CLINICAL, HEMATOLOGIC, AND HUMORAL IMMUNE-RESPONSE IN FEMALE DOGS INOCULATED WITH RICKETTSIA-RICKETTSII AND RICKETTSIA-MONTANA

  • 1 January 1988
    • journal article
    • research article
    • Vol. 49  (1) , 70-76
Abstract
Female Beagles were inoculated intradermally with a sublethal dose of Rickettsia rickettsii and R. montana. Three dogs (group 1) were inoculated with 2 .times. 102 plaque-forming units (PFU) of R. rickettsia and were treated with tetracycline beginning on postinoculation day (PID) 12; 3 dogs (group 2) were inoculated with 2 .times. 102 PFU of R. rickettsii but were not treated; 3 dogs (group 3) were inoculated with 2 .times. 102 PFU of R. montana. Group-3 dogs failed to seroconvert and were inoculated a second time on PID 68. Groups 1 and 2 dogs inoculated with R. rickettsii became depressed and developed occasional inappetence, fever, hematochezia, and ocular lesions. These dogs had a decrease in PCV and RBC count, and initial decrease in WBC count followed by leukocytosis, and a decrease in platelet count. Group-3 dogs inoculated with R. montana remained healthy. After R. rickettsii inoculation, the serologic response to spotted fever group (SFG) rickettsial antigens (R. rickettsii, R. rhipicephali, R. montana, and R. belli) was similar. The antibody response to R. rickettsii was first detected on PID 9, with peak titers reached by PID 20. Serum titers to R rickettsii remained stable or decreased one dilution through PID 120. Of 4 SFG rickettsial antigens, the highest serologic response was to R. rickettsii. A cross-reacting antibody response with R. rhipicephali and R. montana was nearly identical and was only slightly less than the response to R. rickettsii. Cross-reacting antibodies to R. belli were of lower mean titer and of shorter duration than were cross-reacting antibodies to other SFG rickettsiae. A second inoculation with R. montana resulted in antibody titers to all 4 SFG antigens, with the highest mean antibody titer to R. montana. All 9 dogs were challenge exposed with 2 .times. 102 PFU of R. rickettsii on PID 216. Groups 1 and 2 dogs had mild depression, fever, and ocular lesions. Challenge exposure of group-3 dogs previously inoculated with R. montana resulted in a similar pattern of clinical abnormalities and hematologic alterations, as was observed in groups 1 and 2 dogs inoculated initially with R. rickettsii. The mean titers to all 4 SFG antigens were greater in dogs inoculated with R. montana, than were responses to these antigens after inoculation with R. rickettsii only. Despite antigenic similarity in canine immune recognition to R. rickettsii and R. montana, the use of nonpathogenic R. montana to infer protection against R. rickettsii was not successful.