Rocky Mountain Spotted Fever (RMSF) should be high on the differential list for any dog that shows general signs of illness accompanied by a history of tick bites, especially between late March and late September. The veterinarian will take a complete history of the dog’s medical background and will perform a thorough physical examination. This initial data base usually will also include routine blood work (a complete blood count [CBC] and a serum biochemistry profile), together with a urinalysis. Dogs with RMSF often have low blood platelet levels, mild anemia (low red blood cell numbers) and slightly low white blood cell levels (leukopenia), especially early in the course of the infection. As the disease progresses, white blood cell numbers tend to increase. Cholesterol levels are almost always elevated in dogs with Rocky Mountain Spotted Fever. The reason for this association still remains a mystery. The urinalysis of affected dogs usually discloses protein and blood in the urine.
The diagnosis of Rocky Mountain Spotted Fever can be confirmed by specialized blood tests that detect antibodies to Rickettsia rickettsii, which is the infectious microorganism that causes this disease. These advanced diagnostic techniques require sending blood samples to a specialized veterinary pathology laboratory. These tests should be done at the time the dog presents with signs of illness, and then repeated several weeks later. Biopsies of affected tissues or organs can also be taken and submitted to a diagnostic laboratory. Tissues or blood can be cultured, although this is not commonly done and requires a high biosafety-level laboratory. The dog’s attending veterinarian can explain these tests and other diagnostic protocols to the owner in greater detail.
Rocky Mountain Spotted Fever can be virtually indistinguishable from infection with Ehrlichia canis, which is transmitted by the brown dog tick, Rhipicephalus sanguineus. RMSF and ehrlichiosis can be differentiated by specialized tests, called serology, done on blood samples.