Comparative Evaluation of Infected and NoninfectedAmblyomma tristeTicks withRickettsia parkeri, the Agent of an Emerging Rickettsiosis in the New World
The distribution ofRickettsia parkeriin South America has been associated withAmblyomma tristeticks. The present study evaluated under laboratory conditions two colonies ofA. triste: one started from engorged females that were naturally infected byR. parkeri(designated as infected group); the other started from noninfected females (designated as control group). Both colonies were reared in parallel for five consecutive generations. Tick-naïve domestic rabbits were used for feeding of each tick stage and generation.R. parkeriwas preserved by transstadial maintenance and transovarial transmission inA. tristeticks for five consecutive generations, because all tested larvae, nymphs, and adults from the infected group were shown by PCR to contain rickettsial DNA. All rabbits infested by larvae, nymphs, and adults from the infected group seroconverted, indicating that these tick stages were all vector competent forR. parkeri. Expressive differences in mortality rates were observed between engorged nymphs from the infected and control groups, as indicated by 65.9% and 92.4% molting success, respectively. Our results indicate thatA. tristecan act as a natural reservoir forR. parkeri. However, due to deleterious effect caused byR. parkerion engorged nymphs, amplifier vertebrate hosts might be necessary for natural long-term maintenance ofR. parkeriinA. triste.