Louse-borne or epidemic typhus

The epidemiological cycle of louse-borne typhus has been described in the section on this disease in Europe. The last louse-borne outbreak of the disease in the USA was in 1921 but sporadic cases of Rickettsia prowazekii are still reported. Between January 1976 and January 1979 serum specimens from 1575 individuals were received at the US Centers for Disease Control and tested for antibodies to rickettsiae. Of these, sera from 8 persons gave serological results indicative of recent infections with epidemic typhus rickettsiae. Five of the persons were from Georgia, and one each was from Tennessee, Pennsylvania and Massachusetts. The illnesses occurred during the winter, chiefly in persons living in a rural environment. The clinical picture was compatible with louse-borne epidemic typhus. There was no apparent contact with human body or head lice among the patients, and no cases occurred in patient contacts, indicating that infection was not associated with the classic man–louse–man cycle of epidemic typhus. Two of the eight patients had contact with flying squirrels (Glaucomys volans) suggesting that they became infected from this known non-human reservoir host of R. prowazekii (McDade et al., 1980). Thus the infection is now known to exist as a zoonosis of flying squirrels in the USA. There have been 33 human infections diagnosed between 1976 and 1984; none of the cases has died. Most of the patients have either handled squirrels or squirrels have been present in the patient's home.