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.