(hĕm´´Әrăj'ĭk), any of a group of viral diseases characterized by sudden onset, muscle and joint pain, fever, bleeding, and shock from loss of blood. Bleeding occurs in the form of leakage from capillaries in the internal organs and the skin and mucous membranes. The causative viruses may be transmitted to humans by insects, ticks, or rodents, but in the case of the African hemorrhagic fevers Ebola and Marburg the animal carrier is unknown. In addition to Ebola and Marburg, well-known hemorrhagic fevers include hantavirus, Lassa fever, yellow fever, and a severe form of dengue called dengue hemorrhagic fever (see dengue fever; see also Ebola virus).
Ebola and Marburg are closely related, newly emergent viruses that have in recent years caused epidemics in central Africa, with very high rates of mortality. Hantavirus occurs in many different parts of the world and is spread to humans from field rodents via microscopic bits of their excretions that get into the air and are inhaled. It was originally known as a disease of Asia and Europe that primarily attacked the kidneys, but a more deadly pulmonary form of hantavirus infection has more recently caused numerous fatalities in the United States, Chile, and other countries. Lassa fever, also spread to humans from rodent excretions, occurs primarily in W Africa. Closely related to the Lassa virus are the Junin and Machupo viruses, which have caused outbreaks of hemorrhagic fever in South America. Crimea-Congo hemorrhagic fever, which is found primarily in Africa, SW and central Asia, and SE Europe, and Rift Valley fever, which can result in hemorrhagic fever in humans and is found in Africa and the Arabian Peninsula, are typically transmitted to humans from livestock by ticks or mosquitoes respectively or by contact with fluids or tissues from infected animals. Yellow fever, transmitted by the bite of a mosquito, still occurs in tropical areas despite largely successful control efforts. Dengue hemorrhagic fever, also spread by mosquitoes, has in recent years caused many fatalities among children in tropical countries.
There is usually no specific treatment to combat the viruses that cause hemorrhagic fevers. One exception is the drug ribavirin, which has been effective in treating Lassa fever and has also been used to treat a form of hantavirus infection and Crimean-Congo hemorrhagic fever. Treatment generally consists of such supportive measures as the replacement of lost blood, the maintainence of fluid balance, and the alleviation of symptoms. Survival depends largely upon the virulence of the virus strain and the quality of treatment. An experimental vaccine for Ebola was developed and used in a limited manner against the strain that caused the 2013–15 West African outbreak, but its long-term effectiveness is unclear.