Inclusion appendages associated with the intraerythrocytic rickettsial parasiteAnaplasma marginaleare composed of bundled actin filaments

Anaplasma marginale, a tick-borne rickettsia that infects erythrocytes of cattle, occurs within a parasitophorous vacuole or inclusion body. A tail-like inclusion appendage, composed of multiple filaments, occurs in association with the inclusion body membrane. The composition and function of the inclusion appendage have not been determined. In this study, theA. marginaleinclusion appendage in bovine erythrocytes was found to be composed of actin filaments as determined by labeling with rhodamine-conjugated phalloidin. Electron microscopy studies revealed that theA. marginaleinclusion appendages differed from F-actin tails reported previously in association with other pathogens in eukaryotic cells because these highly ordered structures were organized into regularly occurring striations, and the appendages were adhered directly to the parasitophorous vacuole membrane. In addition, actin appendages have not been described previously in erythrocytes. The potential role of the inclusion appendage associated withA. marginalein bovine erythrocytes and recently fed ticks is discussed.