Granulocytic anaplasmosis — emerging tick-borne disease of humans and animals

Granulocytic anaplasmoses represent a group of emerging tick-borne infectious diseases caused by the obligate intracellular gram-negative bacterium, Anaplasma phagocytophilum (Rickettsiales) that infects granulocytes. It has been known as a ruminant pathogen in Europe since 1932, however, recently it has emerged as a pathogen of humans and domestic animals such as dogs and horses in the Northern Hemisphere, including United States and Europe. Rodents and game animals (especially deer) are presumed to play a crucial role in the maintenance of A. phagocytophilum in natural foci and serve as competent reservoirs. Up to now, the presence of bacterial DNA has been confirmed by molecular methods in a number of domestic and wildlife animals. Circulation of several genotypes has been confirmed in natural foci but the vector competence and the host spectrum involved in its circulation is still under investigation. Human granulocytic anaplasmosis (HGA) typically occurs in spring or summer and clinical manifestations range from mild or self-limiting to severe disease, especially in elderly patients with up to 50% requiring hospitalization and 7% intensive care. So far, no confirmed A. phagocytophilum infections of humans have been reported in Slovakia despite the fact that the presence of anti-anaplasma antibodies has been detected in investigated patients sera. This fact could be explained by non-specific clinical signs of the infection or lack of information in physicians and underdiagnosed or misdiagnosed cases. The purpose of this review is to present biology, ecology and life cycle of A. phagocytophilum and introduce clinical symptoms, diagnosis and treatment of the infection caused by this pathogenic bacterium.