Isolation of Typhus Rickettsia from Rat Mites During Epidemic in an Orphanage

Abstract

Macxy 1 predicted that rat and mouse may be the reservoirs and tick, mite, or flea may be the transmitters of typhus fever in the southern parts of the United States. This prediction had been satisfactorily fulfilled except for the possibility of mites as vectors. 1 , 2 , 3 , 4 , 5 While Shelmire and Dove 6 , 7 and Kodama and Kano 8 have experimentally transmitted typhus Rickettsia in laboratory animals by rat mite, no special attention was attached to this vector as an important carrier of typhus Rickettsia. In this communication, we wish to present a first instance of isolation of typhus Rickettsia from mites naturally infected and to discuss briefly its possible epidemiological significance.

A rat trapped in July, 1940, at the end of a typhus epidemic which has occurred in an orphanage was found to harbor 3 mites identified as Liponyssus bacoti. From them, a strain of typhus Rickettsia was established in guinea pig and white rat according to the following criteria: Fever in guinea pig and albino rat, positive Weil-Felix reaction in most of the inoculated rats, in some cases as high a titer as 1:320, recovery of Rickettsiæ on direct examination and cultivation of the tunica vaginalis of infected guinea pig, and finally, positive cross-immunity with a known strain of murine typhus. A second group of rat mites from the same orphanage 4 months after the epidemic showed suggestive findings on inoculation into albino rats but was not further studied. Material from the rat which harbored the first group of mites produced a suggestive typhus infection on inoculation into albino rats.

Comment. The prediction of Macxy that the mite may be a vector of typhus fever has been further supported by the isolation of a strain of typhus Rickettsia from naturally infected mites during an epidemic.