Tick-borne diseases in Wisconsin
We frequently have patients test positive for tick-borne diseases when running our combination heartworm tests. Fortunately, most of the dogs with positive tests never develop any symptoms of illness, especially if we can catch the disease early. It’s scary to think your dog might have a dreadful disease but in most cases the outcome is good.
Most pet owners have heard about Lyme disease but are not familiar with the other diseases ticks can carry. In addition to Lyme disease, ticks carry Anaplasmosis and two strains of Ehrlichiosis. Rocky Mountain spotted fever is also a tick-borne disease but we have no in-house test for it. Despite the name, RMSF occurs most often in the southeastern U.S. Below is a short update on the tick-borne infections we see most often here in Wisconsin.
Many of our clients assume that if they are using a tick preventive product and are not seeing ticks on their dogs that they cannot have picked up one of these infections. Alas, we have a lot of patients who have been exposed to one or more tick-borne diseases despite these facts.
No tick preventive is 100% effective, which is why we vaccinate for Lyme disease as well as using preventive products. It also takes hours for the tick to die once it has bitten the dog and acquired the preventative drug or chemical. During that time, disease can be transmitted, even if the tick dies and falls off the dog. As for not seeing ticks, larval deer ticks are barely visible to the naked eye and the larval stage is the most likely stage to transmit Lyme disease to dogs.
We recommend doing everything you can to prevent tick-borne diseases – vaccinate, use high quality preventive products and have your dog tested annually so we can catch infection early.
Lyme disease is carried almost exclusively by deer ticks here in the Midwest. Fall and winter are the peak seasons for this species. October to April are the months you should be worried about, so don’t stop flea and tick preventives during the winter! Fall is when the most cases of Lyme disease are diagnosed.
There are more than 100 different strains of the Borrelia burgdorferi bacteria that cause Lyme disease, which is thought to be why some dogs get sick and others don’t. It depends on which strain they have picked up. Already having one strain of the disease gives no resistance to other strains, so the primary goal is to not let the dog continue to accumulate infections via continued exposure to ticks. The strain your dog already has may not make him sick but the next one might.
Many strains are now resistant to the antibiotics we have been using for the past forty years. The new recommendation is to use a 3rd generation cephalosporin antibiotic such as cefovecin, which is administered in a two week injection, or cefpodoxime tablets. Even with effective treatment, recurrence of Lyme disease symptoms is not uncommon, so treatment may need to be repeated later on.
Many dogs who become infected with Lyme disease never show obvious outward signs of infection but this does not mean they have not suffered subtle organ damage. We will test your pet’s urine for kidney function if we diagnose Lyme disease, to detect damage that can eventually cause kidney failure. The strain of Lyme we see the most in our area typically causes kidney disease but not the classic symptoms of lameness, fever and swollen joints. We recommend additional bloodwork too, in case other, less common abnormalities arise, but the urine test is the most important.
A recent study of Lyme-positive dogs showed that joint damage can be subtle. Even dogs without apparent lameness may have damage inside the joints, which will lead to early onset arthritis. This means that we may recommend antibiotic treatment if your dog tests positive for Lyme, even if he or she does not have any symptoms that we can see right now. This is a change in our protocol. The previous recommendation was to only treat for Lyme if symptoms developed.
This disease, caused by Anaplasma bacteria, is spread by several species of ticks and is common in Wisconsin. It’s the least likely of the tick-borne diseases to cause actual illness. Most dogs can handle the infection on their own, without needing antibiotics. If your dog tests positive for Anaplasmosis we will recommend a complete blood count (CBC) to look for a low platelet count, the most common symptom. (If your dog doesn’t have enough platelets the blood won’t clot properly and severe bleeding could result.) If the CBC is normal we usually don’t need to treat for it.
As with all the tick-borne diseases, once the dog has acquired infection and tests positive the test will continue to be positive for several years, until the immune system has completely eradicated the bacteria. If a dog acquires another tick-borne disease during this time or the pet becomes immune-compromised illness may result.
Ehrlichiosis: Becoming More Common
Ehrlichiosis (air-lick-ee-ohsis) is the disease caused by Ehrlichia bacteria, which is spread to dogs via tick bites but not usually by deer ticks. Lone Star ticks are the most frequent host ticks for the disease here in Wisconsin. Ehrlichiosis is the most deadly of the tick-borne diseases found here. It is becoming more common in our state because Lone Star ticks have been expanding their range. In the past, the few cases we saw were in dogs that had traveled to or from the Southeastern U.S. but that’s often not the case anymore.
Many, many dogs in Wisconsin test positive for Lyme disease or Anaplasmosis without developing symptoms or needing treatment. Ehrlichiosis is always treated with antibiotics, however, even if no symptoms are present, because it is much more likely to cause serious illness.
Ehrlichia can cause fever, lameness in multiple joints, kidney disease, neurological disorders such as seizures and coma, and/or bone marrow damage. Lyme disease can cause these symptoms as well but Lyme isn’t usually as severe. For example, a dog with Lyme disease has a 43% increase in risk for kidney disease but a dog with Ehrlichiosis has a 300% increase in risk.
When we find Ehrlichia on our test we always screen for kidney damage, anemia, low platelet count and other possible abnormalities, via urine and blood testing, and we treat it with the antibiotic doxycycline. There is often a long lag period between acquiring the disease from the tick and the onset of symptoms. If we can treat an infected dog early on we can usually prevent symptoms altogether, so that’s our goal.
Dogs who are infected with multiple tick-borne infections are usually the sickest. Ehrlichiosis plus Lyme disease is often a fatal combination, even with aggressive treatment. The immune system may be able to combat one disease but if another is added serious illness is much more likely.
The important thing is to be aware that your dog probably will be exposed to ticks carrying these bacteria sooner or later. The positive blood tests we see are red flags that tell us we need to be very careful to protect our pets (and ourselves) from ticks, so they don’t accumulate tick-borne diseases and eventually overwhelm their immune systems.
We also look for hidden symptoms that mean the bacteria is causing illness that is not easily detectable. Lyme disease can damage the kidneys so we would test for protein loss in the urine that might indicate damage is occurring inside. Similarly, Anaplasmosis can cause a low platelet count.
We have effective vaccines to protect dogs from Lyme disease but we have none for Ehrlichiosis, Anaplasmosis or Rocky Mountain spotted fever. To prevent these infections, use high quality tick prevention products all year ‘round. We don’t recommend over-the-counter tick control products in most cases, as many of these are neither as effective nor as safe as prescription products. The longer a tick is attached, the higher the chance that an infectious disease will make it into the pet, so we want the tick to die and fall off within a few hours of biting your dog, and of course we want every tick to die.
If we discover there is a problem we will treat your dog with antibiotics; doxycycline for Anaplasmosis and Ehrlichiosis, and ceftiofur or cefpodoxime for Lyme disease. We would also need to treat the organs affected – for example with a special diet for kidney disease or a blood transfusion for extremely low platelet count. We need to know what damage has been done so we need to diagnose the problem rather than just dispense antibiotics when they may not be necessary.
If your pet has symptoms that could be caused by one of these infections, such as lameness in the case of Lyme disease, further testing may be needed to prove that the tick-borne disease is actually what is causing the problem. Lameness could be due to Lyme disease but also arthritis, a torn ligament or a sprain.
If Anaplasmosis is not causing any symptoms there is no need to give antibiotics. For Lyme and Ehrlichiosis, antibiotics knock the bacteria back and allow the dog to recover from illness caused by them, but it is impossible to eliminate either of these infections from their bodies entirely. Dogs may continue to harbor these organisms in their bodies even after taking antibiotics and will test positive for them for years afterwards as well.
A positive test doesn’t mean a dog will become ill, and in fact most dogs don’t. When needed, antibiotics are usually effective. If your dog is at risk, be sure to vaccinate for Lyme disease and use those flea and tick preventatives faithfully!