Tick Fever

Many dog owners do not know this about the tick: other than being a blood sucking parasite, a single tick may kill your dog.

Tick fever, or in its scientific name – Ehrlichiosis, is caused by a bacteria that infects white blood cells and lives in them. The common pathogen in Israel is Ehrlichia canis and it is transferred from host to host by the brown dog tick, Rhipicephalus sanguineus. Hence the name "Tick Fever".

The disease has 3 stages – acute, subclinical and chronic.

The acute stage occurs 1-3 weeks after the dog is bitten by an infected tick. This stage is usually mild. During this stage the dog will seem tired, decreased appetite and sometimes fever. This stage is rarely lethal. In most cases, if the dog is treated on time, he will be able to get rid of the bacteria. If the treatment is not adequate the disease will progress to the next stage.

In the subclinical stage the bacteria hides from the immune system in the spleen so the dog seems normal. A dog can stay in this state for months or even years. Despite the normal clinical appearance, a blood test may show some changes in the CBC, such as a mild decrease in the platelet count.

In the chronic stage the dog will show clinical signs again. These may be fever, tiredness, inappetence and paleness. We might also see hemorrhages or hematomas as a result of the decrease in platelet count. 

Diagnosis is never based on a single finding but on several tests. When a dog comes to the clinic and we find enlarged lymph nodes and fever we do a complete blood test (CBC and chemistry). Even more so when it is known that the dog had ticks or if we see signs of bleeding. When we do a CBC we will see a decrease in white blood cell count as a result of the body's destruction of the white blood cells containing the bacteria in an attempt to get rid of the bacteria. We will also see a decrease in platelet count as a result of vasculitis. We might also see anemia. In chronic cases we will also see a decrease in protein (albumin) levels and an increase in globulin (antibodies, mainly) levels. Such findings may be seen in other diseases so the next step would be a serology test and/or a PCR test.

The serology test tests for the presence of antibodies against the Ehrlichia canis in the dog's blood. The test's main disadvantages are that a dog that had tick fever in the past will be seropositive even if he did not have tick fever at the moment of testing as well as that a dog in early stages of the acute stage of the disease may be seronegative since he did not produce enough antibodies yet. The main advantage of this test is that it is fast, it is available in the clinic and is relatively cheap.

The PCR test tests for the presence of Ehrlichia canis's DNA in the dog's blood. The test's main disadvantages are that it is more expensive than the serology test and the fact that the results are not immediate but take a few days to arrive. The main advantage of this test is that a positive or negative result is definite.

Treatment against tick fever is done with antibiotics combined with a drug call imidocarb. Usually treatment is several weeks long until blood tests (preferably PCR) show the bacteria is out of the system and the dog is healthy. In some cases we may use steroids in order to deal with secondary immune reactions until the antibiotics start to work.

It is important to note that the best and simplest way to deal with tick fever is prevention by tick repelling products in spot-on ampoules or collars. The ticks do not transfer the bacteria from one tick to another and must get infected by feeding on an infected dogs so, if we all treat our dogs against ticks, it is possible that in the future tick fever will no longer exist.