Human Granulocytic Anaplasmosis - Ecology and Epidemiology

Ecology and Epidemiology

A. phagocytophilum is transmitted to humans by the Ixodes persulcatus group of ticks. These ticks are found in the US, Europe, and Asia. In the US, I. scapularis is the tick vector in the East and Midwest states, and I. pacificus in the Pacific Northwest. According to the CDC, the 2008 prevalence rate in the United States was 2.4 per million (most of the cases were in people over 40 years old), with a fatality rate of less than 1%

The major mammalian reservoir for A. phagocytophilum in the eastern United States is the white-footed mouse, Peromyscus leucopus. Although white-tailed deer harbor A. phagocytophilum, evidence suggests that they are not a reservoir for the strains that cause HGA.

Anaplasma phagocytophilum shares its tick vector with other human pathogens, and about 10% of patients with HGA show serologic evidence of coinfection with Lyme disease, babesiosis, or tick-borne meningoencephalitis.