Rocky Mountain Spotted Fever

Rocky Mountain spotted fever (RMSF) facts

• Rocky Mountain spotted fever is caused by the bacterium Rickettsia rickettsii.
• The bacterium is spread to humans through the bite of infected ticks, and so the disease is most common in months where ticks are active, such as summer.
• Despite the name, the disease is not limited to the Rocky Mountains but rather occurs throughout most of the U.S.
• Symptoms of headache, fever, and fatigue begin about a week after exposure. A few days later, a rash develops. The rash may be so mild that it is hard to see or so dramatic that it progresses to gangrene. Other possible symptoms include confusion, abdominal pain, and vomiting.
• Most cases require hospitalization, and severe cases require intensive care.
• The disease is diagnosed by finding high titers of antibodies in the blood or by seeing the organism under a microscope in specially stained skin biopsies.
• The treatment of choice is the antibiotic doxycycline (Vibramycin, Oracea, Adoxa, Atridox). Prompt treatment improves survival and reduces complications.
• Most people with RMSF recover completely over a few weeks. In severe cases, patients may have brain damage or other neurological problems that persist after treatment.
• The risk of RMSF can be reduced by reducing exposure to ticks. This includes avoiding areas that have large concentrations of ticks, using insect repellents and wearing protective clothing.
• Because the risk of infection increases with the duration of tick attachment, people should check themselves for ticks when they return from an outing.

What is Rocky Mountain spotted fever?

Rocky Mountain spotted fever is a bacterial infection that is transmitted to humans through the bite of a tick. Statistics show that rates of disease have been rising steadily over the past decade. Although most people recover completely, fatalities occur in approximately 0.5%-5% of cases.

Where do most cases of RMSF occur in the U.S.?

Cases of RMSF have been reported from most areas of the country, and the disease is not restricted to the Rocky Mountain region. In fact, Arkansas, Missouri, North Carolina, Oklahoma, and Tennessee account for over 60% of reported cases. In 2008, there were approximately 2,500 cases reported in the U.S., which is more than twice as many cases as were reported annually in the 1990s.

Reported incidence of RMSF per million people in 2008; NN=not reported. SOURCE: CDC.

What is the history of Rocky Mountain spotted fever?

RMSF was first described in the late 1800s in the Snake River Valley of Idaho. Initially, cases were thought to be confined to the Rocky Mountain area, but by the early 20th century, it was obvious that the disease occurred in areas throughout the country. Dr. Howard Ricketts identified the causative organism in the blood of infected people and showed that ticks could transmit the organism. Many other scientists worked to identify the characteristics of the disease and the tick vector, but it was not until the middle of the 20th century that an effective treatment was discovered. Many of the early researchers died of tick-borne infections while studying the disease.

What causes Rocky Mountain spotted fever?

RMSF is caused by a small bacterium known as Rickettsia rickettsii. R. rickettsii lives inside the cells that line the blood vessels of infected animals and humans.
The tick is the primary home or reservoir for R. rickettsii. Because ticks can also spread the organism to humans and other animals, they are sometimes referred to as vectors for transmission of RMSF. Several different types of ticks can carry R. rickettsii. For example, the American dog tick (Dermacentor variabilis) is the most common vector in the eastern, central, and Pacific U.S. In the West, the Rocky Mountain wood tick (Dermacentor andersoni) is the primary vector for RMSF. Ticks can pass the organism to their offspring, creating a new generation of infected ticks. Ticks can also be infected by feeding on an infected person or animal. Even in the woodlands and fields of high-risk areas, only a small proportion of ticks will carry R. rickettsii.

Picture of a Rocky Mountain wood tick. SOURCE: CDC/Dr. Christopher Paddock.

Picture of American dog ticks.

What are risk factors for Rocky Mountain spotted fever?

Cases of RMSF occur when the appropriate tick vector comes in contact with human populations. Risk factors include traveling to an area with a high rate of RMSF, especially in seasons when ticks are plentiful, such as summer. People at highest risk are those who frequent forested areas or fields, such as those who are hiking or camping. Even urban outdoor areas pose a risk, however. Dog ownership is a risk factor in areas where the American dog tick exists. Dogs acquire ticks while roaming outside, and these ticks can be transferred to humans during petting or other contact.
The risk of RMSF is thought to increase with the duration of tick attachment. A feeding tick can remain attached to a human for up to two weeks. Crushing an attached tick improperly may cause secretions from the tick to be injected into the skin and increase the risk of infection.
Severe disease is more common in the elderly, alcoholics, and in African Americans. The latter is at least partly due to delays in diagnosis of the typical rash in dark-skinned people. In addition, blacks are more likely to have a genetic enzyme deficiency (G6PD) that can make the disease more severe.

What are symptoms and signs of Rocky Mountain spotted fever in children and adults?

Symptoms appear within about a week of exposure to the bacteria (range two to 14 days). Initially, people feel like they have influenza (flu) with headache, high temperature, body aches, and fatigue. Other possible symptoms include abdominal pain, vomiting, and lack of appetite. Symptoms in children may be slightly different than in adults. Children may complain less of headache and more of abdominal pain, which may be severe. The eyes may be red (conjunctivitis).
A rash appears within three to five days, often starting around the wrists or ankles and then spreading to the trunk, palms, and soles. The rash starts as discrete, small red areas and resembles the rashes (exanthems) of many other viral illnesses. Over a few days, these areas may become bright red or purple and are known as petechiae, a sign of more severe disease. The petechiae may merge as the rash advances to create a diffuse redness.
In some cases, the rash may be so mild that it is missed on examination. People with dark skin often have delayed diagnosis because the rash is harder to detect. In severe cases, the skin may turn black and necrotic (meaning there is death of tissue), resembling gangrene.
Headache is often very severe and may be the presenting complaint, especially in adults. Other neurological signs that might appear include a stiff neck, difficulty hearing, confusion, and weakness or paralysis of some muscles. Severe cases may reduce the ability of the blood to clot, which causes the patient to be at risk for internal bleeding.
None of the above symptoms is specific for RMSF. Other tick-borne illnesses may cause similar symptoms, including other members of the spotted fever rickettsiosis group. Ticks may also spread other diseases such as Lyme disease.

Rocky Mountain spotted fever rash pictures. SOURCE: CDC.

How is Rocky Mountain spotted fever diagnosed?

Physicians should consider RMSF in a patient who has fever, headache, and other compatible symptoms, especially if the person has recently visited an area where the disease is known to occur. Because the disease is caused by ticks, it is seasonal and should be considered in months when ticks are active. A history of tick exposure is helpful, but it is important to remember that most ticks do not carry R. rickettsii and that many tick bites go unnoticed. The rash may appear late in the course of disease or be very mild, so it is important to think of the disease even if the rash is not present. If the facts of the case make the diagnosis appear to be likely, treatment should not be delayed to wait for the rash or results of tests.
RMSF is diagnosed through several methods. Using immunohistochemistry, a small piece of skin can be mixed with a special stain that allows the organism to show up under the microscope. Because the presence of the organism in skin may be patchy, a negative biopsy does not rule out the disease.
Blood can be tested for antibodies to the organism using techniques known as immunofluorescence (IFA) or enzyme immunoassays (ELISA or EIA). If a high concentration of antibody is found, it can be presumed that disease is present. It may take a week for antibodies to appear, so a negative titer does not completely rule out the disease. Blood can also be tested for antibodies at the onset of illness and again several weeks later to see if there is a substantial change in the titer. Other tests, such as the polymerase chain reaction (PCR) to detect the genetic material of the bacteria are available in research laboratories or from the U.S. Centers for Disease Control and Prevention (CDC) although they have not been standardized for general use.
R. rickettsii is difficult to culture and requires living host cells to grow. It is also dangerous to grow, because there have been cases of laboratory technicians getting sick while performing the culture. Only laboratories that are certified to handle this level of biohazard should attempt to culture the organism.
Most other laboratory findings are nonspecific, meaning that they cannot be used alone to make the diagnosis. White blood cell counts may be normal or increased slightly, or anemia may be present. Platelet counts may be decreased, especially in severe cases. Serum sodium levels are low in about half of patients, and liver enzyme tests in the blood may be elevated. If kidney failure occurs, the serum creatinine will be increased. If neurological symptoms occur, the spinal fluid may show increased numbers of white cells or an increased concentration of proteins.

What is the treatment for Rocky Mountain spotted fever in children and adults?

RMSF is treated with antibiotics, usually from the tetracycline class. Doxycycline is the most commonly recommended antibiotic for this purpose and is usually taken orally twice a day for seven days. An intravenous form is available for patients who are unable to tolerate the oral form.
Special comment should be made for one population in need of treatment: children. Doxycycline is not used routinely in young children (< 8 years of age) because it might cause staining of teeth, but this almost never occurs with a limited one-week course. Since the risk is minor compared to the potential severity of RMSF, both the CDC and the American Academy of Pediatrics recommend doxycycline for all children with RMSF. Similarly, doxycycline is usually not given to pregnant women because of the potential effect of the drug on fetal bones and teeth. However, the risk must be weighed against the benefit of treatment on an individual basis. If a person cannot take doxycycline, there are other possible choices, including an older agent called chloramphenicol. Chloramphenicol also has toxicities. Use of alternative agents or treatment during pregnancy warrants consultation with a specialist experienced in the area.

What are complications of Rocky Mountain spotted fever?

Complications of RMSF include kidney failure, neurological problems, bleeding, gangrene, and death. Most patients with a diagnosis of RMSF are hospitalized and severe cases require intensive care. Death occurs in approximately 0.5%-5% of treated cases and up to 20% of untreated cases.

What is the prognosis of Rocky Mountain spotted fever in children and adults?

Most people with RMSF recover completely over a few weeks. People with severe neurological symptoms may have residual difficulty with balance during walking (ataxia), blindness, and brain damage.

How can people safely remove a tick?

A tick can be removed by grasping it with tweezers very close to the skin and pulling gently. Avoid squeezing/crushing the main tick body to limit the opportunity to eject infected secretions. Do not use nail polish, petroleum jelly, or heat to try to make the tick drop off.

Can Rocky Mountain spotted fever be prevented?

The risk of RMSF can be reduced by avoiding areas where ticks are common. If a person does go into such an area, protective clothing including socks, long pants, and long sleeves will reduce that area of skin available for a tick. Insect repellents containing DEET reduce the risk of tick bites. The risk of disease increases with the duration of tick attachment, so the body should be checked carefully for ticks after returning from an outing. Because most ticks are not infected, doxycycline is not recommended after a tick bite in a person who has no symptoms.

Where can people find more information on Rocky Mountain spotted fever?

The CDC is an excellent source of information on RMSF, available online at http://www.cdc.gov/rmsf.

REFERENCE:

United States. Centers for Disease Control and Prevention. "Diagnosis and Management of Tickborne Rickettsial Diseases: Rocky Mountain Spotted Fever, Ehrlichioses, and Anaplasmosis -- United States." Morbidity and Mortality Weekly Report 55(RR04) (2006): 1-27.

Medical Author:

Mary D. Nettleman, MD, MS, MACP

Medical Editor:

Melissa Conrad Stöppler, MD

Source:Medicinenet.com.