The bacterium first resides in an early endosome, where it acquires nutrients for binary fission and grows into small groups called morulae.

This disease was first identified due to a Wisconsin patient who died with a severe febrile illness two weeks after a tick bite.

Other symptoms include fever, headache, absence of skin rash, leucopenia, thrombocytopenia, and mild injury to the liver.

[3] A. phagocytophilum binds to fucosylated and sialylated scaffold proteins on neutrophil and granulocyte surfaces.

A type IV secretion apparatus is known to help in the transfer of molecules between the bacterium and the host.

It can survive the first encounter with the host cell by detoxifying superoxide produced by neutrophil phagocyte oxidase assembly.

It also disrupts normal neutrophil function, such as endothelial cell adhesion, transmigration, motility, degranulation, respiratory burst, and phagocytosis.

In general, patients with symptoms of HGA and unexplained fever after a tick exposure should receive empiric doxycycline therapy while their diagnostic tests are pending, especially if they experience leukopenia and/or thrombocytopenia.