TRANSMISSION OF SCRUB TYPHUS TO HUMAN VOLUNTEERS BY LABORATORY-REARED CHIGGERS

Abstract
Laboratory-reared,Rickettsia tsutsugamushi-infected Leptotrombidium arenicola and L. fletcheri chiggers were fed on 1 and 2 human volunteers, respectively. All subjects developed typical clinical signs and symptoms of scrub typhus beginning on days 8-10 post chigger attachment (PCA); these included fever, severe headache, myalgia, regional lymphadenopathy and eschar. The 2 L. fletcheri subjects developed a transient generalized rash on days 3-4 after the onset of fever; these 2 individuals also appeared to suffer a more severe clinical disease. Rickettsemias were detected in all 3 volunteers beginning on day 7 PCA, 1-3 days, before the onset of clinical disease. Rises in indirect fluorescent antibody titers occurred starting on days 13-19 PCA (day 4-11 post fever) and in Weil-Felix OXK titers starting on days 16-22 PCA (days 7-14 post fever). Thus, the use of laboratory-reared chiggers evidently is a reliable means of transmitting scrub typhus infections to volunteers.