Lyme and Erlichia and Anaplasma, Oh My!
March 29, 2012
There’s no doubt that we Minnesotans are coming off of an unseasonably warm winter. While everyone (except winter sport enthusiasts) is still basking in the glow of memories of warm temperatures and almost nonexistent snowfall, we all know there’s no such thing as a free lunch. Unfortunately, part of paying the warm winter piper means putting up with ticks, which are emerging earlier and in higher numbers than usual. And – as if they weren’t unpleasant enough on their own – where there are deer ticks, Lyme disease can follow.
Welcome to Lyme Disease 101
So it all starts with those ticks. No, mice. No, spirochetes. No, deer… or birds? Wait, let’s back up a bit. This is getting complicated already and we just started.
Step One: Don’t Panic!
There are three tick-borne diseases of concern in our area: Lyme disease, Anaplasmosis, and Erlichiosis. They are caused by different but related species of bacteria called spirochetes. While this article specifically addresses Lyme, the three diseases act very similar and except where noted can be thought of interchangeably.
Lyme acts very different in dogs than it does in humans. In humans, Lyme disease is notorious for causing serious long term problems such as relapsing attacks of arthritis or neurologic disease in a significant number of people (up to 60% by some reports). The majority of people (up to 80%) will at least experience a rash and/or symptoms of the flu within a few weeks of being infected.
In dogs, Lyme is a relatively minor infection in the vast majority of cases. 95% or more of dogs that have been infected never show any symptoms at all. Treatment with appropriate antibiotics is inexpensive, safe, and effective and long-term complications are extremely rare. Common symptoms of Lyme in dogs include waxing and waning fever, malaise or lethargy, poor appetite, shifting leg lameness or generalized discomfort. Dogs do not get the typical “bulls eye” rash that is common in people.
A type of chronic kidney disease called glomerulonephritis may be associated with Lyme disease in certain individuals when antibodies to Lyme clump up with the spirochete and “clog” the filter of the kidney. However, this is rare (exact numbers are not available but it is thought to be a fraction of the approximately 5% of dogs who get sick from Lyme in the first place), unpredictable, and does not seem to have any definable risk factors such as how quickly a dog was diagnosed or treated, how long it was treated, or whether it was vaccinated or not.
Prevention 101: Knowledge is Half the Battle
There are 3 main strategies for preventing Lyme: Tick checks/removing ticks, using a tick control product, and vaccination (available only for Lyme disease, not Anaplasmosis or Erlichiosis).
Which brings us to a lesson in ticks. “Why do we need to know this stuff?” Because as unpleasant as ticks may be, understanding their life cycle can help us understand how Lyme is spread, and that helps us understand how to prevent disease.
Before diving into the ticks themselves, a short vocabulary lesson is in order. Ahost is any mammal that a tick attaches to and feeds from. A reservoir(sometimes also called a carrier) is an organism that carries the infectious cause of a disease in its body but does not get sick from it. A vector is an organism that spreads the infectious cause from one organism to another. For example, in Minnesota the deer tick is the vector that spreads the spirochetes that cause Lyme from wildlife reservoirs (such as the white-footed mouse) to any other host(such as another mouse, a bird, deer, dog, human, cat, etc.).
Deer tick eggs hatch in the spring. These newly-hatched ticks are called larvaeand are extremely small. The larvae attach to the first available host, feed, then drop off and molt into a teenage-like stage called a nymph. The nymphs remain dormant until the following spring/summer, when they attach to a second host, feed, then drop off and molt into their final adult stage. That fall or the following spring, the adults attach to a new host, where the females feed for a third time, mate, lay their eggs, and die. Adult males do not feed from the third host, they simply hang around waiting for a female to mate with.
The spirochetes that cause Lyme cannot survive in the outside world. They can only live circulating in the blood of reservoir mammals or in the gut of a tick. (In our area, the deer tick is the only suitable tick in which Lyme spirochetes can live; wood ticks can transmit rocky mountain spotted fever, which is not found in our area, and possibly erlichiosis.) Any deer tick can potentially ingest these spirochetes with each blood meal they take from an infected reservoir. If this happens, the spirochetes live in the deer tick’s gut until its next meal, when it can potentially transmit them to the next host.
How exactly is the spirochete transmitted? Since they suck blood, in order to feed properly ticks need to prevent their host’s blood from clotting. To accomplish this, they regurgitate anticoagulant enzymes from their gut into the wound where they have attached. When this happens, the spirochetes are also regurgitated into the wound. However, this process of regurgitation and feeding takes time – at least 24-48 hours after attachment.
That time frame presents an opportunity to prevent Lyme by looking for and removing ticks every day. If ticks are found and removed within 24-48 hours of attachment, they cannot transmit Lyme because they simply do not have enough time. Ticks can attach to any part of a dog’s body but are commonly found by owners around the head and ears. This may be because on more accessible areas, dogs are able to find and remove their own ticks by nibbling them off.
Every deer tick found and removed is one fewer chance for Lyme to spread, but of course life isn’t simple enough to rely on tick checks alone for prevention. Deer ticks, especially the nymphs, are small and easily missed — especially on long-haired or dark-colored dogs. Another opportunity to prevent Lyme is using products to repel or kill ticks. There are a variety of products available for this purpose and it is beyond the scope of this article to discuss them all. You can speak with one of our veterinarians or technicians to discuss specific products.
A third opportunity to prevent Lyme disease is vaccination. (There is no vaccine available to protect against Erlichia or Anaplasma.) The decision to vaccinate against Lyme disease should be made on an individual basis. Factors to consider include lifestyle, exposure risks, and general health of each individual dog. Again, the decision of whether to vaccinate an individual dog is beyond the scope of this article and should be discussed with one of our veterinarians.
Testing: A Blessing and a Curse
There are two common ways to test for Lyme. Both test for the presence ofantibodies (proteins that help fight disease) that the body has produced against Lyme, but they work and give their results in slightly different ways.
The first is called a snap test (sometimes called a 4DX). This simple test can be done at the clinic in about 15 minutes, and much like an over the counter pregnancy test it indicates the presence of antibodies with a simple yes/no color change – in this case, the appearance of a blue dot. Lyme, Erlichia, and Anaplasma can all be detected and differentiated from one another on the snap test.
The other test is called a titer, which measures the amount of antibodies in the blood and expresses them as a number. This test must be sent to an outside laboratory and takes days to weeks to get results. The advantage to a titer is that in some cases, if multiple titers are done over a long time period of week it may be easier to document that a dog truly has an active infection right now. The disadvantage is the time involved in making such a determination – practically, a sick dog cannot wait for weeks to confirm a diagnosis.
Since 90% or more of dogs develop antibodies to Lyme after being exposed whether they get sick or not, only about 5% of dogs get sick at all, and antibodies to Lyme may persist for years in the bloodstream regardless of illness or treatment, it is unfortunately not at all simple or straightforward to interpret a positive test result. The positive test only tells us that a dog has been exposed to Lyme and its body is making antibodies, not when the exposure occurred or if/when the dog has been or will be sick.
Because of these limitations, it is best to limit use of antibody tests to confirm the presence of antibodies to Lyme in a dog whose exposure history and symptoms are consistent with possibly being sick from Lyme rather than as a yearlyscreening test (that is, a test used on all dogs to see if they have ever been exposed to Lyme).
In a dog with symptoms of Lyme disease and a positive test, another test called acomplete blood count (CBC) can be used to help confirm the diagnosis. Changes such as low platelets often accompany Lyme disease, and the Anaplasma or Erlichia organisms can sometimes actually be seen within white blood cells.
So… Treat or Don’t Treat?
There is no such thing as a blanket recommendation for whether to treat an individual dog for Lyme disease. This is something to be decided for each patient depending on symptoms and test results together. Since exposure does not lead to disease in the vast majority of the cases, it is generally not recommended to treat a dog with a positive test result if there are no symptoms, but even that is not set in stone. This is a decision that must be made by a pet owner and veterinarian together.
Sources and Helpful Links