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.

KEYWORDS

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Ixodidae ticks

Rickettsia rickettsii

Rickettsial infections

Zoonoses

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.

* tick is a small blood-sucking creature that may transmit disease-causing germs from animals to humans through its bite.

* parasites (PAIR-uh-sites) are organisms such as protozoa (one-celled animals), worms, or insects that must live on or inside a human or other organism to survive.

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.
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.

* abdominal (ab-DAH-mih-nul) refers to the area of the body below the ribs and above the hips that contains the stomach, intestines, and other organs.

* hallucinations (ha-loo-sin-AY-shuns) occur when a person sees or hears things that are not really there. Hallucinations can result from nervous system abnormal ties, mental disorders, or the us of certain drugs.

* antibodies (AN-tih-bah-deez) are protein molecules produced by the body's immune system to help fight specific infections caused by microorganisms, such as bacteria and viruses.

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
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 * .

Dr. Ricketts

Even if you have heard about Rocky Mountain spotted fever, you may not know the name Howard T. Ricketts. Dr. Ricketts discovered the bacterium behind the disease and figured out that it spreads to people through tick bites. In recognition of that work, Rickettsia rickettsii the RMSF bacterium, received its double Ricketts name. Dr. Ricketts also did research on typhus (TY-fis), another rickettsial infection. He died of typhus in 1910.

* central nervous (SEN-trul NER-vus) system is the part of the nervous system that includes the brain and spinal cord.

* digestive system is the system that processes food. It includes the mouth, esophagus, stomach, intestines, colon, and rectum and other organs involved in digestion, including the liver and pancreas.

* respiratory tract includes the nose, mouth, throat, and lungs. It is the pathway through which air and gases are transported down into the lungs and back out of the body.

* paralysis (pah-RAH-luh-sis) is the loss or impairment of the ability to move some part of the body.

* meningitis (meh-nin-JY-tis) is an inflammation of the meninges, the membranes that surround the brain, and the spinal cord. Meningitis is most often caused by infection with a virus or a bacterium.

* shock is a serious condition in which blood pressure is very low and not enough blood flows to the body's organs and tissues. Untreated, shock may result in death.

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.

Resources

Organization

U.S. Centers for Disease Control and Prevention (CDC), 1600 Clifton Road, Atlanta, GA 30333. The CDC provides a fact sheet and other information on rickettsial infections.
Telephone 800-311-3435
http://www.cdc.gov

Website

KidsHealth.org . KidsHealth is a website created by the medical experts of the Nemours Foundation and is devoted to issues of children's health. It contains articles on a variety of health topics, including Rocky Mountain spotted fever.
http://www.KidsHealth.org

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