A rickettsiosis is a disease caused by intracellular bacteria.
Rickettsioses can be divided into a spotted fever group (SPG) and typhus group (TG).
A spotted fever is a type of tick-borne disease which presents on the skin. They are all caused by bacteria of the genus Rickettsia. Typhus is a group of similar diseases also caused by Rickettsia bacteria, but spotted fevers and typhus are different clinical entities.
Typhus, also known as typhus fever, is a group of infectious diseases that include epidemic typhus, scrub typhus and murine typhus. Common symptoms include fever, headache, and a rash. Typically these begin one to two weeks after exposure.
In the past, rickettsioses were considered to be caused by species of Rickettsia.However, scrub typhus is still considered a rickettsiosis, even though the causative organism has been reclassified from Rickettsia tsutsugamushi to Orientia tsutsugamushi .
Rickettsia is a genus of nonmotile, Gram-negative, nonspore-forming, highly pleomorphic bacteria that may occur in the forms of cocci 0.1 μm in diameter, rods 1–4 μm long, or threads of up to about 10 μm long. The term "rickettsia" has nothing to do with rickets, which is a deficiency disease resulting from lack of vitamin D; the bacterial genus Rickettsia was named after Howard Taylor Ricketts, in honour of his pioneering work on tick-borne spotted fever.
Scrub typhus or bush typhus is a form of typhus caused by the intracellular parasite Orientia tsutsugamushi, a Gram-negative α-proteobacterium of family Rickettsiaceae first isolated and identified in 1930 in Japan.
Orientia tsutsugamushi is a mite-borne bacterium belonging to the family Rickettsiaceae and is responsible for a disease called scrub typhus in humans. It is a natural and an obligate intracellular parasite of mites belonging to the family Trombiculidae. With a genome of only 2.4–2.7 Mb, it has the most repeated DNA sequences among bacterial genomes sequenced so far. The disease, scrub typhus, occurs when infected mite larvae accidentally bite humans. Primarily indicated by undifferentiated febrile illnesses, the infection can be complicated and often fatal.
Examples of rickettsioses include typhus, both endemic and epidemic, Rocky Mountain spotted fever, and Rickettsialpox.
Rocky Mountain spotted fever (RMSF) is a bacterial disease spread by ticks. It typically begins with a fever and headache, which is followed a few days later with the development of a rash. The rash is generally made up of small spots of bleeding and starts on the wrists and ankles. Other symptoms may include muscle pains and vomiting. Long-term complications following recovery may include hearing loss or loss of part of an arm or leg.
Rickettsialpox is a mite-borne infectious illness caused by bacteria of the genus Rickettsia. Physician Robert Huebner and self-trained entomologist Charles Pomerantz played major roles in identifying the cause of the disease after an outbreak in 1946 in a New York City apartment complex, documented in "The Alerting of Mr. Pomerantz," a short story by medical writer Berton Roueché.
Organisms involved include Rickettsia parkeri.
Many new causative organisms have been identified in the last few decades.
Most are in the genus Rickettsia, but scrub typhus is in the genus Orientia.
No rapid laboratory tests are available to diagnose rickettsial diseases early in the course of illness, and serologic assays usually take 10–12 days to become positive. Research is indicating that swabs of eschars may be used for molecular detection of rickettsial infections.
Serology is the scientific study of serum and other bodily fluids. In practice, the term usually refers to the diagnostic identification of antibodies in the serum. Such antibodies are typically formed in response to an infection, against other foreign proteins, or to one's own proteins.
An eschar is a slough or piece of dead tissue that is cast off from the surface of the skin, particularly after a burn injury, but also seen in gangrene, ulcer, fungal infections, necrotizing spider bite wounds, spotted fevers and exposure to cutaneous anthrax. The term "eschar" is not interchangeable with "scab". An eschar contains necrotic tissue, whereas a scab is composed of dried blood and exudate.
Doxycycline has been used in the treatment of rickettsial infection.
Boutonneuse fever is a fever as a result of a rickettsial infection caused by the bacterium Rickettsia conorii and transmitted by the dog tick Rhipicephalus sanguineus. Boutonneuse fever can be seen in many places around the world, although it is endemic in countries surrounding the Mediterranean Sea. This disease was first described in Tunisia in 1910 by Conor and Bruch and was named boutonneuse due to its papular skin rash characteristics.
Rickettsia rickettsii is a gram-negative, intracellular, coccobacillus bacterium that is around 0.8 to 2.0 micrometers long. R. rickettsi is the causative agent of Rocky Mountain spotted fever. R. rickettsii is one of the most pathogenic Rickettsia strains. It affects a large majority of the Western Hemisphere and small portions of the Eastern Hemisphere.
Rickettsia akari is a species of Rickettsia which causes rickettsialpox.
Rickettsia conorii is a Gram-negative, obligate intracellular bacterium of the genus Rickettsia that causes human disease called Boutonneuse fever, Mediterranean spotted fever, Israeli tick typhus, Astrakhan spotted fever, Kenya tick typhus, Indian tick typhus, or other names that designate the locality of occurrence while having distinct clinical features. It is a member of the spotted fever group and the most geographically dispersed species in the group, recognized in most of the regions bordering on the Mediterranean Sea and Black Sea, Israel, Kenya, and other parts of North, Central, and South Africa, and India. The prevailing vector is the brown dog tick, Rhipicephalus sanguineus. The bacterium was isolated by Emile Brumpt in 1932 and named after A. Conor who, in collaboration with A. Bruch, provided the first description of boutonneuse fever in Tunisia in 1910.
Leptotrombidium is a genus of mites in the family Trombiculidae, that are able to infect humans with scrub typhus through their bite. The larval form feeds on rodents, but also occasionally humans and other large mammals. They are related to the harvest mites of the North America and Europe.
African tick bite fever (ATBF) is a bacterial infection spread by the bite of a tick. Symptoms may include fever, headache, muscles pains, and a rash. At the site of the bite there is typically a red skin sore with a dark center. Onset usually occur 4–10 days after the bite. Complications are rare, however may include joint inflammation. Some people do not develop symptoms.
North Asian tick typhus, also known as Siberian tick typhus, is a condition characterized by a maculopapular rash.
Flinders Island spotted fever is a condition characterized by a rash in approximately 85% of cases.
Flying squirrel typhus is a condition characterized by a rash of early macules, and, later, maculopapules.
Rickettsia helvetica, previously known as the Swiss Agent, is a bacterium found in Dermacentor reticulatus and other ticks which has been implicated as a suspected but unconfirmed human pathogen. First recognized in 1979 in Ixodes ricinus ticks in Switzerland as a new member of the spotted fever group of Rickettsia, the Rickettsia helvetica bacterium was eventually isolated in 1993. Although R. helvetica was initially thought to be harmless in humans and many animal species, some individual case reports suggest that it may be capable of causing a non-specific fever in humans. In 1997 a man living in eastern France seroconverted to Rickettsia 4 weeks after onset of an unexplained febrile illness. In 2010, a case report indicated that tick-borne R. helvetica can also cause meningitis in humans.
Didier Raoult is a French biologist. He holds MD and Ph.D. degrees and specializes in infectious diseases.
Rickettsia felis is a species of bacterium, the pathogen that causes cat-flea typhus in humans. In cats the disease is known as flea-borne spotted fever. Rickettsia felis also is regarded as the causative organism of many cases of illnesses generally classed as fevers of unknown origin in humans in Africa.
Rickettsia honei is a species of Rickettsia.
Rickettsia sibirica is a species of Rickettsia. This bacterium is the etiologic agent of North Asian tick typhus, which is also known as Siberian tick typhus. The ticks that transmit it are primarily various species of Dermacentor and Haemaphysalis.
Rickettsia japonica is a species of Rickettsia. It can cause Japanese spotted fever.
Rickettsia heilongjiangensis is a species of gram negative Alphaproteobacteria, within the spotted fever group, being carried by ticks. It is pathogenic.
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