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.

*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.

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.

*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 worldwide epidemics are called pandemics.

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.

*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.

Historical Importance of Typhus

Epidemic typhus has a long history of causing death in times of war. Poor sanitation and the presence of lice and rats in crowded living quarters have contributed to high rates of illness and death among soldiers: During the Napoleonic War, the French defeat in Russia in 1812 was attributed to typhus. Conditions were no better by World War I: Thousands of soldiers had fallen victim to typhus by the war’s end. It was not until the time of World War II that the disease could be controlled with vaccinations*, antibiotics, and more sanitary conditions. Typhus also has been referred to as “jail fever,” because epidemics would periodically sweep through prisons, where filthy conditions made a home for rats and lice.

*vaccinations: (vak-sih-NAY-shunz), also called immunizations, are the giving of doses of vaccines, which are preparations of killed or weakened germs, or a part of a germ or product it produces, to prevent or lessen the severity of a disease.

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 (dye-uh-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.

*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.

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.

*seizures: (SEE-zhurs) 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 in which a person cannot be awakened and cannot move, see, speak, or hear.

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.

*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.

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.

*intravenous: (in-tra-VEE-nus) 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.

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.

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

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

*kidney: is one of the pair of organs that filter blood and remove waste products and excess water from the body in the form of urine.

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

*chronic: (KRAH-nik) means continuing for a long period of time.

*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.

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.

See also

Ehrlichiosis

Endocarditis, Infectious

Hepatitis, Infectious

Rocky Mountain Spotted Fever

Tick-borne Infections

Zoonoses

Resources

Organization

U.S. Centers for Disease Control and Prevention (CDC), 1600 Clifton Road, Atlanta, GA 30333. Through the website of the National Center for Infectious Diseases, the CDC provides fact sheets and other information on rickettsial infections.

Telephone 800-311-3435 http://www.cdc.gov/ncidod/

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

Complete Human Diseases and Conditions

Rickettsial Diseases

views updated May 17 2018

RICKETTSIAL DISEASES

The term "Rickettsial diseases" is loosely applied to a variety of infectious diseases caused by gramnegative fastidious bacteria belonging to the genera Rickettsia, Orientia, Ehrlichia, and Coxiella. This grouping is justified by historical aspects of the discovery of each microorganism, by similarities in their microbiological and ecological characteristics, and by their association with arthropod vectors (lice, fleas, ticks, and mites). Rickettsial diseases described in this section include both classical

Table 1

Rickettsial Diseases of Humans
Disease¹	Organism	Invertebrate vector	Reservoir/Mammalian host	Typical mode of transmission to humans	Natural cycle	Geographic distribution
¹ Newly emerging diseases are indicated with a star (*)
² More details on epidemic typhus and R. prowazekii-associated infections can be found in the section: "Typhus."
³ SF – Spotted fever.
SOURCE : Courtesy of author.
Typhus group:
Epidemic typhus	R. prowazekii²	Human body louse	Human	Infected lice and their feces	Human-louse	Worldwide
Endemic (Murine) typhus	R. typhi	Flea, louse	Rodents	Infected flea feces	Rat-flea cycle	Worldwide
*Murine-typhus like infection	R. Felis (ELB agent)	Cat flea	Opossum, rats	Unknown	Transovarian in cat fleas and opossum-flea cycle	Worldwide
Spotted fever group:
Rickettsialpox	R. akari	Mouse mite	Mite/mice	Mouse mite bite	Transovarian in mites and mite-mouse cycle	Worldwide
Rocky Mountain spotted fever	R. rickettsii	Dog, wood tick	Tick, rodents, lagomorphs, canines	Tick bite	Transovarian in ticks and tick-rodent cycle	Western Hemisphere
Boutonneuse fever, Mediterranean SF³	R. conorii	Ixodid tick	Ticks, rodents, dogs	Tick-infested terrain, houses, dogs, tick bite	Transovarian in ticks	Africa, Southern Europe to India
*Astrakhan SF	Unnamed rickettsia	Ixodid tick	Dogs, hedgehog, ticks	Tick bite, aerosol	Unknown	Europe
North Asian tick typhus	R. sibirica	Ixodid tick	Rodents, canines	Tick bites	Transovarian in ticks and tick-rodent cycle	Europe, Asia
*African tick bite fever	R. africae	Ixodid tick	Ruminants	Tick bites	Transovarian in ticks	Sub-Saharan Africa
Queensland tick typhus	R. australis	Ixodid tick	Rodents, marsupials	Tick bite	Circulation in tick population	Australia
*Flinders Island SF	R. honei	Ixodid tick	Rodents, dogs	Tick bite	Unknown	Australia
*Oriental SF	R. japonica	Ixodid tick	Rodents	Tick bite	Unknown	Japan
Israeli tick typhus	R. sharonii	Ixodid tick	Dogs, rodents, hedgehog	Tick bite	Unknown	Israel
Scrub typhus group:
Scrub typhus (tsutsugamushi fever)	Orientia tsutsugamushi	Trombilicud mite	Rodents, marsupials	Chigger bite	Transovarian in mites	Southern Asia, Australia
Ehrlichioses:
*Human monocytic ehrlichiosis	Ehrlichia chaffeensis	Ixodid tick	Deer?	Tick bite	Tick-white deer	USA, Europe /Worldwide
*Human granulocytic ehrlichiosis	HGE agent	Ixodid tick	Horse, deer, cattle	Unknown	Tick-horse, deer, cattle	Northern USA, Europe
*Unknown disease	E. ewingii	Ixodid tick?	Dogs?	Unknown	Tick-dog?	USA
Sennetsu ehrlichiosis	E. sennetsu	Fluke?	Raw fish?	Unknown	Unknown	Japan, Malaysia

and newly emerging rickettsioses and ehrlichioses (see Table 1).

RICKETTSIOSES

The classical rickettsioses have been divided traditionally into several groups: louse- and flea-borne typhus group rickettsial diseases; tick- and mite-borne spotted fever group (SFG) rickettsial diseases, and chigger-borne scrub typhus. Epidemic typhus, murine typhus, spotted fevers, and scrub typhus share one dominant feature: widespread microvascular injury, which develops as a result of the invasion of, and multiplication of, rickettsiae in the cytoplasm of endothelial cells. Rickettsioses typically begin with an acute onset of symptoms one to two weeks after exposure to rickettsiae. Common symptoms include fever, severe headache, malaise, and myalgia. A rash often appears a few days after the onset of fever, the appearance of

Figure 1

which varies depending upon the type of disease. In scrub typhus, tick typhus, and rickettsialpox a specific skin lesion develops at the site of the infecting arthropod bite (see Figure 1).

Rocky Mountain spotted fever (RMSF), epidemic typhus, and scrub typhus are frequently life-threatening illnesses when left untreated. Murine typhus and the other spotted fever infections are typically milder, but they may have fatal outcomes in weakened patients.

Epidemic and recrudescent typhus, caused by R. prowazekii, are fatal to their infective louse hosts. Other forms, however, do not kill their arthropod hosts, increasing the possibilities of transmission. Pathogenic species of Rickettsia are also transmitted through their mammalian hosts. Humans get infected when they enter areas infested with infected arthropods. RMSF, endemic typhus, rickettsialpox, sylvatic epidemic typhus, and cat-flea transmitted R. felis infection are indigenous to the United States. Epidemic typhus

and endemic typhus occur worldwide. Mediterranean spotted fever, African tick bite fever, North Asian tick typhus, Flinders Island spotted fever, Oriental spotted fever, Queensland tick typhus and scrub typhus infections all have a specific geographical distribution, which is determined by the distribution of the specific arthropod that carries each disease. Travelers are often infected in one country but exhibit symptoms in another because of the lengthy incubation period for rickettsial diseases.

The specific diagnosis of rickettsioses is most often based on the indirect detection of specific antibodies in the patient's serum, or by detection of rickettsiae in skin biopsy samples. A history of travel, camping, and arthropod bites is particularly important for diagnostic purposes. Doxycycline, tetracycline, and chloramphenicol are the recommended drugs used in the treatment of rickettsioses. Preventive measures include avoiding contact with infected ticks, mites, fleas, lice, and chiggers, and their removal from skin and clothing before transmission of the rickettsia occurs. There is no effective commercial vaccine to prevent these diseases, but several promising experimental vaccines have been developed.

EHRLICHIOSES

Intracellular bacteria in the genus Ehrlichia are the cause of four human diseases that emerged in the later half of the twentieth century (see Table 1). Ehrlichia chaffeensis infects mainly macrophage and monocyte cells, and it causes human monocytic ehrlichiosis (HME). Another isolate, which is not yet officially named, invades human granulocytes and causes human granulocytic ehrlichiosis (HGE). It is closely related to E. ewingii and E. phagocytophila. E ewingii, an organism first associated with illness in dogs, has recently been found to also cause disease in humans. E. sennetsu, the agent of sennetsu ehrlichiosis in humans, is unusual because it is not transmitted by ticks. It appears to be associated with the consumption of raw fish. Several other closely related species of Ehrlichia cause illnesses in dogs, horses, and other animals. In contrast to Rickettsia and Orientia, which grow directly in the cytoplasm of their host cells, ehrlichiae grow in phagosomes where they form clustered, mulberry-like microcolonies called morulae.

Monocytic ehrlichiosis occurs widely in the southern United States. Human granulocytic ehrlichiosis occurs in the United States, Europe, and Africa. Ehrlichiae are transmitted by tick bites, and ticks acquire the bacteria by feeding on infected animals. The American lone star tick is the vector of E. chaffeensis, while the blacklegged tick (deer tick) and western blacklegged ticks are vectors for HGE. The incidence of ehrlichioses correlates with the season of greatest tick activity, peaking from May to July, but the diseases may occur throughout the year in conjunction with human exposure to ticks.

Clinical manifestations of HME and HGE appear after a one- to three-week incubation period and may persist for three to eleven weeks if the diseases are untreated. Ehrlichioses present as a wide range of nonspecific symptoms, including fever, headache, myalgia, gastroenteric dysfunctions, and inflammation of the lymph nodes. Severe cases may be complicated by respiratory insufficiency, neurological symptoms, renal failure, gastrointestinal hemorrhage, and opportunistic viral or fungal infections. Fifty-six to 62 percent of patients require hospitalization, and 2 to 5 percent of patients die.

Clinical diagnoses of ehrlichioses are based on the presence of persisting fever and exposure to ticks in endemic areas. Laboratory diagnosis during the acute stage is achieved by identification of ehrlichial DNA from patient blood samples or detection of cells containing mulberry-like clusters of organisms in peripheral blood smears.

Ehrlichial infections generally respond well to treatment with doxycycline. Ehrlichioses may be prevented by avoidance of tick bites, wearing protective clothing, use of repellents, and prompt removal of attached ticks. Vaccines are not yet available.

Marina E. Eremeeva

(see also: Q Fever; Ricketts, Howard; Typhus, Epidemic; Vector-Borne Diseases; Zoonoses )