Abstract
Rocky Mountain spotted fever is endemic to the São Paulo metropolitan area, Brazil, where the etiologic agent, Rickettsia rickettsii, is transmitted to humans by adult Amblyomma aureolatum ticks. We determined the minimal feeding period required by A. aureolatum nymphs and adults to transmit R. rickettsii to guinea pigs. Unfed nymphs and unfed adult ticks had to be attached to the host for >10 hours to transmit R. rickettsii. In contrast, fed ticks needed a minimum of 10 minutes of attachment to transmit R. rickettsii to hosts. Most confirmed infections of Rocky Mountain spotted fever in humans in the São Paulo metropolitan area have been associated with contact with domestic dogs, the main host of A. aureolatum adult ticks. The typical expectation that transmission of tickborne bacteria to humans as well as to dogs requires ≥2 hours of tick attachment may discourage persons from immediately removing them and result in transmission of this lethal bacterium.
Highlights
Rocky Mountain spotted fever is endemic to the São Paulo metropolitan area, Brazil, where the etiologic agent, Rickettsia rickettsii, is transmitted to humans by adult Amblyomma aureolatum ticks
All PCRs performed on the DNA of nymphal and adult ticks that fed on guinea pigs for different periods resulted in amplicons compatible with R. rickettsii, indicating that all 90 guinea pigs in this study were exposed to R. rickettsii–infected ticks
The >10-hour feeding period observed for unfed ticks is similar to the 10-hour period previously reported for D. andersoni ticks in 2 earlier studies [13,14]; albeit much lower than the periods previously reported for D. andersoni (>48 hours) in another study [10] and for A. cajennense ticks (36 hours) in Brazil [15]
Summary
Rocky Mountain spotted fever is endemic to the São Paulo metropolitan area, Brazil, where the etiologic agent, Rickettsia rickettsii, is transmitted to humans by adult Amblyomma aureolatum ticks. Most confirmed infections of Rocky Mountain spotted fever in humans in the São Paulo metropolitan area have been associated with contact with domestic dogs, the main host of A. aureolatum adult ticks. A recent study demonstrated that the expression of some R. rickettsii genes is modulated by the physiologic state of the host, such as a fasting or feeding A. aureolatum tick [12]; specific genes responsible for rickettsial reactivation remain unknown
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