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Ehrlichiosis

Randy Walker DVM

About Ehrlichiosis...

Ehrlichiosis (commonly known as "tick fever") is a fairly common disease of dogs in many parts of the world. Ehrlichiosis is caused by a microscopic organism called Ehrlichia canis.

What Are The Symptoms Of Ehrlichiosis (Tick Fever)?

Ehrlichiosis (tick fever) can cause many different clinical. syndromes and not all of them can be covered in this information sheet. The three most common forms Ehrlichiosis (tick fever) can take are (1) acute (meaning quick onset) illness (2) chronic (meaning lingering) illness and (3) neurologic (pertaining to the brain or spinal cord) illness.

Acute Ehrlichiosis (tick fever) is the most commonly encountered of these syndromes in our area. The dog with acute Ehrlichiosis usually has a moderate to high fever (often very high), lethargy (loss of energy), loss of appetite, weight loss, and enlarged lymph nodes (usually). The patient with acute Ehrlichiosis will also sometimes experience spontaneous bleeding such as nose bleeds (due to the disease inhibiting the blood's ability to clot) conjunctivitis (inflammation of the eyes), pneumonitis (inflammation of the lungs), edema (swelling due to fluid accumulation in the lower parts of the body) and vomiting are sometimes seen with acute Ehrlichiosis.

In cases of chronic Ehrlichiosis (tick fever) the symptoms can be more subtle with progressive weight loss and unthriftiness being common clinical signs. Sometimes dogs with chronic Ehrlichiosis will have a nose bleed (or repeated nose bleeds) as the main symptom. Ehrlichiosis attacks the red blood cells (which carry oxygen ) and the white blood cells (which fight infection) and this commonly results in life threatening deficiencies of both of these blood components. Dogs with chronic Ehrlichiosis often have problems with bleeding under the skin and into the body cavities and sometimes this bleeding can be fatal. Sometimes Ehrlichiosis (tick fever) can cause an inflammation of the brain (called a meningitis) which can result in mental dullness, seizures, or coma. Ehrlichiosis (tick fever) can also sometimes cause other disease syndromes in the body which are too numerous to cover here.

How Is Ehrlichiosis (Tick Fever) Transmitted?

The main route of spread is by the bite of the brown dog tick (Rhipicephalus sanguineus). It only takes the bite of one carrier tick to transmit the disease. The incubation period (that time from when the dog is bitten until clinical signs develop) is usually 10-14 days. For this reason we often see patients who are sick with a laboratory confirmed case of Ehrlichiosis (tick fever) and find no ticks on their body. It is not uncommon for a dog to have Ehrlichiosis and not to be able to find ticks on the dog's body.

How Is Ehrlichiosis Diagnosed?

Ehrlichiosis (tick fever) is diagnosed by a blood test which looks specifically at the level of antibodies toward Ehrlichia canis, which is the microscopic organism which causes this disease.

How Reliable Is The Antibody Test For Ehrlichiosis (Tick Fever)?

As a general. rule, the antibody test for Ehrlichiosis (tick fever) is quite reliable. As with all antibody laboratory tests, however, the Ehrlichia titer results must be interpreted in view of the history and clinical symptoms. In a small number of cases, if a dog has recently been infected with Ehrlichiosis it can still give us a negative result on the lab test. This is because the disease hasn't been in the dog's system long enough to simulate enough antibodies to register on the test. In his case the test gives us a "false-negative", meaning that the test said the disease was not present when it really was. When such cases are suspected we usually recommend checking the antibody titer again in several. weeks to see if the titer is increasing. In a small number of other cases, a dog can have a significant number of Ehrlichia antibodies in their blood stream, yet not have Ehrlichiosis at that time. This can occasionally happen because, when a dog becomes exposed to Ehrlichiosis (which is quite common in our region), the dog can have a large number of these antibodies in their system for a period of time thereafter. If the dog contracts tick fever and recovers from it, then is exposed again, this will stimulate antibody production although the patient doesn't have tick fever at that time. Here again, we usually follow-up on the Ehrlichiosis antibody titer at a future date to see in which direction (up or down) the numbers of antibodies are shifting and correlate this with clinical signs and response to treatment. It should also be emphasized that it's really a small percentage of cases which fall into these "gray areas".

How Is Ehrlichiosis (Tick Fever) Treated?

In most cases Ehrlichiosis is treated with a member of the tetracycline family of antibiotics (tetracycline, oxytetracycline, etc). Because the Ehrlichia organism can "hide" in the white blood cells (and therefore not easily be eliminated by our antibiotic) we usually continue antibiotic therapy for several weeks and then analyze a blood sample to make sure the organism is being eliminated.

What Is The Prognosis For Ehrlichiosis (Tick Fever)?

This depends greatly on the form of the disease encountered (acute or chronic) and the patient's personal factors (age, other ongoing diseases, breed, etc.) Most cases of acute Ehrlichiosis in relatively young dogs respond well to tetracycline and usually make a complete recovery. Chronic cases (especially in older and/or debilitated dogs) are usually much more difficult to get under control and a significant percentage of these will not respond to treatment and can ultimately be fatal. Some specific breeds (especially Doberman Pincher's, Rottweilers, and German Shepherds among others) will have a harder time recovering from Ehrlichiosis. No two cases of Ehrlichiosis will be quite the same.

Can Some Dogs Become Carriers Of Ehrlichiosis?

Yes, some dogs can become chronic carriers of Ehrlichiosis. This means that the patient has reached a "stand-off" with the disease in which the dog can't eliminate the organisms from its body but is still able to lead a relatively normal life. The chronic carrier state is a source of exposure (a "reservoir") for other dogs.

What Human Disease Can Ehrlichiosis Best Be Compared To?

Ehrlichia canis (the organism which causes tick fever) is a Rickettsia (which can be thought of as a primitive form of bacteria) and this is the same family of organisms which cause Rocky Mountain Spotted Fever, Babesiosis, and Lyme disease among others in both dogs and humans.

Can Ehrlichiosis (Tick Fever) Be Transmitted To Humans?

Although it has been reported, Ehrlichiosis is quite rare in humans. You only catch Ehrlichiosis (tick fever) from a carrier tick (specifically the brown dog tick) and cannot catch it directly from a sick dog.

Can My Cat Catch Ehrlichiosis?

No. Ehrlichiosis has not been reported in cats (although they can get some other related diseases).


- Randy Walker DVM
Sun Lakes Animal Clinic
May 15,2004



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