Molecular characterization of Rickettsia rickettsii infecting dogs and people in North Carolina.

ABSTRACT

Rocky Mountain spotted fever (RMST) is an important cause of morbidity and mortality in people and dogs in the United States. Disease manifestations are strikingly similar in both species, and illness in dogs can precede illness in people. R. rickettsii has been identified as a Select Agent by the CDC as a Category C priority pathogen by the National Institute of Allergic and Infectious Diseases because it is amenable to use as a bioterror agent. The clinical and temporal relationship of naturally occurring diseases in dogs and people suggests that dogs could serve as sentinels for natural infection and bioterrorist attacks using this organism. Recognizing genetic modifications in naturally occurring disease agents in order to distinguish them from intentionally released agents are priorities put forth by the NIAID. To determine whether the rickettsiae naturally infecting dogs is the same as those that infect persons in a given geographical region, we characterized rickettsial isolates obtained from three dogs and two persons diagnosed with RMSF in North Carolina. Portions of three genes (ompA, rrs, and gltA) amplified by PCR were cloned and sequenced or directly sequenced. Reactions were run in duplicate in forward and reverse directions. Gene sequences were aligned with known sequences deposited in GenBank and with each other. Sequences of the 5' region of the ompA gene were 100% homologous with a tick strain (Bitterroot) of R. rickettsii for all five isolates. Sequences of the rrs gene were 99.8 99.9% homologous with a tick strain (Sawtooth) of R. rickettsii. rrs gene sequences from one dog and the two persons was identical. Sequences of one dog isolate differed from these by one base pair. Sequences from another dog isolate differed by two base pairs. Sequences of the gltA gene are pending. This confirms on a molecular level that R. rickettsii causing naturally occurring RMSF in dogs in North Carolina is highly homologous to R. rickettsii that causes the disease in people in the same region. Sequence data will be deposited in GenBank, thereby providing genetic information regarding naturally occurring R. rickettsii.