Last Updated on March 29, 2022 by Allison Price
Anaplasmosis, also known as equine-granulocytic ehrlichiosis, is a seasonal infectious disease that’s most common in the United States. Although most cases are found in California, cases have also been reported in other states such as Connecticut, Illinois and Arkansas. There have been cases confirmed in South America, Britain, Sweden, Great Britain and British Columbia. California’s seasonal disease, which occurs in late fall, winter and spring, is called “Seasonal Disease”.
The rickettsial agent Anplasma phagocytophilum is responsible for this disease. It is found in the bloodstream following tick bite transmission. At this point, the risk of transmitting the disease to humans is unknown. Horses and humans appear to have the same strain of the agent. However, tick bites may be the cause for infection.
The severity of the signs depends on the animal’s age and the duration of the illness. Some signs may not be apparent. Horses younger than one year may only have a fever; horses older than three years can develop mild depression, mild limb swelling and poor coordination. Adults can show the typical signs of fever: poor appetite, depression and limb swelling. Fever usually occurs within the first 3 to 7 days after infection. However, it can last up to 6 to 12 consecutive days. Over several days, symptoms can become more severe. An existing infection, such as a respiratory infection or a leg wound, can make the situation worse. White blood cells can detect the infectious agent within 3-5 days. The disease can also be detected using DNA and antibody tests.
It is easy to treat the disease in its early stages with appropriate antibiotics. Although the severity of the disease can vary, many horses are able to recover within 14 days with no treatment. Rare fatalities due to secondary infections have been reported. Injectable corticosteroids may be beneficial for horses with neurologic or severe signs. Horses that have been treated for the disease are able to develop immunity for at most 2 years. They also do not become carriers. To control the disease, tick control measures must be taken. There is no vaccine.