Also known as equine granulocytic anaplasmosis (EGA) or equine anaplasmosis. This is a relatively new disease, first described in the United States in 1969 but now increasingly recognised both in the US and Europe.
Anaplasma phagocytophilum infection
Anaplasmosis is an infection caused by the bacterium A. phagocytophilum.
A.phagocytophilum infection is tick-borne, spread by Ixodes ricinus (a sheep tick), and often occurs from spring to autumn due to increased tick activity at this time of year.
Following an incubation period of 10 days, signs of infection may include loss of appetite, a fever, depression, reluctance to move, oedema (filled legs) and incoordination. The disease is self-limiting and clinical signs only last approximately 7-14 days.
Prompt diagnosis and treatment of A. phagocytophilum infection can speed recovery, so if your horse develops these signs, call your vet as soon as possible.
The clinical signs associated with the disease are not specific; therefore clinical signs alone cannot be used to diagnose the condition. Infection with other pathogens such as Borrelia burgdorferi, Babesia caballi, Theileria equi, equine herpes virus, equine infectious anaemia virus and equine arteritis virus can all cause similar clinical signs.
Your vet will need to take some blood samples to test in the laboratory, as well as taking a skin biopsy and looking at any ticks that may be found on your horse.
Most horses recover spontaneously after infection, but antibiotics may be necessary; these may be given orally (by mouth) or intravenously (injected into a vein). Anti-inflammatories may also be prescribed to improve your horse’s comfort and help with appetite.
Occasionally, horses develop this disease again after treatment has finished and may require treatment for a longer period of time with a different antibiotic. Once the infection has resolved, horses are often immune to this disease for a few years.
Tick control is the best method of prevention!
Ensure quick removal of attached ticks and avoid keeping your horse in areas with high tick burdens, such as bushes and overhanging tree branches, and maintain a short pasture.
In addition, the use of tick repellents that contain the drug permethrin can be useful.