Severe anaplasmosis represents a treatable cause of secondary hemophagocytic lymphohistiocytosis: Two cases and review of literature.

Anaplasmosis is an emerging infection in the United States and remains under-recognized in many areas including Pennsylvania. Presenting signs and symptoms are often nonspecific, but fulminant infection can occur in vulnerable populations. We present two cases of severe anaplasmosis that progressed to secondary hemophagocytic lymphohistiocytosis (HLH). This severe immune dysregulation syndrome has an extremely high mortality, but anaplasmosis represents one of the few treatable underlying etiologies. It is imperative for physicians to recognize this complication and start empiric doxycycline, as early treatment improves mortality. We also present a case of anaplasmosis-induced HLH successfully treated with a combination of doxycycline, steroids, and anakinra (an IL-1 receptor antagonist), highlighting that this primarily immune-mediated complication is amenable to treatment with both antibiotics and immune suppression.