What is it? Lyme disease is caused by Borrelia burgdorferi spirochete.
How is it spread? The main carrier is the Ixodes scapularis tick, aka the deer tick.
What are the clinical signs of Lyme disease? 95% of dogs are asymptomatic. In the acute form, dogs can have a transient fever, anorexia, depression and a shifting lameness. The joints closest to the tick-bite are affected first. The chronic disease seen in man does not occur in dogs. The superficial lymph nodes closest to the tick bite may be enlarged. Rarely Lyme nephritis occurs and is usually fatal. This form is more common in Shetland Sheepdogs, Labs, and Goldens.
Incubation of the disease is 2-5months so they may take a while to develop clinical signs.
About the tick: In the spring (once it is >4 degrees Celsius) the tick becomes active and the female tick lays a cluster of about 2000 eggs. The 6-legged larva hatches from the egg and searches for a host. Since the larva is small it typically attaches to a small host like the white-footed mouse. If the mouse is carrying the Lyme disease spirochete the larva becomes infected at this point. The larva feeds until it is full of blood and then drops off and is dormant approximately 1 year until the following spring. The next spring, the larva molts and becomes a nymph. The nymph is larger than the larva and therefore can select a larger host but may still select another mouse. This nymph feeds for 3-5 days and then falls off and is dormant but this time only until late summer. In the late summer, it molts into an adult tick. This adult tick looks for a larger host, like a deer, dog or human. These adult ticks mate on their new host, feed and transmit the Lyme spirochete if they are carrying it. This larger tick has to keep the host’s blood from clotting so it regurgitates enzymes to keep the blood flowing. It is only during this phase that they can transfer Lyme disease to their host.
How long does it take to transfer Lyme disease? This process can take 24 – 48 hours, so if a tick is removed prior to feeding for this period, the spirochete cannot be transmitted to the host.
My dog has a tick!! When an owner calls or comes in with a tick on their dog the discussion of performing a 4DX test is had. This tick, if small, likely hasn’t transferred Lyme disease but now we know that the dog has been or lives in a tick area and this is likely not its first tick and still, should have a 4Dx test at the appropriate time after discussing with you veterinarian. IF the tick is large, it likely has fed long enough to transfer Lyme disease and should have the test done 6 weeks after the tick has been removed. Depending on when the dog was exposed it may or may not have symptoms of Lyme disease yet.
Lyme positive on 4DX, now what? The best medicine is to recommend running a QC6 test at the Idexx laboratory. This tests the antibody level (quantitative) against the C6 peptide (a unique surface antigen). This gives an exact antibody number. The vaccine does not contain this peptide so vaccines will not affect this level. If treatment is needed we then have a way to monitor response to treatment. Some people cannot afford this test and so, if symptomatic, we proceed with treatment. This test should not be run until 6 weeks after a tick bite, even if you have a positive snap test.
Products? We are all on board for using Nexgard and Heartgard in combination for most cases this year. Some pets have received other products in the past and we can still use/order these products after a discussion of product do’s and dont’s. For example, Advantix users should be questioned at the time of product dispensing–do you have a cat, are you pregnant/nursing, have young kids, immunosuppressed?? If owner’s answer yes to any of these questions this is not the product for them. For any further questions or have concerns with your pet regarding ticks and the diseases they carry please contact our office.
Written by Dr. Ashley Kirkham