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| __NOTOC__
| | #REDIRECT [[Typhus]] |
| {{SI}}
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| {{CMG}}
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| ==Overview==
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| Many species of Rickettsia can cause illnesses in humans. The term “rickettsiae” conventionally embraces a polyphyletic group of microorganisms in the class Proteobacteria, comprising species belonging to the genera Rickettsia, Orientia, Ehrlichia, Anaplasma, Neo-rickettsia, Coxiella, and Bartonella.
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| ==Pathophysiology==
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| Rickettsial agents are usually not transmissible directly from person to person except by blood transfusion or organ transplantation, although sexual and placental transmission has been proposed for Coxiella. Transmission generally occurs via an infected arthropod vector or through exposure to an infected animal reservoir host.
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| {|
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| |-style="background:silver; color:black"
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| | '''Type of Infection''' || '''Spread'''
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| |-style="background:silver; color:black"
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| | [[Epidemic typhus]] || Body louse
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| |- style="background:silver; color:black"
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| | [[Trench fever]] || Body louse
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| |- style="background:silver; color:black"
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| | [[Murine typhus]] || Flea infested rats
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| |- style="background:silver; color:black"
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| | Cat flea rickettsioses || Fla infested dogs and cats
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| |- style="background:silver; color:black"
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| | [[Scrub typhus]] || Mites
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| |- style="background:silver; color:black"
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| | [[Tick borne rickettsiosis]] || Ticks
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| |- style="background:silver; color:black"
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| | [[Rickettsialpox]] || Mites
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| |- style="background:silver; color:black"
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| | [[Anaplasmosis]] || Ixodes tick
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| |- style="background:silver; color:black"
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| | [[Ehrlichiosis]] || Lone star tick
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| |- style="background:silver;cplor:black"
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| | [[Q fever]] || Infected veterinary animals
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| |- style="background:silver;cplor:black"
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| | [[Cat scratch disease]] || Infected cats
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| |- style="background:silver;cplor:black"
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| | [[Oroya fever]] || Sandflies
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| |}
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| However, sennetsu fever is acquired following consumption of raw fish products. The clinical severity and duration of illnesses associated with different rickettsial infections vary considerably, even within a given antigenic group. Rickettsioses range in severity from diseases that are usually relatively mild (rickettsialpox, cat scratch disease, and African tick-bite fever) to those that can be life-threatening (epidemic and murine typhus, Rocky Mountain spotted fever, scrub typhus and Oroya fever), and they vary in duration from those that can be self-limiting to chronic (Q fever and bartonelloses) or recrudescent (Brill-Zinsser disease). Most patients with rickettsial infections recover with timely use of appropriate antibiotic therapy.
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| Travelers may be at risk for exposure to agents of rickettsial diseases if they engage in occupational or recreational activities which bring them into contact with habitats that support the vectors or animal reservoir species associated with these pathogens.
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| ==Classification==
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| * [[Epidemic typhus]]
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| * [[Trench fever]]
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| * [[Murine typhus]]
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| * [[Cat-Flea rickettsiosis]]
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| * [[Scrub typhus]]
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| * [[Tick-Borne rickettsioses]]
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| * [[Rickettsialpox]]
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| * [[Anaplasmosis]]
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| * [[Ehrlichiosis]]
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| * [[Q Fever]]
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| * [[Cat-Scratch disease]]
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| * [[Oroya fever]]
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| ==Anaplasmosis and Ehrlichiosis==
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| Human ehrlichiosis and anaplasmosis are acute tick-borne diseases, associated with the lone star tick, Amblyomma americanum, and Ixodes ticks, respectively (3,7). Because one tick may be infected with more than one tick-borne pathogen (e.g. Borrelia burgdorferi, the causative agent of Lyme disease, or various Babesia species, agent of human babesiosis), patients may present with atypical clinical symptoms that complicate treatment. Ehrlichioses and anaplasmosis are characterized by infection of different types of leukocytes, where the causative agent multiplies in cytoplasmic membrane-bound vacuole called morulae. Morulae can sometimes be detected in Giemsa-stained blood smears.
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| ==Q Fever==
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| Q fever occurs worldwide, most often in persons who have contact with infected goat, sheep, cat and cattle, particularly parturient animals (especially farmers, veterinarians, butchers, meat packers, and seasonal workers) (1,3). Travelers who visit farms or rural communities can be exposed to Coxiella burnetii, the agent of Q fever, through airborne transmission (via animal-contaminated soil and dust) or less commonly through consumption of unpasteurized milk products or by exposure to infected ticks. These infections may initially result in only mild and self-limiting influenza-like illnesses, but if untreated, infections may become chronic, particularly in persons with preexisting heart valve abnormalities or with prosthetic valves. Such persons can develop chronic and potentially fatal endocarditis.
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| ==Cat-Scratch Disease and Oroya Fever==
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| Cat-scratch disease is contracted through scratches and bites from domestic cats, particularly kittens, infected with Bartonella henselae, and possibly from their fleas. Exposure can therefore occur wherever cats are found. Oroya fever is transmitted by sandflies infected with B. bacilliformis, which is endemic in the Andean highlands.
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| ==Clinical Presentation==
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| Clinical presentations of rickettsial illnesses vary, but common early symptoms, including fever, headache, and malaise, are generally nonspecific. Illnesses resulting from infection with rickettsial agents may go unrecognized or are attributed to other causes. Atypical presentations are common and may be expected with poorly characterized nonindigenous agents, so appropriate samples for examination by specialized reference laboratories should be obtained. A diagnosis of rickettsial diseases is based on two or more of the following:
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| * clinical symptoms and an epidemiologic history compatible with a rickettsial disease,
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| * the development of specific convalescent-phase antibodies reactive with a given pathogen or antigenic group,
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| * a positive polymerase chain reaction test result,
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| * specific immunohistologic detection of rickettsial agent,
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| * isolation of a rickettsial agent. Ascertaining the likely place and the nature of potential exposures is particularly helpful for accurate diagnostic testing.
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| ==Prevention==
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| With the exception of the louse-borne diseases described above, for which contact with infectious arthropod feces is the primary mode of transmission (through autoinoculation into a wound, conjunctiva, or inhalation), travelers and health-care providers are generally not at risk for becoming infected via exposure to an ill person. Limiting exposures to vectors or animal reservoirs remains the best means for reducing the risk for disease. Travelers should be advised that prevention is based on avoidance of vector-infested habitats, use of repellents and protective clothing, prompt detection and removal of arthropods from clothing and skin, and attention to hygiene.
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| Q fever and Bartonella group diseases may pose a special risk for persons with abnormal or prosthetic heart valves, and Rickettsia, Ehrlichia, and Bartonella for persons who are immunocompromised.
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| ==Treatment==
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| Treatments for most rickettsial illnesses are similar and include administration of appropriate antibiotics (e.g., tetracyclines, chloramphenicol, azithromycin, fluoroquinolones, and rifampin) and supportive care. Treatment should usually be given empirically prior to disease confirmation, and the particular antimicrobial agent and the length of treatment are dependent upon the disease and the host. No licensed vaccines for prevention of rickettsial infections are commercially available in the United States.
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| ==References==
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| {{Reflist|2}}
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| {{WH}}
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| {{WS}}
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| [[Category:Disease]]
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| [[Category:Infectious disease]]
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