Rickettsia in Texas

Abstract

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.

Rickettsioses as paradigms of new or emerging infectious diseases

“…Recent studies reveal that only a small proportion of ticks are infected by rickettsiae in the United States, and of these many are R. bellii, with only a small percentage containing R. rickettsii (46,77,150,153,165,187,194). In North Carolina, the state with the highest incidence of RMSF, only 3.4% of D. variabilis ticks contained SFG rickettsiae.…”

Epidemiology of rickettsial diseases

“…Recent studies reveal that only a small proportion of ticks are infected by rickettsiae, many of these are R. bellii, which is not a member of the SFG, and a minute proportion of ticks contain virulent R. rickettsii (8,19,47,50,55,(63)(64)(65) In a large study of rickettsiae in ticks in Ohio, more than 97% of D. variabilis contained no rickettsiae, 2.2% were infected with R. bellii, and only 0.2% contained SFG rickettsiae. Recent studies reveal that only a small proportion of ticks are infected by rickettsiae, many of these are R. bellii, which is not a member of the SFG, and a minute proportion of ticks contain virulent R. rickettsii (8,19,47,50,55,(63)(64)(65) In a large study of rickettsiae in ticks in Ohio, more than 97% of D. variabilis contained no rickettsiae, 2.2% were infected with R. bellii, and only 0.2% contained SFG rickettsiae.…”

Evidence of spotted fever group rickettsiae in state of Rio de Janeiro, Brazil

“…In spite of this, a similar finding was observed by MAGNARELLI et al (1981) 26 in Connecticut. Beside this, various studies on infection in ticks display wide variation, with prevalences ranging from 0.14% to 13.5% 4,6,11,13,18,24,41,44 .…”