Rocky Mountain Spotted Fever

Infection with rickettsial organisms such as Rickettsia rickettsii produce a hemorrhagic rash and hemorrhages in many internal organs including the lung (left photo).  The changes are secondary to vasculitis (center photo). The endothelial cells are swollen and there is a mononuclear perivascular innflammation. Mononuclear interstitial pneumonia is seen in the photo on the right.

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