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Which typhus fever?

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Diagnosis, Differential↗

The typhus group.

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Humans↗

Serologic survey of spotted fever group rickettsiosis on Hainan Island of China.

A serosurvey for antibodies to Rickettsia japonica was conducted on Hainan Island of China. Serum specimens were collected from 1,030 outpatients at hospitals in different parts of the island regardless of their diagnosis. Only two among 538 serum specimens collected in Baoting and Tongshi counties, located in the southern part of the island, were demonstrated to contain antibodies reactive with R. japonica at a high dilution. The specimens also reacted with R. rickettsii at the same titer as with R. japonica. These two specimens reacted with other pathogenic spotted fever group (SFG) rickettsiae to a lesser extent. On the other hand, the specimens were shown to possess antibodies reactive with R. typhi at a significantly lower dilution or were not reactive at all. The findings suggested the occurrence of an SFG rickettsiosis on Hainan Island. More than half of the serum specimens collected from patients with suspected rickettsial infections in the southern area were found to contain IgM and IgG antibodies to R. typhi, indicating a high incidence of murine typhus.

Antibodies, Bacterial↗

Cloning and sequencing of the gene encoding the candidate HtrA of Rickettsia typhi.

We screened a phage library of Rickettsia typhi with a polyclonal antiserum to clone genes which encode immunogenic proteins of R. typhi. Among several clones obtained, one clone codes for a 466-amino-acid protein similar to the heat-shock protein, HtrA. The deduced rickettsial HtrA contains a putative signal peptide sequence at the N-terminus, a serine protease-like domain, and two PDZ domains. The recombinant protein of rickettsial HtrA reacted with sera from patients with murine typhus and tsutsugamushi disease. We suggest that this gene and its recombinant protein would be valuable for the immunologic diagnosis of rickettsial diseases.

Amino Acid Sequence↗

[Rickettsioses].

Species of the genus Rickettsia are small, obligate intracelular, gramnegative bacteria, many of which are considered nowadays a paradigm of emergent pathogens. With the exception of R. prowazekii, they are maintained in the natural environment through a cycle involving different hosts (mainly mammals), and arthropod vectors (in general ticks, and fleas); humans are affected only by incidental transmission due to arthropod bites. The common pathogenesis of these diseases lie on the predominantly infection of endotelial cells, that determines the development of multisistemic small vessel vasculitis, which may affect lungs (interstitial pneumonitis), heart (miopericarditis), skin (rash), central nervous system (meningoencephalitis), as well as liver, and kidneys. They are classified in two groups: spotted-fever group, and typhus group rickettsia. In Spain the most prevalent rickettsioses of both groups are mediterranean spotted fever (caused by R. conorii), and murine typhus (caused by R. typhi), respectively. This review focuses mainly in these two diseases, and also in other rickettsioses of interest due to their recently emergence or reemergence (R. slovaca, R. africae, R. prowazekii, R. felis), or to their high incidence in other areas (R. rickettsii, Orientia tsutsugamushi).

Animals↗

Epidemiology of rickettsial diseases.

Rickettsial diseases have a diversity of epidemiologic characteristics reflective of the variety of ecologic situations in which the obligate intracellular bacteria are transmitted to humans. For the spotted fever group (SFG) rickettsiae, Rickettsia typhi, R. tsutsugamushi, Coxiella burnetii, and the human ehrlichial agent, humans are a dead-end host who plays no role in the maintenance of the organism in nature. All rickettsioses exist as zoonoses. Moreover, all rickettsiae are found in infected arthopods, which generally serve as the natural hosts and can transmit the infection to the next generation of ticks, mites, chiggers, or fleas. From our anthropocentric viewpoint, Q fever aerosol infection from parturient animals and Brill-Zinsser disease ignited epidemics of louse-borne epidemic typhus are exceptions. However, silent cycles of C. burnetii in ticks and R. prowazekii in the flying squirrel flea may have maintained these agents in transovarial or enzootic cycles for eons before humans and their domestic animals arrived on the scene. Thus, the epidemiology of rickettsial diseases must be recognized as an unfortunate aberration of the rickettsial economy. Several excellent reviews of rickettsial ecology contain a wealth of useful information.

Animals↗

[Serological approach to the occurrence of rickettsioses in the Central African Republic].

A serosurvey for evidence of human rickettsial infections was carried out in the Republic of Central Africa on 144 sera by indirect immunofluorescence (IIF) and microagglutination tests (MA). There was no serological evidence of epidemic typhus and only two sera were positive for murine typhus. Approximately 15% of the surveyed population was serologically positive by MA for R. conorii antibodies. However, 48% of this population had spotted fever group antibodies as detected by IIF but were negative in MA for R. conorii, R. rickettsii and R. akari antibodies. These sera with high titers in IIF and negative in MA lead us to believe that in Central Africa there are rickettsiae pathogenic for man that are related to the Spotted Fever group and are yet to be identified.

Agglutination Tests↗