Rocky Mountain Spotted Fever

Infection due to Rickettsia rickettsii affects blood vessels throughout the body. The myocardium, as in this case, shows a mononuclear cell infiltration. Grossly, petechial hemorrhages are usually present. In this photo RBCs have extravasated into the interstitium and myocyte dropout is apparent.

Rocky mountain spotted fever is a tick-borne disease caused by a gram negative coccobacillus, Rickettsia rickettsii. After entering the body via a tick bite, the organism spreads throughout the body via blood and lymphatics. It has a propensity to invade endothelial cells causing vascular injury in many organs including lungs, heart, brain, skin, and kidneys. If untreated about 1 in 4 patients die. The mortality is greater in the elderly. Fever and bradycardia are prominent presenting features. A petechial rash is also likely but it may not appear until later. Despite the name, the disease has its highest US incidence in North Carolina and Oklahoma.

From the slide collection of the late Dr. Charles Kuhn