Anaplasmosis is an infectious disease caused by the bacteria Anaplasma phagocytophilum. It is primarily transmitted to humans and animals through the bite of an infected tick, most commonly the black-legged tick (also known as the deer tick) in the United States. Anaplasmosis can affect both humans and animals, but it is primarily a disease of domestic and wild animals, such as cattle, horses, and deer.
Although tick exposure can happen at any time of the year, tick density is highest in the warmer months. Anaplasmosis is more common in certain regions of the United States, including the Northeast, Midwest, and Pacific Coast. Anaplasmosis is a reportable disease, meaning healthcare providers and laboratories are required to report cases to public health authorities.