Experimental infection of the tick Amblyomma cajennense, Cayenne tick, with Rickettsia rickettsii, the agent of Rocky Mountain spotted fever

• Published in: Medical and veterinary entomology Vol. 26; no. 2; pp. 139 - 151
• Main Authors: SOARES, J. F, SOARES, H. S, BARBIERI, A. M, LABRUNA, M. B
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.06.2012; Wiley Subscription Services, Inc
• Subjects: Acari; adults; Amblyomma cajennense; Animals; Arachnid Vectors - microbiology; Arachnid Vectors - physiology; Arachnids; Brazil; Female; females; Fluorescent Antibody Technique, Indirect; Guinea Pigs; Host-Parasite Interactions; Infections; Insect Vectors - microbiology; Insect Vectors - physiology; Ixodidae; Ixodidae - growth & development; Ixodidae - microbiology; Larva - growth & development; Larva - microbiology; larvae; Lyme disease; Male; Nymph - growth & development; Nymph - microbiology; nymphs; Polymerase Chain Reaction; progeny; Rabbits; reproductive performance; Rickettsia rickettsii; Rickettsia rickettsii - physiology; Rocky Mountain spotted fever; Rocky Mountain Spotted Fever - microbiology; Rocky Mountain Spotted Fever - transmission; spotted fever; ticks; transovarial transmission; transstadial transmission; vector competence; Brazil
• ISSN: 0269-283X; 1365-2915
• DOI: 10.1111/j.1365-2915.2011.00982.x

In the laboratory, Amblyomma cajennense (Acari: Ixodidae) (Fabricius) larvae, nymphs and adults were exposed to Rickettsia rickettsii by feeding on needle‐inoculated animals, and thereafter reared on uninfected guinea pigs or rabbits. Regardless of the tick stage that acquired the infection, subsequent tick stages were shown to be infected (confirming transstadial and transovarial transmissions) and were able to transmit R. rickettsii to uninfected animals, as demonstrated by serological and molecular analyses. However, the larval, nymphal and adult stages of A. cajennense were shown to be partially refractory to R. rickettsii infection, as in all cases, only part of the ticks became infected by this agent, after being exposed to rickettsemic animals. In addition, less than 50% of the infected engorged females transmitted rickettsiae transovarially, and when they did so, only part of the offspring became infected, indicating that vertical transmission alone is not enough to maintain R. rickettsii in A. cajennense for multiple generations. Finally, the R. rickettsii‐infected tick groups had lower reproductive performance than the uninfected control group. Our results indicate that A. cajennense have a low efficiency to maintain R. rickettsii for successive generations, as R. rickettsii‐infection rates should decline drastically throughout the successive tick generations.