Anaplasmosis in humans

Introduction Changes in ecology wrought by human behavior have had a substantial effect on the environment (1). One such effect, evident to those interested in infectious diseases has been the increase in zoonoses, particularly vector-transmitted infections (2,3). Unanticipated changes occurring with human environmental modifications have led to the concurrence of several important events: increases in the abundance of some wild animal populations owing to the loss of natural predators or adaptation to peridomestic environments, a consequent increase and spread of ectoparasites, such as ticks, associated with these wild animal populations, and the human desire to live, work, or recreate in natural, wild, or otherwise “pristine” habitats for which humans are nonnatural inhabitants. Such is the case with the emergence and reemergence of important tick-transmitted infections such as Lyme disease, but also the more deadly rickettsial pathogens, including one not previously recognized in humans now assigned to the genus Anaplasma. The purpose of this chapter is to describe various features of the clinical and pathologic aspects of human disease, and important related components of ecology and epidemiology, recognized to occur with infection by Anaplasma phagocytophilum, the sole member of the genus known to infect and cause disease in humans.