Maintenance of the infection byRickettsia amblyommatisinAmblyomma cajennensesensu stricto ticks and evaluation of vector competence

Rickettsia amblyommatishas been reported infecting various tick species throughout the western hemisphere, includingAmblyomma cajennensesensu stricto (s.s.). The present study aimed to evaluate whetherR. amblyommatiscan be maintained by transovarial transmission and transstadial passage inA. cajennenses.s. ticks, and whether these ticks are competent vectors of this rickettsial agent. We selected engorged females that were naturally infected or uninfected byR. amblyommatis, and reared their offspring (infected and control groups, respectively). Immature ticks were allowed to feed on guinea pigs, whereas adults fed on rabbits. All stages and individuals of each generation of the infected group yielded rickettsial DNA, which was not detected in any tick from the control group. No host from the control group seroconverted toR. amblyommatis. Among 16 guinea pigs and eight rabbits infested withR. amblyommatis-infected ticks, only one guinea pig seroconverted toR. amblyommatis. Some unfed adult ticks of the infected group were dissected, and DNA was extracted from their salivary glands and from their carcasses. DNA ofR. amblyommatiswas detected in all carcasses, but not in the salivary glands. Results of this study indicate very low vector competence ofA. cajennenses.s. forR. amblyommatis. Previous studies reported domestic animals with high titers toR. amblyommatisin areas where these animals are naturally infested chiefly byA. cajennenses.s. ticks. One may consider that the vector competence ofA. cajennenses.s. forR. amblyommatiscould vary among tick populations and/or rickettsial strains.