Rocky Mountain Spotted Fever

Rocky Mountain spotted fever (RMSF) is a disease caused by the bacterium Rickettsia rickettsii which is spread to humans by ticks. Symptoms can include the sudden onset of fever, headache, and muscle pain followed by the development of a rash. The disease can be difficult to diagnose in the early stages, and without prompt treatment, it can be fatal.



Other Names

 * RMSF
 * Black measles

Signs and Symptoms
Rocky Mountain spotted fever can be difficult to diagnose in its early stages, even by experienced health care workers who are familiar with the disease. Symptoms typically occur 5 to 10 days after a tick bite.

The first symptoms of RMSF may include the following:


 * Moderate to high fever, which can persist for two to three weeks if the infection is untreated.
 * Nausea
 * Vomiting
 * Severe headache
 * Deep muscle pain
 * Significant tiredness
 * Chills
 * Lack of appetite

A rash usually develops two to five days after the fever begins. The red-spotted rash often starts as small, flat, pink, non-itchy spots on the wrists, forearms, and ankles. These spots turn pale when pressure is applied. They eventually become raised on the skin. After six or more days of the illness, the rash can develop into dark red spots which represents tiny areas of bleeding under the skin (called a petechial rash). The rash may involve the palms of the hands and soles of the feet at any stage, although this is more commonly seen in the later stages. In a few people, R. rickettsii can severely damage very small blood vessels in the skin. This can lead to the death of skin tissue and the formation of black spots or gangrene. This rare form of the illness led to the name black measles.

Up to 10% to 15% of people with RMSF never develop a rash, a condition often referred to as "Rocky Mountain spotless fever".

Some people develop additional symptoms later in the disease, including abdominal pain, joint pain, and diarrhea.

Causes
Rocky Mountain spotted fever is caused by the bacterium known as Rickettsia rickettsii. R. rickettsii is a small bacterium that grows inside the cells of the organism it is infecting. In the human body, rickettsiae live and multiply mainly in cells that line small- to medium-sized blood vessels. Such infected cells become damaged, allowing blood to leak through tiny holes in the blood vessel wall to surrounding tissue. The result is the classic petechial rash seen in RMSF.

The genus Rickettsia is included in the bacterial tribe Rickettsieae, family Rickettsiaceae, and order Rickettsiales. This genus includes many other species of bacteria associated with human disease, including those in the spotted fever group and in the typhus group. More than 20 species are currently recognized in genus Rickettsia but not all are known to cause disease in humans. Other genotypes are also known but they have not been classified yet as valid species and new agents are being discovered in many areas of the world.

Diagnosis
A health care provider can diagnose Rocky Mountain spotted fever by evaluating the symptoms and doing laboratory tests. RMSF can cause an abnormal white blood cell count, a low platelet count, decrease in sodium levels in the body, or an increase in liver function tests.

Blood tests used to confirm a case of RMSF include the indirect immunofluorescence assay (IFA), enzyme-linked immunosorbent assay (ELISA), latex agglutination, and dot immunoassays. Most reference and public health laboratories use the IFA test. These tests are not always useful in the immediate diagnosis of RMSF as they may take several days to weeks to become positive.

In cases where the diagnosis is unclear, a small skin biopsy can be taken and tested for evidence of rickettsiae infection using a polymerase chain reaction (PCR) test (which looks for microbial DNA), or an immunostaining method.

Treatment
A health care provider will treat Rocky Mountain spotted fever with an antibiotic, usually doxycycline. Treatment should be started as soon as possible after a diagnosis of RMSF is entertained. Treatment should not be delayed while waiting for the results of confirmatory laboratory tests. If appropriate antibiotics are started within the first four to five days of illness, fever generally resolves within 24 to 72 hours. In more severe cases, fever may take longer to disappear.

Anyone started on treatment needs to continue to take the medicine for at least three days after the fever goes away and after the symptoms end.

Doxycycline and other tetracyclines are not recommended for use in women who are pregnant because of risks to the unborn child. An alternative antibiotic that can be used is chloramphenicol, although this drug is associated with a number of side effects.

Prevention
To help prevent RMSF, avoid walking in areas of tall grass and brush where there may be ticks. If it is necessary to go into these areas, the following measures can help reduce the risk:


 * Wearing light-colored clothing.
 * Tucking pant legs into socks so ticks cannot get up inside the pants legs.
 * Wearing a long-sleeved shirt and tucking it inside the pants.
 * Spraying insecticide containing permethrin on boots and clothing. The effects will last several days.
 * Applying insect repellent containing DEET to the skin. Because DEET lasts only a few hours, it may need to be reapplied.
 * Looking for ticks on the body, including in the hair, after returning from hiking or walking.
 * Checking children and pets for ticks.

Generally, a tick needs to be attached to the body for at least 24 hours before it can infect a person. The tick needs to be removed with fine-tipped tweezers. The Centers for Disease Control and Prevention (CDC) recommends the following procedure for removing ticks:
 * 1) Use fine-tipped tweezers or notched tick extractor, and protect the fingers with a tissue, paper towel, or latex gloves. Persons should avoid removing ticks with their bare hands.
 * 2) Grasp the tick as close to the skin surface as possible and pull upward with steady, even pressure. Do not twist or jerk the tick; this may cause the mouthparts to break off and remain in the skin. (If this happens, remove mouthparts with tweezers. Consult a health care provider if illness occurs.)
 * 3) After removing the tick, thoroughly disinfect the bite site and wash hands with soap and water.
 * 4) Do not squeeze, crush, or puncture the body of the tick because its fluids may contain infectious organisms. Skin accidentally exposed to tick fluids can be disinfected with iodine scrub, rubbing alcohol, or water containing detergents.
 * 5) Save the tick for identification in case illness occurs. This may help the doctor make an accurate diagnosis. Place the tick in a sealable plastic bag and put it in a freezer. Write the date of the bite on a piece of paper with a pencil and place it in the bag.

How is Spread
RMSF disease is spread from the bite of an infected tick. In the United States, the American dog tick (Dermacentor variabilis) and the Rocky Mountain wood tick (Dermacentor andersoni) are the main vectors (carriers) of RMSF bacteria. The wood tick is found mainly in the Rocky Mountain States, including Montana, Idaho, Colorado, Wyoming, Utah, and Nevada.

The dog tick is found from the Great Plains to the East Coast, in Alaska and Hawaii, and in parts of California. The dog tick is not found in the interior northwest.

Other tick species, such as Amblyomma americanum, can occasionally transmit RMSF.

Complications
RMSF can be a very severe illness that requires hospitalization. The bacteria infect cells that line blood vessels throughout the body. This infection can cause problems in the respiratory system, central nervous system, gastrointestinal system, or kidneys.

Some people infected with RMSF develop long-term health problems including the following:


 * Partial paralysis of the legs.
 * Gangrene requiring amputation of fingers, toes, arms, or legs.
 * Hearing loss.
 * Loss of bowel or bladder control.
 * Difficulty moving.
 * Language disorders.

These problems are most frequent in those recovering from severe, life-threatening disease, often following lengthy hospitalizations.

Research
Because of the work started by Dr. Ricketts in the early 1900s, the National Institute of Allergy and Infectious Disesases Rocky Mountain Laboratories (RML) remains a thriving center for infectious disease research on tickborne diseases, such as Lyme disease and relapsing fever. RML also maintains active studies on Rickettsial diseases including RMSF.

History
RMSF was discovered in 1896 and was originally called black measles because of the look of its rash in the late stages of the illness, when the skin turns black. It was a dreaded, often fatal disease, affecting hundreds of people in Idaho. By the early 1900s, the disease could be found in western states as far north as Washington and Montana and as far south as California, Arizona, and New Mexico.

In response to this health problem, the U.S. Public Health Service sent University of Chicago pathologist Dr. Howard T. Ricketts to the Bitterroot Valley of Montana, one of the disease hotspots. In 1906 Dr. Ricketts demonstrated that the disease was transmitted by the bite of the Rocky Mountain wood tick. The work of Dr. Ricketts laid the foundation for what later became the Rocky Mountain Laboratories (RML) in Hamilton, Montana. Today, hundreds of scientists continue to study tickborne as well as other diseases at RML, which is now part of the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health in Bethesda, Maryland.

Epidemiology
RMSF is found throughout the United States from April through September. More than half of all cases occur in the mid-Atlantic to southern region of the United States (Delaware, Maryland, Washington, D.C., Virginia, West Virginia, North Carolina, South Carolina, Georgia, Oklahoma, and Florida). North Carolina and Oklahoma report the greatest number of people with RMSF. Although the disease was first discovered in the Rocky Mountains, that area has relatively few cases today. The disease also has been found in Canada and in Central and South America.

Prevalence
Though U.S. health care providers typically report about 250 to 1,200 cases of RMSF each year to the Centers for Disease Control and Prevention (CDC), a record 1,514 cases were reported in 2004.