Progress in the study of Ehrlichia chaffeensis and human monocytic ehrlichiosis.

Ehrlichia chaffeensis is a coccal,gram-negative,zoonotic,pathogenic bacterium.It is obligately intracellular and cycles mainly through the tick-deer cycle.It can infect humans and cause human monocytic ehrlichiosis.E.chaffeensis is transmitted primarily by the lone star tick,or Amblyomma americanum,and is maintained in nature by persistent infection of the white-tailed deer.Ticks acquire E.chaffeensis infection by feeding on infected deer,maintain the infection transtadially as the tick molts from stage to stage,and then infect other susceptible mammalian hosts.E.chaffeensis infection was first discovered in 1986.Its main symptoms are fever and headache,and presenting patients have a mild to severe illness.Knowledge of this pathogen is extremely scant.It is hard to culture,so it is difficult both to diagnose and research.This review has summarized the progress of the study of E.chaffeensis and human monocytic ehrlichiosis in terms of its etiology,epidemiology,clinical manifestations,diagnosis,treatment and prevention.