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ANAPLASMOSIS: IMPORTANT FACTS
Jennifer Lowry, DVM
Anaplasmosis is a tickborne disease caused by the bacterium Anaplasma phagocytophilum (formerly called Ehrlichia equi.)
Presenting signs can include a sudden onset of the following: fever (102-105), depression, decreased appetite, swollen legs, weakness, and reluctance to walk.
Fever is highest during the first three days, and can persist for up to 9-12 days if the disease is not treated.
The disease occurs in late fall, winter, and spring. (This is in contrast to Potomac Horse Fever, which presents with similar signs but occurs in mid-summer to early fall).
The incubation period (time after tick bite before clinical signs) is usually 1-9 days, but has been demonstrated to be as long as 25 days. Severity of signs varies with age and duration of infection. In young horses, signs are often mild and are not noticed, while older horses tend to be more severely affected.
Recovered horses will have a natural immunity for at least two years and are not carriers.
A CBC will often indicate several abnormalities that are seen with this disease: low white blood cells, low red blood cells (anemia), and low platelets. An Anaplasma-specific blood test (PCR) will provide a definitive positive or negative result. Often the same tick that carries Anaplasma also carries Lyme Disease, so your vet may recommend testing for both.
Tetracycline (given IV) and Doxycycline (given orally) are very effective in treating Anaplasmosis. Fever and other presenting signs resolve quickly, within 24-48 hours of treatment.
The disease is usually not fatal if there are no secondary complications. When Anaplasmosis is diagnosed in the early stage of infection and treated properly, the prognosis for return to previous level of health and exercise is excellent.