kit which
provides the veterinarian with data concerning three vector borne diseases of
dogs: Heartworm, canine Erlichiosis and Lyme disease. The C6 ELISA component of
the SNAP3Dx is unique in that it is specific for the antibody that is produced
when live Borrelia burgdorferi interact with cells in the spleen of an infected
animal. Thus it offers the veterinarian the ability to determine whether a dog
has Borrelia burgdorferi antibody that is produced in response to active
infection rather than by vaccination.
Tick avoidance, control and tick bite prevention. Keep dogs out of areas with tall grass, etc. Ticks wait on grass and leaves and can detect a dog's presence by smelling carbon dioxide (on a mammal's breath), or other odorants produced by the dog. When a dog (or other mammal) contacts the tick by brushing against the vegetation where the tick is waiting, the tick transfers to that animal, grasps securely with claws on the ends of its legs and then finds a place to make a small incision and attach itself by secreting a glue-like substance. Conduct careful tick checks every time a dog has been outdoors.
Products that are put on the host (dog) can produce good results in tick control. The Preventic collar is the only tick control product with a study to prove that it can prevent disease transmission. Frontline, a spot-on insecticide containing fipronil, kills ticks that contact it within 24-48 hours. Therefore, it is possible that an infected tick could transmit the disease to the dog before the fipronil killed the tick.
A 1993 published study of dogs immunized with LymeVax indicated that vaccinating before tick-borne exposure gives the best protection against Lyme disease. Immunization with LymeVax has been demonstrated to be safe - even for dogs already infected with Borrelia burgdorferi. However, it is important to note that even if they are immunized with LymeVax, dogs with positive C6 antibody tests are already infected and might still develop the disease due to the prior infection.
Vaccinating young pups in endemic areas as part of the routine puppy series - before they have been bitten by infected ticks - is the best way to protect them.
Dogs with signs of Lyme arthritis and positive SNAP/C6 tests should be started on antibiotic protocols for up to 28 days. The dog's response to the antibiotics should be rechecked in 14 days and if a favorable response is noted, a LymeVax vaccination series should be initiated. If the response to the antibiotics is minimal or the symptoms have worsened, the veterinarian should reassess the diagnosis.
In endemic areas, any dog older than a puppy should be considered at risk for prior exposure. Adult dogs should be given the SNAP test to determine if the dog has been infected with the disease. Adult dogs without clinical signs should be tested with SNAP and immunized with LymeVax as soon as they move to endemic areas. Dogs with positive C6 tests can be started on antibiotic protocols concurrent with the first dose of LymeVax. A second vaccination is given two weeks later. The vaccinations are given annually thereafter.
Questions have been raised about signs of Lyme disease arising after the dog has been vaccinated. However, no data or hard evidence has proved the possible post-immunization syndrome. Dr. Levy has vaccinated more than 1000 dogs annually with LymeVax since 1990 and has not observed a post-vaccination syndrome in any of them. Dogs given Lyme vaccines may experience the same post-vaccination discomfort seen with any of the vaccines which are administered to dogs. The 1993 study demonstrated that LymeVax was both safe and effective in un-infected dogs as well as dogs which had already been bitten by infected ticks.
Lyme arthritis is a crippling and painful condition for a dog to suffer but it is an obvious symptom of Lyme disease so you know something is wrong and you can treat it. (Nonetheless, 15-25% of dogs treated for Lyme arthritis will become chronically affected and have incomplete resolution of signs or recurrent disease.)
Since Lyme disease can also invisibly affect the heart, kidneys and nervous system without the dog showing clinical signs until it is too late, it is essential to try to protect your dog from the disease. If you live in an area where the disease is present (check with your veterinarian), consider the protocol outlined above. Encourage your veterinarian to use the SNAP test as a way to determine what the incidence of Lyme disease in your area is.
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