Equine and Human Granulocytic Ehrlichiosis

The same tick that spreads Lyme disease appears to be the culprit in another disease of humans and horses, granulocytic ehrlichiosis. This condition, which mimics Lyme disease, was once thought to be two separate diseases. Through equine research headed by the UC Davis Center for Equine Health's Dr. John Madigan, it was found that both conditions, Equine Granulocytic Ehrlichiosis (EGE) and Human  Granulocytic Ehrlichiosis (HGE), were caused by a bacterial organism called Ehrlichia equi (E. equi).

The clinical signs of EGE in horses include fever, depression, jaundice, limb swelling, incoordination, low white blood cell count and a decreased number of blood platelets. In humans, the clinical signs of HGE mimic the flu and include fever, headache, shaking, chills and nausea.

EGE and HGE are easily treated in the early stages using tetracycline antibiotics.  If not treated quickly with appropriate antibiotics, the organism may spread throughout the body causing significant damage to internal organs and possible death in both horses and humans. Using blood tests, diagnosis of EGE and HGE is made by the identification of EGE and HE is made by the identification of  E. equi in the white blood cells.

UC Davis researchers developed a PCR (polymerase chain reaction) test that is highly sensitive and specific for detecting E. equi in blood samples from affected horses. The equine research helped to identify ticks as the vector of this disease in both humans and horses and has been used as a model for diagnosis and treatment of EGE/HGE.

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