Spotted fever group of Rickettsiae Infection
Spotted fever group
The several species of tick-borne spotted fever group rickettsias are transmitted by the bite of various species of ticks. The infection is maintained transovarially or through a tick-mammal-tick cycle. Rocky mountain spotted fever (RMSF) is a dangerous acute infectious disease of the Western hemisphere caused by R. rickettsii and is transmitted by various species of ticks. Its clinical manifestations are similar to that of typhus and scrub typhus. However, its incubation period is shorter (7 to 7 days). The rash usually begins in the extremities and then involves the trunk. The disease will respond favorably to early antibiotic treatment. However, in sever cases, mycocarditis, DIC, and other physiological derangements may develop leading to death. The mortality rate is 5%. Because the disease may present as an undifferentiated fever, therapy should be started on a presumptive diagnosis based on the history of tick bites or potential exposure in an endemic area. An early presumptive diagnosis may be verified by finding the organisms in skin punch biopsy sections stained with specific fluorescent Ab.
R. conorii infections occur under numerous local names e.g. botenneuse fever, Meditteraena spotted fever, Kenya tick typhus, Indian tick typhus etc. are widely distributed in S. Europe, Africa, and Asia. The disease resembles RMSF with some differences. There is often ulcerated primary lesion (eschar) at the site of the infected tick bite. The rash tends to be more nodular and the disease milder. It responds readily to anti-rickettsial antibiotics
Scrub typhus is an acute typhus-like disease of Asia caused by multiple serotypes of R. tsutsugamushi. It is transmitted by the bite of the larvae (chiggers) of certain mites. Primary scrub typhus resembles louse-borne typhus in many ways. However, an eschar frequently develops at the site of the inoculation. Response to chemotherapy is rapid. The mortality of the disease ranges from the very low to very high.