EVALUATION OF THE PATHOGENIC POTENTIAL OF RICKETTSIA-CANADA AND RICKETTSIA-PROWAZEKII ORGANISMS IN DOGS

An unusual pattern of seroreactivity to antigens of rickettsial organi sms (Rickettsia rickettsii, R rhipicephali, R montana, and R bellii), particularly to R bellii antigen, was detected in 3 dogs during a 2-mo nth period. Thus, studies were initiated to clarify the pathogenic pot ential of the move distantly related rickettsial organisms (R canada a nd R prowazekii) in dogs. Because R bellii ave nonpathogenic richettsi ae that shave numerous common properties with spotted fever group and typhus-group rickettsiae, and because closely related pathogenic relat ives of R bellii have not been identified, we examined the pathogenic potential of these typhus-group richettsiae by resting stored serum sa mples, by attempting rickettsial isolation from febrile dogs, and by e xperimentally inoculating dogs with R canada and R prowazekii. Evaluat ion of results of a serosurvey of acute and convalescent serum samples from 80 dogs in which Rocky Mountain spotted fever had been considere d as a differential diagnosis, but seroconversion to R rickettsii had not been documented identified 1 dog with a fourfold increase in antib ody titer to R rhipicephali and 3 dogs with fourfold increases in anti body titer to 1 or move antigens of typhus-group rickettsial organisms . A study of 15 dogs that were febrile during summer months failed to identify serologic or tissue culture evidence of typhus-group ricketts ial infection or typhus-group, rickettsemia, but did result in isolati on of R rickettsii and Ehrlichia canis, respectively,from 1 dog each. In our final study, after experimentally inoculating 6 dogs with R can ada and R prowazekii, all dogs seroconverted to the respective richett siae, but rickettsemia or clinical and hematologic evidence of disease was not observed. Collectively, our results did not provide convincin g evidence to support a pathogenic role for R canada and R prowazekii organisms in dogs. Our findings supported the conclusion that an unide ntified microorganism, which results in production of antibodies again st R bellii and antigens of typhus-group rickettsial organisms, contri buted to an unexplained febrile illness of dogs in the southeastern Un ited States. In an effort to identify, dogs in which serologic evidenc e supports this conclusion, we recommend the use of selected spotted f ever-group, typhus-guoup, and R bellii antigens for serodiagnostic pur poses. We also recommend that diagnosticians attempt tissue culturing to isolate organisms when a rickettsial agent is suspected.