The American Association of Equine Practitioners (AAEP) has published on its website comprehensive guidelines to assist practitioners with identification, treatment, mitigation of risk factors and other considerations of Equine Granulocytic Anaplasmosis (EGA), a common, seasonal, non-contagious, tick-transmitted disease of equids observed where the Ixodes tick vector is found.

EGA has been reported in the U.S., Canada, South America, Europe, Asia and North Africa. Acute infection is often characterized by lethargy, biphasic fever and reduced appetite, followed in 3-to-5 days by more severe signs of icterus, limb edema, mucous membrane penetration and reluctance to move. Horses under four have milder clinical signs. Mortality is rare, and most horses recover within two-to-three weeks.

“EGA is an important tick-borne disease in many regions of the United States and abroad,” said Ron Vin, DVM, DACVIM (LAIM), equine internal medicine specialist at the Myhre Equine Clinic in Rochester, N.H. “Our understanding of EGA has advanced substantially in recent decades, and we hope these guidelines will provide equine practitioners with the most current information available for diagnosis and treating EGA in their patients.”

While no standard treatment protocol exists, intravenous administration of oxytetracycline at 7 mg/kg body weight once daily for five-to-seven days is commonly used in practice. Dilution of tetracycline in saline (not LRS) and slow administration IV is recommended, as is collecting blood for PCR and blood smear assessment before initiating treatment. Alternate treatment options include oral doxycycline (10 mg/kg BID) or minocycline (4 mg/kg orally BID).

Tick control through environmental avoidance and diligent removal from horses is the most effective control measure. These include use of spray and spot-on tick repellant products as well as removal of leaves and woody debris, pasture mowing and maintaining dry, well-lit paddocks whenever possible.

Dr. Vin co-authored the EGA Guidelines with John Madigan, DVM, MS, DACVIM, DACAW, professor emeritus of medicine and epidemiology at the University of California, Davis; and Kathleen Mullen, DVM, MS, DACVIM, equine internal medicine specialist at Littleton Equine Medical Center in Littleton, Colo., and veterinary postdoctoral fellow at the University of Colorado Anschutz Medical Campus. The guidelines were reviewed and approved by the AAEP’s Infectious Disease Committee and board of directors. View the guidelines or save them to your mobile device at

Besides EGA, AAEP guidelines for 25 additional equine infectious diseases can be found at In addition, six foreign animal disease guidelines are available at

About AAEP

The American Association of Equine Practitioners, headquartered in Lexington, Ky., was founded in 1954 as a non-profit organization dedicated to the health and welfare of the horse. Currently, AAEP reaches more than 5 million horse owners through its over 9,000 members worldwide and is actively involved in ethics issues, practice management, research and continuing education in the equine veterinary profession and horse industry.

Post Type

  • Press Release


  • Equine Granulocytic Anaplasmosis (EGA)
  • Infectious Diseases

Publish Date

August 14, 2023

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