Canine Rocky Mountain spotted fever: a kennel epizootic

Abstract

Within a period of 5 consecutive days after the initial observation of illness was made, 7 of 12 Siberian Husky dogs developed clinical signs of Rickettsia rickettsii infection. One dog died and was necropsied. Clinical signs of infection consisted of lethargy, anorexia, ocular and nasal discharges, and neurologic disorder (incoordination and rolling). Scleral blood vessel injection, fever, lymphadenomegaly, splenomegaly, and increased bronchovesicular lung sounds were prominent findings. Clinical laboratory test results identified decreased platelet numbers, variable neutrophil counts, increased serum alkaline phosphatase activity, hyponatremia, hypokalemia, and bilirubinuria. Diagnosis of Rocky Mountain spotted fever was confirmed by serologic evaluation of acute and convalescent sera, using the micro-immunofluorescence technique, and R rickettsii antigen was determined by demonstration of intracellular rickettsial organisms in vascular endothelial cells of brain and lung (stained with carbol-basic fuchsin and aqueous malachite green) and by demonstration of spotted fever-group rickettsiae in tissues by direct fluorescent antibody technique. Near-simultaneous naturally occurring tick-borne infection of 7 dogs with R rickettsii documents an unreported occurrence.