Rocky Mountain Spotted Fever
Rocky Mountain spotted fever (spotted fever, tick fever, tick typhus) is a rickettsial disease that is transmitted by dog ticks and wood ticks and causes a rash, headache, and high fever.
Rocky Mountain spotted fever (RMSF) is caused by the bacterium Rickettsia rickettsii and is probably the most common rickettsial infection in the United States. Despite its name, this disease is found throughout most of the continental United States. It is most common in the Midwest and on the southern Atlantic seaboard. The disease occurs mainly from March to September, when adult ticks are active and people are likely to be in tick-infested areas. In the southern states, the disease may occur throughout the year. People who spend a lot of time in tick-infested areas--such as children younger than age 15--have an increased risk of infection.
Ticks acquire rickettsiae by feeding on infected mammals. Infected female ticks can also transmit rickettsiae to their offspring. Rickettsial disease is not transmitted directly from person to person.
Rickettsiae live and multiply in the cells lining blood vessels. Blood vessels in and under the skin and in the brain, lungs, heart, kidneys, liver, and spleen are commonly infected. Small blood vessels that develop the infection may become blocked by blood clots.
Symptoms
Typically, symptoms include a severe headache, chills, extreme exhaustion (prostration), and muscle pains. Symptoms begin suddenly 3 to 12 days after a tick bite. A high fever develops within several days and, in severe infections, persists for 1 to 2 weeks. A hacking, dry cough may also develop.
On about the fourth day of the fever, a rash appears on the wrists and ankles and rapidly extends to the palms, soles, forearms, neck, face, armpits, buttocks, and trunk. At first, the rash is flat and pink, but later darkens and becomes slightly raised. It does not itch. Warm water--for example, from a bath--makes the rash more evident. In about 4 days, small purplish areas (petechiae) develop because of bleeding in the skin. An ulcer may form where these areas merge.
If the blood vessels in the brain are affected, the person may have a headache, restlessness, insomnia, or delirium. Coma may develop. Nausea and vomiting and abdominal pain may also occur. Inflammation of the airways (pneumonitis) and pneumonia can develop. Also, heart damage and anemia may occur. Although uncommon, low blood pressure and death occur in severe cases.
Prevention and Treatment
There is no vaccine against RMSF, so avoiding tick bites is the best prevention. Tucking trousers into boots or socks and applying permethrin-containing insecticide to clothing limits tick access to skin. Tick repellents such as DEET (diethyltoluamide) may be applied to the skin. These repellents are effective but rarely cause toxic reactions, such as seizures, in small children. Conducting frequent searches for ticks is an important strategy for preventing infection, because the tick must be attached for 24 hours on average to transmit infection. Attached ticks should be removed carefully with tweezers; the head of the tick should be grasped as close to the skin as possible. Rickettsiae may be transmitted if an infected tick that is engorged with blood is crushed while being removed.
Because RMSF can cause serious illness or death, a doctor immediately prescribes antibiotics if he suspects RMSF based on a person's symptoms and potential for exposure to the disease--even if laboratory test results are not yet available. Tetracycline, doxycycline, and chloramphenicol are effective antibiotics for RMSF. They are given by mouth for mild disease and intravenously for more serious infections. Antibiotic therapy has significantly reduced the death rate from about 20% to 5%. Death is more likely when treatment is delayed. However, because most tick bites do not result in RMSF, a doctor usually does not prescribe antibiotics for a person who has simply had a tick bite. Instead, the doctor may ask the person to immediately report symptoms.
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