Canine Rocky Mountain spotted fever: A retrospective study of 30 cases

Rocky Mountain spotted fever (RMSF) was diagnosed in 30 dogs examined at No rth Carolina State University, Veterinary Teaching Hospital between 1984 an d 1997. Historical, physical examination, and laboratory abnormalities were reviewed. Diagnostic criteria included a four-fold rise in antibody titer to Rickettsia rickettsii (R. rickettsii) (n=15) or a single R. rickettsii a ntibody titer of 1:1024 or greater (n=15; when this initial titer was deter mined one week or more after the onset of clinical signs). Fifteen (50%) dogs were greater than seven years of age, and 13 (43%) dogs were between two and seven years of age. There was no sex predilection. Onl y five (17%) dogs had a history of known tick exposure. Presumably due to d elayed diagnosis, dogs with antibody titers of 1:1024 or greater at the tim e of presentation had a higher incidence of more severe neurological dysfun ction (e.g., ataxia, hyperesthesia, vestibular disease, and seizures) and c utaneous lesions (e.g., hyperemia, edema, petechiae, ecchymoses, and necros is). Laboratory findings included anemia, leukocytosis accompanied by toxic granulation of neutrophils, hypoalbuminemia, and coagulation abnormalities ; signs were generally more severe in the 15 dogs with R. rickettsii antibo dy titers of 1:1024 or greater at the time of presentation. Twelve (40%) do gs in this study were severely thrombocytopenic (less than 75 x 10(3) plate lets/mul; reference range, 200 to 450 x 10(3)/mul), without clinical eviden ce of fulminant disseminated intravascular coagulation. In this study, the survival rate following R. rickettsii infection was 100%.