TRANSMISSION AND PASSAGE IN HORSES OF THE AGENT OF HUMAN GRANULOCYTICEHRLICHIOSIS

The human granulocytotropic ehrlichia and Ehrlichia equi produce simil ar diseases in their respective host species (humans, horses). Current ly, the phylogenetic and biologic relationships of these 2 uncultured pathogens remain unclear. Previous studies have revealed nucleotide se quence similarity approaching identity at the level of the 16S ribosom al RNA gene. To investigate the biologic similarities of these 2 ehrli chiae, the susceptibility of horses to the human agent was tested by i ntravenous inoculation of infected human blood, The results demonstrat e that the human granulocytotropic ehrlichia produces a disease in the horse indistinguishable from that caused by E. equi, providing biolog ic evidence that these 2 organisms are highly related and potentially conspecific, It is possible that cases of human illness now attributed to human granulocytotropic ehrlichia may in fact be caused by 1 or mo re strains of an ehrlichia known chiefly as an equine pathogen.