Transmission of scrub typhus to human volunteers by laboratory-reared chiggers

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 days 8-10 post chigger attachment (PCA); these included fever, severe headache, myalgia, regional lymphadenopathy, and eschar. The two L. fletcheri subjects developed a transient generalized rash on days 3-4 after the onset of fever, and these two individuals also appeared to suffer a more severe clinical disease. Rickettsemias were detected in all three 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 26-22 PCA (days 7-14 post fever). These results strongly suggest that the use of laboratory-reared chiggers is a reliable means of transmitting scrub typhus infections to volunteers.