I.

Introduction

Hemorrhagic Fever, common name for a group of acute viral diseases, the symptoms of which usually begin with fever and muscle aches and progress to dizziness, collapse, swelling, and shock. Depending upon the particular virus, hemorrhagic fevers may progressively produce respiratory problems, internal bleeding, kidney problems, and death. Most hemorrhagic fever viruses have only been recognized within the past 50 years and new hemorrhagic fever viruses are identified each year.

Hemorrhagic fevers are caused by more than 20 known viruses from four different families: Arenaviridae, Bunyaviridae, Flaviviridae, and Filoviridae. The viruses are often named for the region, town, or geographic feature where they were first identified. The Arenaviridae family includes Lassa (see Lassa Fever), Junín (the cause of Argentine hemorrhagic fever), Machupo (the cause of Bolivian hemorrhagic fever), and Guanarito (the cause of Venezuelan hemorrhagic fever) viruses. While these viruses are usually transmitted to humans by rodents, human-to-human transmission can occur, particularly with Lassa fever.

The Bunyaviridae family includes Rift Valley fever virus, a notable mosquito-borne virus in Africa, and the hantaviruses. During the Korean War (1950-1953), thousands of American troops developed mysterious symptoms including high fevers, headaches, internal bleeding, and kidney failure. It was not until 1976 that the viral cause of the disease was identified as Hantaan virus, a hantavirus. The disease is now recognized as one of a group of diseases called hemorrhagic fever with renal syndrome. A related virus, named Sin Nombre, was discovered in the United States in 1993. Sin Nombre was found to cause severe respiratory distress syndrome, which starts with flulike symptoms followed by respiratory failure and often death. The original 1993 outbreak struck New Mexico, Colorado, Arizona, and Utah, killing 58 people. Today, Sin Nombre virus is known to exist in deer mice in more than 30 American states, and similar viruses have been found in South America and Canada.

The Flaviviridae family includes the viruses that cause dengue hemorrhagic fever and yellow fever. These viruses are transmitted by the bites of infected mosquitoes. Dengue hemorrhagic fever occurs mostly in children under the age of ten who live in areas where milder dengue fever is common. Dengue fever resembles the flu with fever, tiredness, and muscle aches from which patients recover in about a week, but dengue hemorrhagic fever is also accompanied by internal hemorrhaging and shock and may cause death. Yellow fever, found mostly in Africa and South America, is spread in urban areas by the bite of the mosquito, Aedes aegypti. In the jungle, yellow fever is carried by various mosquito species and monkeys that live high in the tree canopy, the uppermost layer of spreading branches in the forest.

The Filoviridae family includes Marburg and four strains of Ebola viruses. Ebola hemorrhagic fever was first recognized in Zaire (now the Democratic Republic of the Congo, or DRC) and the Sudan in 1976 where it caused deadly epidemics. The virus reemerged in Kikwit, Zaire, in 1995 and Gabon in 1996, causing additional, frightening epidemics. Persons infected with the Ebola virus experience headache, high fever, muscle pain, vomiting, and internal and external bleeding. The mortality rate of Ebola hemorrhagic fever ranges from 50 to 90 percent.