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My dog just tested positive for Lyme, what does this mean?

Written by Heather Norton-Bower, DVM.

Canine Lyme disease is a complicated and often confusing disease. Here are the answers to many commonly encountered questions about Lyme disease and some explanations for our current recommendations surrounding yearly Lyme vaccination, seasonal tick control products, and Lyme testing.

What causes Lyme disease?  

Lyme disease is transmitted by the bite of a tick infected with a spirochete bacteria called Borrelia burgdorferi.  Here in Minnesota, the tick that transmits Lyme disease is Ixodes scapularis, more commonly known as the "deer tick."  The deer tick has three life stages (larvae, nymph, and adult) within a 2 year life cycle.  Humans and pets are usually infected by nymphs (that normally feed on rodents and small mammals) or adult ticks (that feed on deer and other larger mammals).  The Lyme hotspots in MN are typically central MN and the MN/WI border.

How does Lyme disease differ in humans and in dogs?

Over 90% of infected humans will show clinical signs of Lyme disease.  The initial signs of Lyme disease in humans are often the classic bull's eye lesion (erythema migrans) and flu-like symptoms.  Unlike their human owners, clinical signs of Lyme disease are observed only in approximately 5-15% of infected canine cases.  When early clinical signs occur, they typically occur about 2 months after the infection.  Signs include lameness (limping or abnormal walking/running behavior), arthritis in one or multiple joints, enlarged lymph nodes, lethargy (weakness), and fever.  Skin lesions are very rare in dogs.

How common is Lyme infection in dogs?

The true prevalence of Lyme infections in dogs is unknown, but informal surveys and anecdotal reports from veterinary clinicians practicing in hot-spot Lyme areas indicate that between 10-60% of dogs not vaccinated for Lyme may test positive for Borrelia burgdorferi.

How is canine Lyme disease treated?

The clinical signs of Lyme disease are treated with antibiotics, and often the symptoms will resolve within 3 days of therapy.  A tetracycline antibiotic called doxycycline is the most common antibiotic that is used to treat Lyme disease.  It is often chosen over other potentially effective antibiotics because it is likely to be better at treating additional bacteria that may have co-infected the pet (it is thought in hot-spot Lyme areas that 50% of ticks that are infected with Lyme bacteria are also infected with another worrisome bacteria called Anaplasma phagocicytophilium (formerly called Ehrlichia equi).

How does Westgate test for Lyme disease?

Because the majority of canine Lyme infections are asymptomatic, we believe in routinely testing a pet's Lyme status each year at heartworm testing time.  Antibodies that are formed by the pet's immune system when the tick infects the pet cause the positive "dot" we see on our in-clinic 4DX Snap test made by Idexx Laboratories (this is also combined with a heartworm, Ehlichia, and Anaplasma test).  A positive does not indicate that there is an "active" Lyme infection, only that the pet was exposed/infected in the past. With a darker dot, we are more inclined to think that the infection/exposure is more recent.  With a lighter dot, we are more inclined to think that the infection is less recent.  Previous vaccination for Lyme disease does not interfere with these test results (a vaccinated dog will not be positive for Lyme simply because it has received the Lyme vaccine in the past).  It takes a few weeks from the time of exposure for the development of a positive antibody Lyme test.

Why should my dog that is showing no symptoms of Lyme disease be treated?

Many dogs that are positive for antibodies against Lyme infection never develop any clinical symptoms (remember only about 10% show obvious signs).  There are several reasons that we recommend treatment for any dog that tests positive for Lyme infection:

1) The antibiotics used are usually easily administered and rarely cause any negative side effects.  When side effects are encountered they can often be solved easily by changing dosage or frequency of administration.

2) If your pet shows a positive for Lyme infection, it may be that the test is positive before clinical signs have developed.  Treating before the pet shows clinical symptoms allows us to treat more effectively.

3) The most important reason in my mind for treating a non-clinical Lyme positive dog is that some positive dogs will go on to develop chronic problems months or even years later.  Chronic problems from Lyme disease may include kidney, heart, or neurologic problems.  In dogs, the most common of these chronic problems is possibly irreversible kidney failure (a form called glomerulonephritis).  Kidney failure can ultimately reduce a pet's quality of life and lifespan.  Golden and Labrador Retrievers are breeds that are possibly more predisposed to this chronic problem.

Is therapy 100% effective?

Unfortunately, the answer is likely no.  Some dogs that are treated with months or even years of doxycycline still show positive antibody levels in the future.  Despite treatment, the infection can "hide" out in the body for years and always has the potential to cause future problems.  Newer evidence shows, however, that treatment with antibiotics, especially closer to the time of infection, may lower the antibody levels faster than they would fall without treatment.  Recent preliminary evidence indicates that lowering the antibody levels may reduce the risk of developing kidney failure in the future.

What additional testing may be done for my pet if they test positive for Lyme infection?

A urinalysis is usually recommended because the first sign of a potential kidney problem due to Lyme disease in dogs is the presence of protein in the urine that can't be attributed to other issues.  Depending on the results, other tests may be indicated.

How do I prevent Lyme infections to my pet?

1) Tick Removal.

It takes time for an infected deer tick to transmit Lyme bacteria to a pet.  Normally infection will not happen any sooner than 48-72 hours from the beginning of a blood meal.  While daily tick removal would theoretically be the best at reducing risk of Lyme disease, this is very impractical in most dogs, especially the furrier breeds, as most stages of the deer tick are so small that we wouldn't even notice them on our own skin.  (If you do find ticks on your pet, it is always advised to use gloves during removal as there is some potential for transmission to you from the tick.)
2) Application of a tick control product.

Since the highly infective nymph stages of tick can transmit the disease after only about 5 warm days in the spring and infections can extend through the fall into the winter, we recommend applying a tick prevention product once monthly from March through November.  The product that we most highly recommend currently is Frontline Plus Topspot.  This product is also effective in preventing or treating flea problems.  In recent studies, Frontline was 97.6 to 100% effective in reducing attached ticks.  Although we especially recommend topical prevention if your pet will be visiting hot-spot Lyme areas, topical prevention is important even if your pet lives in an urban area such as Minneapolis or St. Paul because one of the highly infective tick stages (the nymph stage) typically feeds on rodents and small mammals and these can live anywhere.  Lastly, use of a tick control product does more than help prevent Lyme.  It helps prevent other tick-borne diseases such as Ehrlichiosis, Anaplasmosis, and Babesiosis.

3) Vaccination for Lyme disease.

We have a highly effective Lyme vaccine that can be given to pets 9 weeks and older.  Although some studies indicate our Lyme vaccine is nearly 100% efficacious, we also recommend using a tick prevention product as outlined above.  Used together, we think this is the best way to protect your pet from Lyme infections and disease.   

If my dog is Lyme positive, should it still be vaccinated for Lyme disease in the future?

A recent talk that many of us attended recommended vaccination of healthy Lyme positive dogs in the future so that we can lower the risk of additional future infections.  Studies of the bacteria that transmit Lyme disease seem to indicate that one infection does not automatically provide your pet with immunity against the next infection. This has been a controversial topic in the veterinary community.

If my pet is infected with Lyme, am I or my family at risk?

You are not directly at risk of getting Lyme disease from your pet.  What a positive Lyme test in your pet indicates, however, is that you are at risk of encountering the same ticks that transmitted the infection to your dog.

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