Experimental Infection Models of Ticks of theRhipicephalus sanguineusGroup withRickettsia conorii

Abstract

Rhipicephalus sanguineus group ticks collected on dogs in Thailand were maintained in the laboratory over several generations to test methods to infect these ticks with Rickettsia conorii, the agent of Mediterranean spotted fever. Three methods were tested: (1) infection of adults and nymphs through artificially induced bacteremic rabbit, (2) capillary feeding of solution containing 5 x 10(3) and 5 x 10(5)pfu/mL of R. conorii to adult female ticks, and (3) immersion of engorged nymphs which were "one leg-cut," "two leg-cut," or "cuticle cut" in solution containing R. conorii. The most efficient method to infect adult ticks with R. conorii was infection of ticks through the bacteremic rabbit (71.4%). The best method to infect nymphs with R. conorii was immersion of "one leg-cut" engorged nymphs in solution containing R. conorii (30%). Interestingly, a high mortality of the ticks infected with R. conorii was observed regardless of the method used. The harmful effect of R. conorii on Rh. sanguineus group ticks from Thailand is discussed including the role of the geographic origin of the ticks and the difficulties to identify ticks within this group to the species level.