Two Cases of Spotted Fever Group Rickettsiosis Contracted in Southern Parts of Africa

A 40-year-old Japanese male stayed in Zimbabwe and developed a fever above 38 degrees C during which he noted a typical eschar in the lumbar region and also regional inguinal lymphadenopathy. Although not conspicuous, erythematous eruptions accompanied by itching were observed on the face, trunk and lower extremities. After returning to Japan and visiting our hospital, he was suspected of rickettsiosis and put on minocycline which gradually led to the improvement of the symptoms. Immunofluorescence antibody determinations disclosed rising titers against Rickettsia conorii (R. conorii) for both IgM and IgG classes. The second patient, a 34-year-old Japanese male, developed fever, generalized erythema and a typical eschar while staying in South Africa. The first blood sample showed positive IgM and IgG antibodies against R. conorii, and the second sample a decline in IgM but not in IgG class antibodies. Both cases were diagnosed as spotted fever group rickettsiosis based on their clinical manifestations including typical eschar and also the results of antibody determinations. Most of the previous cases of spotted fever group rickettsiosis in Africa have been regarded as Mediterranean spotted fever which is caused by R. conorii and transmitted by Rhipicephalus sanguineus. However, recently, the presence of another type of spotted fever group rickettsiosis, African tick-bite fever, caused by Rickettsia africae and transmitted by Amblyomma hebraeum has been proposed. Although clinical features of the two rickettsiosis are reported to be separable, apparent cross reaction between the two organisms hampers the use of conventional antibody determinations for their differentiation. For the two cases presented here identification of the causative rickettsia species was impossible, because they were not isolated. With ever increasing numbers of international travel, physicians should be alert to the possibility of spotted fever group rickettsiosis when encountering febrile patients returning from endemic countries. This is particularly important considering that beta-lactam antibiotics commonly used as an empiric therapy are not effective, and the disease has a potential to develop into severe forms.