Rocky Mountain Spotted Fever

Rocky Mountain spotted fever is an infection transmitted by the bite of a tick. At first its symptoms are mild, but without treatment the disease can become serious and cause organ damage and death.

What Is Rocky Mountain Spotted Fever?

Rocky Mountain spotted fever (RMSF) is the most serious of the rickettsial (rih-KET-see-ul) infections, diseases caused by bacteria from the Rickettsiaceae family. These bacteria typically spread to people through blood-sucking parasites ^* such as ticks and fleas. In Rocky Mountain spotted fever, the bacterium Rickettsia rickettsii lives and reproduces in the Ixodidae (ik-SAH-dih-day) family of hard-bodied ticks, such as the American dog tick and the Rocky Mountain wood tick, before it infects people. Once it does infect a person, it enters cells lining the blood vessels and can cause serious disease.

Several of the disease's first symptoms can be confused with those of other infections. As the condition grows worse, it often causes a widespread rash, which led people to call RMSF "black measles" when it was described in the late nineteenth century. If the infection is not treated, it can damage several organ systems and sometimes lead to death.

The Rocky Mountain wood tick, Dermacentor andersoni, is one of the species of hard-bodied ticks responsible for spreading the bacterium that causes Rocky Mountain spotted fever. Once infected, a tick can carry the bacterium for life.

©S.J. Krasemann/Peter Arnold Inc.

How Common Is It?

Despite its name, the infection is not limited to the Rocky Mountains. It is found throughout the United States, and most cases actually occur in the southeastern part of the country. The disease also has been found in southern Canada, Mexico, some countries in Central America, and parts of South America. According to the U.S. Centers for Disease Control and Prevention, between 250 and 1,200 cases are reported in the United States each year, with most in children under the age of 15. About 5 percent of Rocky Mountain spotted fever cases are fatal, usually because a person does not receive treatment quickly.

Is It Contagious?

RMSF is not contagious from person to person. It can spread only from a tick to a person, usually through the tick's bite when it feeds. Rarely, people can become infected when they come into contact with tick droppings or dead ticks that have been crushed. The bacterium lives in the tick and survives from one generation of the parasite to the next. Female ticks can pass it to their eggs, and male ticks can pass it to females when they mate.

What Are the Infection's Signs and Symptoms?

Symptoms of infection include severe headache, fever, confusion, chills, nausea (NAW-zee-uh), vomiting, loss of appetite, and muscle pain. Many infections have these symptoms, so they may not be immediately identified as RMSF. As the disease worsens, it may cause joint pain, abdominal ^* pain, extreme thirst, hallucinations ^* , diarrhea (dye-uh-REE-uh), and a rash. The rash usually appears 3 to 6 days after the start of symptoms. It typically starts as small, pink spots that crop up on the wrists, lower part of the arms, and ankles. The rash does not itch, and over time the spots become raised. In many patients, a red, spotted rash develops that looks like dots of blood under the skin, often on the palms of the hands and the soles of the feet. Even though this rash is one of the most distinctive symptoms, it is not seen in every patient. As many as 10 percent to 20 percent of patients do not have the typical rash.

How Do Doctors Diagnose Rocky Mountain Spotted Fever?

Doctors usually identify the infection based on symptoms seen during an examination, reports of the disease in the area, and knowledge of a recent tick bite. Fever, rash, and history of a tick bite are considered the classic features of RMSF. The doctor also may take a blood sample to look for antibodies ^* to the bacteria.

What Is the Treatment?

People with RMSF often need to be in the hospital, where they can receive supportive care. The disease is treated with antibiotics, which are given as soon as a doctor suspects that a patient might have RMSF. Waiting until laboratory tests confirm the diagnosis could put the patient at greater risk, because the infection can progress so quickly. Patients continue taking the medicine for at least 3 days after the fever goes away.

The rash associated with Rocky Mountain spotted fever usually starts as small pink spots, which, over time, become raised.

©Ken E Greer

What Medical Complications Can Occur?

Treatment typically takes 5 to 10 days, but it can last much longer. Without treatment or with delayed treatment, severe cases of illness can lead to death. In addition, the disease can cause problems with the central nervous system ^* , the kidneys, the digestive system ^* , and the respiratory tract ^* . This can lead to partial paralysis ^* , hearing loss, meningitis ^* , heart failure, brain damage, kidney failure, and shock ^* .

How Can Rocky Mountain Spotted Fever Be Prevented?

It is important to take precautions to limit the risk of tick bites: for example, by avoiding walks through brush and dense vegetation in areas with lots of ticks. When a person spends time outside, it is a good idea to wear long pants, long sleeves, and socks, with the pants tucked into the socks. Light-colored clothing makes ticks easier to see, and insect repellent can protect exposed skin. After being outside in tick-infested areas, it is wise to remove clothing and check the body, including the hair, thoroughly for the parasites. Doctors recommend that any ticks that are found be removed right away; the longer the tick stays attached, the greater the chance that the RMSF bacterium can enter the body.