Rickettsial Infections

Rickettsial (rih-KET-see-ul) infections include those diseases caused by bacteria from the Rickettsiaceae family.

The diseases caused by rickettsial infections are alike in many ways. Rocky Mountain spotted fever, typhus (TIE-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.

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, compared to fewer than 100 typhus cases, and between 100 and 600 cases of ehrlichiosis.

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 infection-causing bacteria 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.

Medical professionals first recognized Rocky Mountain spotted fever in the Rocky Mountain states (such as Idaho, Montana, and Colorado), but after that they found it throughout the United States. A tick bite transmits the Rickettsia rickettsii bacte-rium. 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 can appear in several forms, including epidemic * typhus, murine typhus, and Brill's disease (also called 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.

Epidemic typhus is a much more severe disease, which is associated with a drop in blood pressure and stupor * or delirium * , and it can be fatal. Epidemic typhus spreads from person to person by body lice.

Brill's disease is a recurrence of epidemic typhus and, therefore, appears in people who have had epidemic typhus in the past. People who are vulnerable to Brill's disease are those whose immune system has been weakened by stress or by illness. It happens because the body's defenses are down, and this allows organisms left over from the earlier bout of illness to reactivate. Brill's disease causes mild symptoms and is not fatal.

Q fever results from 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 (di-ah-RE-a), chest and belly pain, and jaundice * can also accompany Q fever. People who work with animals, such as veterinarians, farmers, and slaughterhouse workers, are most at risk for the disease, which is transmitted when they breathe in the airborne bacteria that come from the animals’ bowel movements, milk, urine, or fluids from giving birth.

Infection with the species of Ehrlichia (air-LIH-kee-uh) bacteria—E. chaffeensis and E. phagocytophila—cause ehrlichiosis. 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.

Medical professionals diagnose rickettsial infections 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. In some cases, doctors may order a skin biopsy * of the rash to help in making the diagnosis. To avoid potentially serious complications, doctors often begin treatment even before they have test results to confirm their diagnoses.

Medical professionals treat all of these diseases 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, the patient may require hospitalization and treatment with intravenous * (IV) antibiotics and fluids.

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

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

The best way to prevent Q fever is to regularly test animals for infection and isolate any that are infected. Doctors recommend that people who work with animals wash hands and launder clothes carefully to lower their risk of infection.

See also Bacterial Infections • Rocky Mountain Spotted Fever • Tick-Borne Illnesses: Overview • Typhus • Zoonoses: Overview

* arthropods are members of a group of organisms that lack a spinal column and have a segmented body and jointed limbs. This group includes various insects, ticks, spiders, lice, and fleas.

* epidemic (eh-pih-DEH-mik) is an outbreak of disease, especially infectious disease, in which the number of cases suddenly becomes far greater than usual. Usually epidemics are outbreaks of diseases in specific regions, whereas widespread epidemics are called pandemics.

* stupor is a state of sluggishness or impaired consciousness.

* delirium (dih-LEER-e-um) is a condition in which a person is confused, is unable to think clearly, and has a reduced level of consciousness.

* jaundice (JON-dis) is a yellowing of the skin, and sometimes the whites of the eyes, caused by a buildup in the body of bilirubin, a chemical produced in and released by the liver. An increase in bilirubin may indicate disease of the liver or certain blood disorders.

* seizures (SEE-zhurs), also called convulsions, are sudden bursts of disorganized electrical activity that interrupt the normal functioning of the brain, often leading to uncontrolled movements in the body and sometimes a temporary change in consciousness.

* coma (KO-ma) is an unconscious state, like a very deep sleep. A person in a coma cannot be awakened, and cannot move, see, speak, or hear.

* 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.

* biopsy (BI-op-see) is a test in which a small sample of skin or other body tissue is removed and examined for signs of disease.

* intravenous (in-tra-VEE-nus), or IV, means within or through a vein. For example, medications, fluid, or other substances can be given through a needle or soft tube inserted through the skin's surface directly into a vein.

* pneumonia (nu-MO-nyah) is inflammation of the lungs.

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

* chronic (KRAH-nik) means lasting a long time or recurring frequently.

* endocarditis (en-do-kar-DYE-tis) is an inflammation of the valves and internal lining of the heart, known as the endocardium (en-doh-KAR-dee-um), usually caused by an infection.

* hepatitis (heh-puh-TIE-tis) is an inflammation of the liver. Hepatitis can be caused by viruses, bacteria, and a number of other noninfectious medical conditions.