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INTRODUCTION

Hemorrhagic fevers caused by viruses are generally rare diseases, but some, like Ebola, have attracted sufficient attention from the press and laypeople that they have become part of our normal vocabulary. The clinical condition known as hemorrhagic fever is quite variable and may result from infection with any one of several different viruses or bacteria. In general, they present as a febrile disease that can progress to manifest some degree of hemorrhage, often in the form of increased capillary permeability, which may lead to death in a significant proportion of those clinically ill. The number of distinct viruses able to cause hemorrhagic fevers continues to grow as we recognize new viruses, such as those associated with hantavirus pulmonary syndrome and the arenaviruses of South America (Table 139-1). All hemorrhagic fever viruses, with the possible exception of dengue viruses, are zoonotic agents that exist in nature in a silent cycle that involves nonhuman vertebrate hosts and often arthropod vectors. Transmission to humans is by the bite of an infectious vector, by small particle aerosol from infectious urine or feces of an infectious host, or through nosocomial transmission, often under conditions where routine safe hospital practices are not being followed. Hemorrhagic fever viruses do not share a common taxonomic origin; they are found among different virus families: Arenaviridae, Hantaviridae, Nairoviridae, Phenuiviridae, Filoviridae, and Flaviviridae.

TABLE 139-1VIRAL HEMORRHAGIC FEVERS

ARENAVIRUSES

Until recently, only three arenaviruses were associated with hemorrhagic fever: Lassa fever caused by Lassa virus of West Africa; Argentine hemorrhagic fever (AHF) caused by Junin virus; and Bolivian hemorrhagic fever (BHF) caused by Machupo virus (MACV).1 In the past decade, however, new pathogenic arenaviruses have been discovered, and it is likely that others will be recognized as humans continue to occupy previously sparsely populated regions of the world (Table 139-2).

TABLE 139-2ARENAVIRUSES KNOWN TO CAUSE HUMAN DISEASE

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