What is Ehrlichia?

Ehrlichia, named for the Dr. Ehrlich who first described them, is a special type of bacteria which infect and live within the white blood cells of their hosts. Different types of Ehrlichia live in different types of white blood cells. Hosts can be human, pet, or wild animals. They are spread from host to host by tick bites and their intracellular location makes them difficult to remove as most antibiotics do not penetrate to the inside of cells.

What ticks are involved in Ehrlichia?

Different Ehrlichia species are spread by different types of tick.

The Brown Dog Tick (Rhipicephalus sanguineus) usually spreads Ehrlichia canis, Ehrlichia ewingii, and other diseases.

Brown Dog Tick

Brown Dog Tick

The Lone Star Tick (Amblyomma americanum) is the main vector of Ehrlichia ewingii. (Note the “star” on the tick’s main body.)

Lone Star Tick

Lone Star Tick

It is important to note, where there are ticks there are many tick-borne diseases: Lyme Disease, Babesia infection, Anaplasma, Ehrlichia, and probably some agents we do not even know of yet. It is not surprising for a given patient living in a tick area to be infected with multiple blood parasites.

Stages of Erlichia

Acute Stage

This is generally a very mild phase and occurs 1-3 weeks after the host is bitten by the tick. The Ehrlichia organism is replicated in this time period and attaching to white blood cell membranes. During this time the platelet count will drop and an immune-mediated platelet destruction will occur. The dog will be listless, off food, and may have enlarged lymph nodes. There may be fever as well but rarely does this phase kill a dog. Most clear the organism on their own but some will go on to the next phase.

Subclinical Stage

In this phase, the dog appears normal. The organism has sequestered in the spleen and is essentially hiding out there. Dogs can stay in this phase for months or even years. The only hint that Ehrlichia is hiding is a somewhat reduced platelet count and/or elevated globulin level on a blood test. Blood protein is divided into Albumin (an important carrier protein) and Globulins (every other blood protein including antibodies.) Long term stimulation of the immune system will elevate globulins.

Chronic Stage

In this phase the dog gets sick again. Up to 60% of dogs infected with Ehrlichia canis will have abnormal bleeding due to reduced platelets numbers. Deep inflammation in the eyes called “uveitis” may occur as a result of the long term immune stimulation. Neurological effects may also be seen. Glomeruloneprhitis, resulting in serious urinary protein loss, can also result. Increased globulin levels are almost always seen in this stage, albumin is often low.

Infections with Ehrlichia ewingii tend to produce arthritis in addition to the above scenario.

How Diagnosis is Made?

Diagnosis does not rest on a single test but instead on a collection of results. The first step is to find a constellation of typical findings:

  • A dog with fever, enlarged lymph nodes, bleeding, or arthritis in multiple joints.
  • Low platelet numbers, high globulin levels, and mild anemia on blood testing.

When Ehrlichia is suspected, a blood test for antibodies against Ehrlichia organisms can be ordered. A positive test indicates that the dog has been exposed to Ehrlichia and does not imply active current infection necessarily. A negative titer does not fully rule out Ehrlichia, either, as a very sick patient will be too sick to produce antibodies and an early case may not yet have started to produce antibodies. The antibody level or “titer” can be done with an IFA (immunofluorescent antibody) or by ELISA (Enzyme-linked Immunosorbant assay). It takes 6-9 months after infection for titers to begin to drop.

How to Treat It?

Despite being one of the oldest antibiotics in use, tetracycline is probably the most effective against Ehrlichia (and any other intracellular blood parasite for that matter). Doxycycline, a more modern derivative, has a more convenient dosing schedule and has become more popular. Expect at least a month of treatment to be needed. Response is initially rapid (improvement is notable in the first few days).

If immune-mediated secondary reactions to the Ehrlichia are a problem (such as immune-mediated arthritis, or immune-mediated platelet loss) corticosteroids such as prednisone can be used to palliate the situation while the antibiotics are starting to work.

After infection, it is possible to become re-infected; immunity is not lasting after a previous infection.

Article source is Mar Vista Vet
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