Report cases RMSF in US 2013/CDC
Three ticks can carry the RMSF bacterium, Rickettsia rickettsii, in the United States (US):
- Dermacentor variabilis (dog tick)
- Dermacentor andersoni (wood tick)
- Amblyomma americanum (lone star tick)
The lone star tick, typically found throughout the southeastern, eastern, and south-central states, has been expanding its range north and west over the last few decades. Although it can transmit RMSF, it should be noted that the lone star tick is not as likely to transmit the disease as the dog or wood tick.
The annual incidence goes up and down over the years (refer to the chart on the right), but mortality has decreased from 28% in 1940 to less than one percent in 2008. RMSF is the most common rickettsial disease in the US, with about 250-2,500 cases per year. Most cases occur from April to September when the tick vectors are active in nature. The number of infected persons increases as patients age, until age 65-70, where it falls slightly. Most cases are seen East of the Rocky Mountains, with most cases reported in North Carolina in a band across Tennessee, Missouri, Arkansas, and Oklahoma.