Anaplasmosis encephalitis and infection of non-myeloid bone marrow precursors.

Due to climate change, infections from tickborne pathogens are becoming more prevalent in the Northern Hemisphere. Human granulocytic anaplasmosis, caused by the obligate intracellular gram-negative bacteria Anaplasma phagocytophilum and carried by Ixodes ticks, can lead to morbidity and mortality in select populations. Anaplasmosis is commonly accompanied by significant cytopaenia, the pathophysiology of which remains unknown. Our case report describes an uncommon meningoencephalitic presentation of anaplasmosis with substantial anaemia and thrombocytopaenia. Additionally, we propose a mechanism of bone marrow infection and suppression by A. phagocytophilum which may be responsible for the cytopaenia in anaplasmosis and provide pictographic evidence of anaplasma in peripheral blood, cerebrospinal fluid and bone marrow.