Conditions or ailments that are the cause of a problem that you see - your observation.

Your vet may diagnose

Equine Granulocytic Ehrlichiosis, EGE

Synonyms: Anaplasmosis, Ehrlichia equi


Ehrlichiosis is a tick-borne disease caused by the organism Anaplasma phagocytophila. This organism is found in ticks of the genus Ixodes. It gains access to the bloodstream and colonizes certain types of inflammatory blood cells (granulocytes), and causes inflammation of blood vessels (vasculitis).

This disease is regional, being common in Northern California but has also been diagnosed in a handful of other Western states and in Europe.

Signs of disease include depression, loss of appetite, reluctance to move, fever, leg and belly swelling, wobbliness and yellow gums.

This disease can range in severity from mild to severe. In horses less than 1 year old, it tends to be mild and often limited to fever and mild depression. In adults, disease can last for 7-12 days and can be quite severe.

Diagnosis requires identification of the organism on a blood smear, and other laboratory blood tests.

Treatment requires the use of the tetracycline antibiotics. This requires a diagnosis or at least suspicion of disease.

my vet's role



Other conditions or ailments that might also need to be ruled out by a vet.

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The prognosis depends on the severity of the disease coupled with the promptness of diagnosis and provision of effective treatment.

The prognosis is good with treatment with the antibiotic oxytetracycline. Other antibiotic classes are not effective. Horses not treated with oxytetracycline may have severe and lengthy illness, but usually survive. These horses often lose weight and occasionally develop complications like pneumonia or laminitis.

Once a horse recovers from EGE, they have immunity for at least 2 years. Disease is rare in horses less than 1 year old.

my role


I might observe

You might make these observations when a horse has this condition.

Very Common
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Questions To Ask Your Vet:
  • What preventative measures can be taken to reduce the likelihood of disease?
  • What is the risk of this disease in my geographic region?

There is no vaccine available. Efforts should be made to decrease the population of ticks in the environment, including regular mowing of tall grass where possible. Reduction of ticks on horses might include the use of anti-tick sprays and regular shampooing with an anti-tick shampoo.

In areas where ticks are prevalent, it is important to frequently examine horses and other animals for ticks and remove them promptly. Insecticide impregnated cattle ear tags can be attached to a collar or halter.

All of that said, horses living in endemic areas often become at least partially immune to the disease.

further reading & resources

Related References:

Lavoie JP, Hinchcliff KW eds. Blackwell's 5 Minute Vet Consult: Equine. 2nd Ed. Ames: Wiley Blackwell 2008.

Higgins AJ, Snyder JR eds. The Equine Manual. 2nd Ed. Edinburgh: Elsevier Saunders 2006.

Author: Doug Thal DVM Dipl. ABVP