TAILIEUCHUNG - Chapter 167. Rickettsial Diseases

The rickettsiae are a heterogeneous group of small, obligately intracellular, gram-negative coccobacilli and short bacilli, most of which are transmitted by a tick, mite, flea, or louse vector. Except for louse-borne typhus, humans are incidental hosts. Among rickettsiae, Coxiella burnetii, Rickettsia prowazekii, and R. typhi have the well-documented ability to survive for an extended period outside the reservoir or vector and to be extremely infectious: inhalation of a single Coxiella microorganism can cause pneumonia. High infectivity and severe illness after inhalation make R. prowazekii, R. rickettsii, R. typhi, R. conorii, and C. burnetii bioterrorism threats. . | Chapter 167. Rickettsial Diseases The rickettsiae are a heterogeneous group of small obligately intracellular gram-negative coccobacilli and short bacilli most of which are transmitted by a tick mite flea or louse vector. Except for louse-borne typhus humans are incidental hosts. Among rickettsiae Coxiella burnetii Rickettsia prowazekii and R. typhi have the well-documented ability to survive for an extended period outside the reservoir or vector and to be extremely infectious inhalation of a single Coxiella microorganism can cause pneumonia. High infectivity and severe illness after inhalation make R. prowazekii R. rickettsii R. typhi R. conorii and C. burnetii bioterrorism threats. Clinical infections with rickettsiae can be classified according to 1 the taxonomy and diverse microbial characteristics of the agents which belong to six genera Rickettsia Orientia Ehrlichia Anaplasma Neorickettsia and Coxiella 2 epidemiology or 3 clinical manifestations. The clinical manifestations of all the acute presentations are similar during the first 5 days fever headache and myalgias with or without nausea vomiting and cough. As the course progresses clinical manifestations including occurrence of a macular maculopapular or vesicular rash eschar pneumonitis and meningoencephalitis vary from one disease to another. Given the 12 etiologic agents with varied mechanisms of transmission geographic distributions and associated disease manifestations the consideration of rickettsial diseases as a single entity poses complex challenges Table 167-1 . Table 167-1 Features of Selected Rickettsial Infections Disease Organis Transmi Geogra Incub Dura Ra Esc Lymphade m ssion phic ation tion sh har nopathy Range Perio Day d s Days Rocky Rickettsia Tick bite United 2-14 10- 90 1 Mountain rickettsii Dermace States 20 spotted ntor fever andersoni D. United variabilis States Amblyom Central ma South cajennens Americ e A. a aureolatu m Rhipicep Mexico halus sanguine United us States Mediterra R.

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