What is Equine Granulocytic Anaplasmosis (EGA)
Anaplasmosis is a common, seasonal, non-contagious, tick-transmitted disease of equids observed where the Ixodes tick vector is found. Ixodes scapularis is found in the eastern half of the United States, while Ixodes pacificus is found along the entire west coast. Equine anaplasmosis has been reported in the United States, Canada, South America, Europe, Asia, and North Africa.
Clinical Signs:
- Acute infection is often characterized by lethargy
- A biphasic fever pattern, meaning the patient experiences two distinct periods of elevated temperature
- Reduced appetite
- Jaundice
- Fluid buildup (edema) in the horse’s legs
- Petechiation (small blood spots) on the mucous membrane
- Reluctance to move (Laminitis has not been associated with EGA)
- Horses less than four years of age have milder clinical signs and may present with only fever and mild depression
- Abortions are rare but can occur at any stage of gestation
- Mortality is rare, with most horses recovering over a 2–3-week period
- Infrequently severe myopathy characterized by fever and severe tying up or muscle pain and cramping during exercise
- Neurologic disease characterized by ataxia, recumbency, depression, and additional non-specific neurological deficits is rare.
Diagnosis: Veterinarians rely on a thorough clinical examination considering the horse’s history, geographic location, clinical signs like fever and lethargy. A blood test to identify characteristic inclusion bodies within the neutrophils of a peripheral blood smear. Laboratory abnormalities include low platelets (thrombocytopenia) low lymphocyte numbers, and anemia. The most definitive confirmation requires a PCR test.
Treatment: Tetracycline antibiotics administer intravenously or orally are used to treat EGA.
Prognosis: Mortality is rare with most horses recovering over a 2–3-week period.
Prevention: Tick control through environmental avoidance and diligent removal from horses remains the mainstay of EGA prevention. Anaplasmosis is not contagious between horses.