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My dog's Lyme test came back positive! What does that mean?

Lyme disease is spread by ticks, and the ticks are out in Minnesota!  Ticks live for many years, and can survive the winter in a dormant stage.  Ticks become active when the ground temperature is about 45 degrees Fahrenheit, sotick sometimes ticks will be out even if there is snow on the ground.  Because ticks become active even when it is relatively cold outside, many pet owners are caught by surprise in the early spring when they find a tick on their dog.  
Ticks find their hosts by detecting breath and body odors, or by sensing heat, moisture, vibrations, even shadows.  Ticks can't jump or fly, but they are well adapted to finding and latching onto hosts.  Ticks will rest on the tips of grasses or shrubs in a position known as "questing".  In this position, they hold onto the plant with some of it's legs, while having their first pair of legs outstretched, just waiting for a host to brush by.  Although Minnesota is home to several types of tick, it is the black-legged tick (Ixodes scapularis), commonly known as the "deer tick", which can transmit Lyme Disease (as well as other bacteria including anaplasmosis and babesiosis). 

Lyme disease is caused by the spirochete bacteria called Borrelia burgdorferi.  In humans, exposure to Lyme bacteria can be very serious.  The initial signs include the classic bull's eye lesion (erythema migrans) and flu-like symptoms. Some people will develop chronic, debilitating illness from Lyme disease.  Unlike people, we think that only 5-10% of all dogs exposed to Lyme bacteria ever get sick with the disease.  When clinical signs do occur, they typically start 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.  

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.  A dog that tests positive for the Lyme bacteria on a blood test, however, doesn't necessarily have Lyme disease and don't necessarily need to be treated.  

Veterinarians will routinely screen for exposure to Lyme bacteria.  (Often this test is done in conjunction with screening for exposure to heart worm disease and other tick borne diseases).   The most common test that veterinarians perform is an antibody test.  This test tells us if antibodies against the Lyme bacteria are present in the blood.  If this test is positive, it means that your dog has been exposed to the Lyme bacteria and has mounted an immune response to the bacteria, producing antibodies to it.    A positive test does not indicate that there is an "active" Lyme infection, only that the pet was exposed/infected in the past. 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.

It is important to know that many dogs that are positive for antibodies against Lyme infection will never develop any clinical symptoms (remember only about 10% show obvious signs).   When the test comes back positive, it doesn't mean that your dog has Lyme Disease, it means that your dog has been exposed to the Lyme bacteria.  You and your veterinarian will need to make a decision about what, if any action, should take place if this test shows up positive.  It is also important to know that there is not consensus in the veterinary community about how to manage a pet that is positive on the test and not showing clinical signs of Lyme disease.  The information provided below is what I recommend for my patients in the situation of a positive test in an otherwise healthy dog.

 
1.) I recommend screening for possible kidney problems.  The Lyme bacteria can create infection, but can also cause autoimmune problems in the dog.  A severe autoimmune problem secondary to exposure to Lyme bacteria is called "Lyme Nephritis".  In this disease, the filtering mechanism of the kidney, called the glomerulus is compromised.  The glomerulus is like a sieve, with holes in the sieve to filter out waste that needs to be excreted in the urine.  In a healthy kidney, the holes are big enough to allow waste products to leave the blood, but small enough to preserve important proteins and other blood products that the body needs.  If the holes in the sieve get too big, these important proteins will leave the blood and be excreted in the urine.  This is a very serious condition because the body sometimes can not keep up with the loss of protein through the kidneys, and the pet can become very ill and eventually die from this disease.  I recommend that all dogs that are newly diagnosed as positive on a Lyme test be screened for excessive protein loss in the urine through a test called the Urine Protein Creatinine ratio, or UPC.  If this test comes back positive, then more testing and treatment will likely follow.  If the test is negative, then I move on to recommendation 2 and 3 below.
 
2.) I recommend that all dogs that have been exposed to Lyme bacteria be on a tick preventative either year round (especially if the dog travels to more mild climates), or from the time of our first thaw to the time of our first hard freeze in Minnesota.  There are several great medications that can be used to protect against ticks.  One of the more well-known medications is called "Frontline".  This is a topical tick and flea preventative.  A new medication came out last year called "Nexgard".  This medication is a once a month oral medication and has proven to be very popular because you now don't need to put a topical medication on your dog. 
 
3.) I recommend that as a family, you review how to keep yourself safe from tick diseases.  Lyme bacteria cannot be transmitted from dogs to people, it can only be spread by the bite of an infected tick.  But, if your dog is positive, that means that you and your family have also likely been in an area that is endemic for Lyme Disease.    Keeping ticks off of your dog is important because ticks don't die after they take a blood meal.  They fall off the host and can reattach to another host later.  By using a tick preventative for your dog, you are helping protect your family from ticks.  Also, it is important that after you go for a walk in the woods, you do a tick check on your entire family.  It takes at least 36 hours for the Lyme bacteria to be transmitted from the tick to the host.  If ticks are identified and removed before that time period, then you can prevent the transmission of bacteria.  To remove a tick, use tweezers and try to remove as much of the tick as possible. 

There is a vaccine available to prevent Lyme disease in dogs.  The vaccine is very effective.  There is some controversy about whether or not a dog that has already been exposed to a natural infection of Lyme bacteria should be vaccinated against the disease.   To vaccinate or not vaccinate is a discussion that you should have with your veterinarian.  

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