Rickettsial Infections

Rickettsial (rih-KET-see-ul) infections are a collection of diseases caused by bacteria from the Rickettsiaceae family.

What Are They?

The diseases caused by rickettsial infections are alike in many ways. Rocky Mountain spotted fever, typhus (TY-fis), ehrlichiosis (air-lik-e-O-sis), and Q fever all have similar symptoms, including headache, high fever, and sometimes a rash. These infections also respond to the same type of treatment, and many of them spread in the same way: through the bites of blood-sucking arthropods ^* , such as lice, fleas, and ticks.

How Common Are Rickettsial Infections?

These infections do not occur frequently in the United States (although typhus is relatively common in other parts of the world, especially the tropics). Rocky Mountain spotted fever is the most common rickettsial infection in the United States: up to 1,200 cases are reported yearly. Fewer than 100 typhus cases are reported annually, and a total of about 1,200 cases of ehrlichiosis have been reported during an 11-year period.

Are They Contagious?

Rickettsial infections do not spread directly from person to person. Instead, most require blood-sucking arthropods, such as lice, ticks, and fleas, to carry the organisms between animals and people or from one person to another. When a flea, for example, bites an infected animal or person, it can ingest the infectious bacteria. If the flea then bites someone else, it can spread the disease to that person. In the case of Rocky Mountain spotted fever, however, the bacterium lives and reproduces within ticks. Once a tick acquires the bacterium (from its mother when it is still an egg or through mating or feeding on an infected animal) it can infect people for the rest of its life. Q fever mainly spreads from livestock animals to people. The bacteria can pass into the animals' bowel movements, milk, urine, or fluids that accompany giving birth. People become infected by breathing in the bacteria in airborne bits of dust contaminated with one of those substances.

Specific Infections

Rocky Mountain spotted fever

Rocky Mountain spotted fever first was recognized in the Rocky Mountain states (such as Idaho, Montana, and Colorado) but since then it has been found throughout the United States. It is caused by the Rickettsia rickettsii bacterium, which is transmitted by tick bites. The disease is most common in children, usually in tick-infested areas, where outdoor work and play create the most risk.

Symptoms of infection include a severe headache, muscle pain, chills, fever, confusion, and a rash that appears first on the wrists and ankles before spreading. About 5 percent of Rocky Mountain spotted fever cases are fatal, usually because a person does not receive treatment quickly.

Typhus

Typhus can appear in several forms, including epidemic ^* typhus, murine typhus, and Brill-Zinsser disease. The bacteria that cause typhus, Rickettsia prowazekii and Rickettsia typhi, spread to people through the bites of fleas or lice. People who are infected can become very sick and often have a fever that may climb as high as 105 to 107 degrees Fahrenheit. Murine typhus is the variety seen most often in the United States, usually in the southern and southeastern states. People who come into contact with fleas that feed on rats, opossums, and outdoor cats are at the greatest risk for the disease. Once someone becomes infected, that person may experience a headache, a rash, nausea (NAW-zee-uh), joint pain, belly pain, vomiting, and a dry cough. The disease is rarely fatal. Most people recover with few complications.

Murine typhus is a milder form of epidemic typhus, which is associated with a drop in blood pressure and stupor ^* or delirium ^* , and it can be fatal. Epidemic typhus is spread from person to person by body lice. Brill-Zinsser disease is a recurrence of epidemic typhus that appears in someone who was infected before that person's immune system was weakened by stress or illness. When the body's defenses are down, organisms left over from the earlier bout of illness may reactivate. The disease causes mild symptoms and is not fatal.

Q fever

Q fever is caused by the bacterium Coxiella burnetii, which lives primarily in farm animals, such as sheep, goats, and cattle. People who contract the infection may have no symptoms at all or may experience symptoms similar to those of the flu, such as fever, muscle and joint aches, severe headache, and dry cough. Nausea, vomiting, diarrhea (dyeuh-REE-uh), chest and belly pain, and jaundice ^* also can accompany Q fever. People who work with animals, such as veterinarians, farmers, and slaughterhouse workers, are most at risk for the disease, which is contracted by breathing in the bacteria from the animals' bowel movements, milk, urine, or fluids from giving birth.

Ehrlichiosis

Ehrlichiosis is caused by infection with the species of Ehrlichia (air-LIH-kee-uh) bacteria E. chaffeensis and E. phagocytophila. Tick bites spread the bacteria to people, where the infection produces symptoms similar to those of Rocky Mountain spotted fever. Severe cases can damage many organ systems and lead to seizures ^* , coma and death.

How Do Doctors Make the Diagnosis?

Rickettsial infections are diagnosed by finding antibodies ^* to the organism in the blood. These antibodies usually are not present early in the illness, so a doctor relies on the patient's history of symptoms, a physical examination, and information about where the person lives or became sick to make the diagnosis. To avoid potentially serious complications, it is important not to delay treatment of rickettsial infections while waiting for test results. In some cases, a skin biopsy ^* of the rash can aid in making the diagnosis.

What Is the Treatment for Rickettsial Infections?

All of these diseases are treated with antibiotics. Patients begin taking the medication as soon as possible, because a delay in treatment may increase the risk of complications. In more serious cases, often those in which the diagnosis has been delayed, it may be necessary to hospitalize patients and treat them with intravenous ^* (IV) antibiotics and fluids.

How Long Does a Rickettsial Infection Last?

The infections typically last from 1 week to several weeks. If they go untreated or if treatment does not begin soon after infection, the disease can linger for months.

What Are the Complications?

Untreated and severe cases of any of these diseases can be fatal. In addition, each rickettsial illness has its unique complications:

• Rocky Mountain spotted fever can cause paralysis ^* , hearing loss, and nerve damage.
• Typhus can lead to pneumonia ^* , kidney ^* problems, and problems with the central nervous system ^* .
• Chronic ^* Q fever in the elderly can cause endocarditis ^* and hepatitis ^* .
• Ehrlichiosis can damage various organs, including the lungs, kidneys, and brain.

How Are Rickettsial Infections Prevented?

People can take steps to protect themselves from infection by avoiding flea, tick, and louse bites. It is recommended that anyone who works or plays outdoors be particularly careful. Avoiding areas that are infested with lice, ticks, and fleas or using insecticides and repellents in those areas can help. Wearing long pants and long-sleeved shirts, especially in spots with thick bushes or tall grass, also can guard against bites. After spending time outside in areas where ticks are found, people should examine their bodies carefully, including the hair, to make sure that there are no ticks. It is wise to check pets regularly for ticks, too, because animals can carry parasites into the house.

Q fever is best prevented by regularly testing animals for infection and isolating those that are infected. Doctors recommend that people who work with animals wash hands and launder clothes carefully to lower their risk of infection.