Doctor's Notes on Rocky Mountain Spotted Fever
Rocky Mountain spotted fever (RMSF) is an illness caused by the bacteria Rickettsia rickettsii that is transmitted to humans by an infected tick bite. RMSF is the most common fatal tickborne disease in the U.S.
Early symptoms of Rocky Mountain spotted fever are nonspecific and may be mistaken for other illness so it is important to alert a doctor that a tick bite has occurred. Symptoms and include fever (usually greater than 102 F), chills, nausea, vomiting, headache, muscle pain, and fatigue. About two days to two weeks after the tick bite occurs, symptoms including rash (red spots), abdominal pain, joint pains, and diarrhea develop. The rash usually begins on the wrists and ankles and spreads to the palms and soles of the feet. Other symptoms of Rocky Mountain spotted fever may include loss of appetite, hallucinations, sensitivity to light, eye redness, and excessive thirst. If RMSF is not promptly diagnosed and treated, severe symptoms may develop including low blood platelets that can lead to internal bleeding, low blood sodium, meningismus (neck stiffness, headache, and fever that may indicate brain membrane irritation), confusion, blindness, or coma that can be fatal.
Rocky Mountain Spotted Fever Symptoms
Unfortunately, the early symptoms of RMSF are nonspecific, such as fever (usually greater than 102 F), chills, nausea, vomiting, headache, muscle pain, and fatigue; these symptoms are frequently ignored or attributed to other causes. The rash, abdominal pain, joint pains, and diarrhea usually develop about two to 14 days (incubation period) after an infected tick bite. The rash (red spots) usually begins on the wrists and ankles and spreads to the palms and soles of the feet, but some individuals (about 10%-15%) do not develop it. Other symptoms that may occur are loss of appetite, hallucinations, photosensitivity (sensitivity to light), eye redness, and excessive thirst.
Unless the patient tells the doctor a tick bite has happened, the doctor may not realize the patient may have RMSF. Children who get infected tick bites may not communicate this important fact to their parents or doctor; likewise, many adults do not remember or even notice getting a tick bite. The classic symptoms of RMSF are a tick bite followed by fever and a rash. If the patient does not exhibit all three symptoms (tick bite, fever, and rash), the diagnosis frequently either is not correct or is delayed. A delay in diagnosis may allow time for severe symptoms and/or complications to develop. Severe symptoms of RMSF are thrombocytopenia (low blood platelets that can lead to internal bleeding), hyponatremia (low sodium), meningismus (a condition of neck stiffness, headache, and possible fever suggesting brain membrane irritation), confusion, blindness, or coma that can result in poor health or death.
Rocky Mountain Spotted Fever Causes
RMSF is caused by R. rickettsii, which are bacteria that are Gram stain negative, aerobic coccobacilli (round and rod shaped) that must live within eukaryotic cells (cells, such as human cells, that have a nucleus bound by a membrane). The organisms only proliferate if they are inside of a eukaryotic cell. In most cases of human infections, the endothelial cells that line blood vessels are the cells that harbor the bacteria. These cells can be disrupted by the organisms, thus producing vascular permeability (leaky blood vessels) that results in macules (flat areas of skin color change) and eventually a petechial rash (red or purple spots about 1 mm-2 mm in diameter usually caused by broken blood vessels). This vascular permeability can occur throughout the body and eventually cause death.
Although RMSF is caused by R. rickettsii, the bacteria need to be transmitted to humans by a tick vector (carrier) infected with R. rickettsii. RMSF will not occur in people bitten by uninfected ticks. The following ticks have been shown to be vectors for RMSF: the mountain wood tick (Dermacentor andersoni), the American dog tick (Dermacentor variabilis), and the brown dog tick (Rhipicephalus sanguineus), with the first two as the primary vectors. Other ticks can be responsible as vectors in various worldwide regions.
Rocky Mountain spotted fever (RMSF) is an illness caused by infection with the bacterium Rickettsia rickettsia, which is transmitted by a bite from infected ticks.
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Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.