Rickettsia in Texas.

Since the first reported case in 1941, Rocky Mountain spotted fever in humans has been reported from many areas of Texas, with two major foci, one located in the north-central region and the other in the eastern region of the state. During the period 1979-1988, 421 cases of RMSF were reported, reaching 108 cases in 1983 and declining in subsequent years. Statewide surveillance programs to detect spotted fever group rickettsiae in tick populations were initiated in 1976. In recent years, the SFG infectivity rates in these tick species have included Dermacentor variabilis, 5.2%; Amblyomma americanum, 7.1%; Rhipicephalus sanguineus, 2.9%; and Ixodes scapularis, 10.2%. Further determination of involved rickettsial species and pathogenicity is needed, as many of these specimens are collected from humans and during epidemiological investigations. Various foci of murine typhus occur in Texas. During 1979-1988, 400 human cases were reported. The majority of cases occurred in people who resided in south Texas. Several investigations have shown a possible link between typhus infections and exposure to Ctenocephalides felis. Other rickettsial infections currently reported in Texas include Q fever and ehrlichiosis.