Lyme disease, just the name alone is enough to give veterinarians a headache. It is a complicated combination of exposure, infection, clinical signs, prevention and treatment. All of this is wrapped up in multiple controversies: is my animal at risk? Should we vaccinate? Should we test on a regular basis? What should be done once an animal tests positive? This article is going to try and sort out these questions and give some advice. But always remember whether it is Lyme or any other disease process the best place to discuss information, testing and treatment options is going to be with your veterinarian.
The critters that cause this and how they pass it on.
The problem starts with the Ixodes species of tick (specifically the Ixodes scapularis, or deer tick, in the eastern United States). These critters carry the bacteria that cause Lyme: specifically a gram negative spirochete called Borrelia burgdorferi (Bb). This infectious agent multiplies within the tick and will enter the animal at the end of the tick’s feeding cycle (approximately 48-72 hours after attachment). The agent then replicates in the skin at the tick bite site followed by migration through the tissue. Lyme disease is endemic to the northeastern United States (Massachusetts to Maryland), north central states and northern California.
Lyme does not begin to show signs in a dog for weeks to months following infection. The most common signs are fever, lack of appetite and joint pain. The most serious possible consequence of infection with Lyme disease is glomerular disease leading to renal failure (more on this later).
Stop it before it starts.
There are two main parts to prevention of Lyme disease: vaccination and tick prevention. Let’s tackle the second first. If you live in an endemic area (and, let’s face it, even if you don’t) it is VERY important that your dog have good tick prevention. There are many different medications/medicated products out there including Frontline, Revolution, Advantix and the Preventic collar. You may live in an area where there is resistance to one, or more, of these products. Discuss this with your veterinarian, make the best choice for your pet and make sure you are applying the chosen product correctly.
Now for vaccination. If you live in an endemic area then vaccination for Lyme disease is a good idea. It is a course of 2 vaccines given 3-4 weeks apart and then an annual booster. It is important to note at this point that according to most studies only approximately 5% of all dogs infected will actually show signs of disease. Also approximately 1-2% of vaccinated dogs will still get the disease (nothing is 100% effective). The take home message about prevention is this: Good tick prevention will help more than vaccination when it comes to keeping your dog from being exposed.
The test you don’t want to pass.
Before talking about testing I want to take a moment to discuss how the body reacts to infection. When the body is attacked it forms antibodies in response to the part of the bacteria (or other attacker) known as the antigen. This is also how vaccines work; they stimulate the body’s immune system to produce antibodies to a specific disease. If the body becomes exposed to the disease again it will recognize, and fight it off, faster. All tests for Lyme disease test for the antibody and not the antigen. This becomes important soon.
The most common test performed by small animal veterinarians is either the Snap-3 or Snap-4 test by Idexx laboratories. These two tests also test for heartworm disease, Lyme disease and other tick borne diseases. Many vets use these combination tests as a screening tool. Both are C6 tests that are sensitive too, and specific for, antibodies that have been formed due to natural exposure to Bb. C6 is a peptide (a unique area of one of the surface antigens of Bb). This peptide remains constant and always detectable in a body infected by Bb. Dogs exposed to Bb will test C6 positive within 3-5 weeks and can stay positive for years. Vaccines, however, do not contain this particular peptide. In other words, these tests will not come up positive for Bb in vaccinated animals.
So what’s the problem (or why all the controversy surrounding Lyme tests)? It lies in the fact that there is no proven correlation to testing positive and whether or not your dog will become symptomatic for Lyme disease. In fact-as stated above-approximately 90-95% of all dogs that test positive will not come down with the disease. In some endemic areas up to 70-90% of all healthy dogs will come up positive. Which leads to the question of whether or not testing on a regular basis is necessary and the diagnosis of Lyme disease?
So my dog is positive, now what?
The big question to ask yourself (or your vet will ask) is whether or not your dog is showing symptoms for Lyme. Do they have a fever? Are they eating? Are they limping? How’s their energy level? If the answers to all of these are good and normal then your dog is what we call an asymptomatic positive. And now the can of worms opens. I’m going to lay out what I’ve found in my research for this article. BUT this is where that disclaimer at the top bears repeating. This is my opinion and, as with any disease, you need to consult with your veterinarian before deciding on any treatment course.
Onward. Let’s hit the easy one first, your animal is positive for Lyme and has symptoms. They should, and will, be treated by your veterinarian. First choice antibiotics are doxycycline or amoxicillin. Typically dogs are treated for a month, though no one knows how long it takes to truly clear a dog of the carrier state (be clear of the disease). There is a second C6 test (called a Quant C6) that tests for the same antibodies as the SNAP test but it quantifies the level of antibody present. There is some use in using this test in dogs receiving treatment as you can test before and after to see if antibody levels falling which may give you an idea of if the treatment is working (more on that later-see below).
And the murky, scarier part.
Less easy one. Asymptomatic animals. First question, is it worth doing the Quant C6 test in these animals? Well, maybe. There is no evidence that antibody levels as measured by this test correlates to whether or not the dog will become symptomatic and, if so, the severity of the disease. Is it worth treating asymptomatic animals with a course of doxycycline? Well, maybe. There are arguments for this, primarily of the “if we don’t treat will my animal get worse later?” variety-no one knows the answer.
Arguments against include: overuse of antibiotics can lead to resistance (and no one wants doxycycline resistant Lyme disease), doxycycline can lead to unwanted side effects (typically vomiting, diarrhea and lowering of appetite) and, finally, back to most of these dogs will not get sick. So what’s the answer……that, for me, leads to the most concerning of all the potential consequences of Lyme disease.
A small percentage of dogs that get Lyme disease may get Lyme nephritis. This is a kidney disease thought (right now) to be caused by antibody/antigen immune complex formation that are deposited in the kidneys and lead to acute renal failure. These dogs have, unfortunately, a universally grave prognosis. They go downhill and die very quickly even with aggressive treatment. How can you tell if this rare consequence will occur in your dog? you can’t. BUT it does help answer whether or not you should treat asymptomatic dogs.
Back to my dog is an asymptomatic positive now what? First have their urine tested for protein. This should involve both a full urinalysis and a test called a urine protein/creatinine ratio. If these are both normal then these tests should be repeated every 6 or so months to make sure there are no changes. If either test is abnormal then full blood work should be performed (to include a chemistry profile and complete blood count). It is also a good idea to talk to your vet about testing for possible co-infectious agents (Anaplasmosis, Bartonella to name 2) as there is a reasonable chance the renal disease could have been caused by another infectious agent. If there is protein in the urine then, in my opinion, yes do a course of antibiotics. If there is no urine protein, no clinical signs of Lyme disease, you live in an endemic area where there is no way to know how long your dog has been positive, well, like I said, murky. Talk to your vet. You’ll get information, you’ll get confused (welcome to the club) and you’ll make the best decision for you and your pet.
One last thing, do you vaccinate an already positive dog? Most experts say no. Why? Vaccines are to help prevent infection in the first place, they’re infected now. The proverbial horse has left the barn. There is no evidence that vaccinating a positive animal will either help clear the disease faster and/or help prevent them being infected again.
The final word on Lyme: it is murky, it is confusing and one thing I can tell you for sure is if you get 5 vets in a room to talk about Lyme, especially about treatment of asymptomatic positive dogs, you will get at least 11 opinions at ever increasing volume levels. This is not a bad thing; in fact I think it’s a good one. The more questions means there are more people out there looking for answers. And maybe one day we’ll have them-but not today. Best advice I’ve got is Prevention First, with good prevention hopefully you won’t have to deal with decisions on treatment. But if you do discuss it with a veterinary professional and make the decision the suits you best. Good Luck.