What are Viral Hemorrhagic Fevers?

Viral hemorrhagic fevers (VHF) are a group of illnesses caused by four distinct families of viruses: arenaviruses, filoviruses, bunyaviruses, and flaviviruses. They are all RNA viruses and are zoonotic (natural reservoir is an arthropod or another animal host). Transmission to humans occurs by contact with rodent feces, urine, saliva, blood, from a mosquito or tick bite or contact with infected animal or human. All types of VHF are characterized by fever and bleeding disorders. The viruses can progress to high fever, shock, internal or external bleeding, and even death. [1]

Typical Viral Hemorrhagic Fever Symptoms
Typical Viral Hemorrhagic Fever Symptoms

Types of Viral Hemorrhagic Fevers: [2]

Major worldwide hemorrhagic fever viruses
Major worldwide hemorrhagic fever viruses
  • Bunyaviridae: a family of negative stranded, enveloped RNA viruses that are generally found in arthropods (ticks and mosquitoes) or rodents. Examples of this type of VHF include Rift Valley Fever, Crimean-Congo fever and Hantavirus fever.
    • Crimean Congo Fever: is a tick born disease with a 30% mortality rate, outbreaks are usually attributed to handling infected animals or people. Symptoms include acute kidney failure, shock, nosebleeds, swollen liver, and ecchymosis (see below)

A patient with Crimean-Congo hemorrhagic fever with profound ecchymosis
A patient with Crimean-Congo hemorrhagic fever with profound ecchymosis

  • Flaviviridae: a family of viruses that are primarily spread through arthropod vectors (mainly ticks and mosquitoes). Viruses included in this family are yellow fever, dengue fever and Omsk fever.
    • Dengue Fever: is a mosquito borne viral infection that causes flu like illness and can possibly develop lethal complications
Patient with dengue hemorrhagic fever has a large subcutaneous hemorrhage on upper arm.
Patient with dengue hemorrhagic fever has a large subcutaneous hemorrhage on upper arm.
  • Arenaviridae:is a genus of viruses that infects rodents and occasionally humans. The risk of getting the Arenavirus infection for humans is related to age, race, or sex within the degree of contact with the dried rodent excrement.
    • Lassa Fever: is an acute viral hemorrhagic fever caused by the lassa virus. It is spread to humans through contact with infected rodents. Symptoms include nausea, vomiting, difficulty swallowing, cough, encephalitis, seizures and facial mucosal bleeding (see below)
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  • Filoviridae: is a family of viruses that can spread from bats to humans, examples of this type of virus are Ebola and hemorrhagic fever.
    • Ebola: The Ebola virus can cause severe viral haemorrhagic fever (VHF) outbreaks in humans with a case fatality rate of up to 90%. Ebola is introduced into the human population through close contact with the blood, secretions, organs or other bodily fluids of infected animals. Ebola is often characterized by the sudden onset of fever, intense weakness, muscle pain, headache and sore throat.
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  • The first arenavirus was isolated in 1933 during an outbreak of St. Louis Encephalitis virus.
  • In 1958, the Junin virus was isolated in the plains of Argentina in agricultural workers. It was the first arenavirus found to cause hemorrhagic fever. Others soon followed including Machupo virus in Bolivia in 1963 and Lassa virus in Nigeria in 1969.
  • Since 1956, a new arenavirus has been discovered every one to three years, but not all cause hemorrhagic fever.
  • River Valley Fever virus was first isolated in 1930 from an infected newborn lamb, as part of investigation of a large epizootic of disease causing abortion and high mortality in sheep in Egypt.
  • Crimean-Congo Hemorrhagic Fever virus was first recognized in the Crimean peninsula located in southeastern Europe on the northern coast of the Black Sea in the mid-1940s, when a large outbreak of severe hemorrhagic fever among agricultural workers was identified. The outbreak included more than 200 cases and a case fatality of about 10%.
  • The discovery of hantaviruses traces back to 1951 to 1953 when United Nations troops were deployed during the border conflict between North and South Korea.
  • Marburg virus was first isolated in 1967 from several cases of hemorrhagic fever in European laboratory workers in Germany and former Yugoslavia working with tissues and blood from African green monkeys imported from Uganda.
  • Ebola virus was first reported simultaneously in Zaire and Sudan in 1976 when two distinct subtypes were isolated in two hemorrhagic fever epidemics.
  • In 1994, a fourth subtype of Ebola was isolated from a animal worker in Côte d'Ivoire who had preformed a necropsy on an infected chimpanzee. Scattered outbreaks have occurred periodically with latest being an outbreak of Ebola in the Republic of the Congo in 2003.
  • Yellow Fever was first described in 1648 in Yucatan. It later caused huge outbreaks in tropical Americas in 17th, 18th, 19th, and 20th century. The French failed to complete the Panama Canal because their work force was decimated by Yellow Fever.
  • Yellow Fever virus was first flavivirus isolated in 1927 and the first virus to be proved to be transmitted by an arthropod vector. Dengue virus which was also found to be transmitted by an arthropod was isolated in 1943. Major outbreaks of dengue with hemorrhagic fever have occurred in Australia in 1897, Greece in 1928, and Formosa 1931. [3]

History of Bioterrorism: Viral Hemorrhagic Fevers

Role in Bioterrorism

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The former Soviet Union developed the Marburg virus for use as a weapon, and conducted research on Ebola, Lassa, Rift Valley fever, yellow fever and New World arenaviruses. The U.S. has done research on all of these viruses, except Marburg and Ebola. North Korea is believed to have developed the yellow fever virus as a weapon. In 1999, the CDC classified the VHF's as category A bioweapon agents, based on the potential to cause widespread illness and death, ease of dissemination or person to person transmission, potential for major public health impact, and requirement of special action for public health prepardness.

What VHF's are the biggest threat? [4]

Viral hemorrhagic fever viruses can be very infectious, and outbreaks of VHF can result in high death rates. The two viruses considered to be the greatest bioterrorism threats are Ebola and Marburg, the two members of the filovirus family, which are categorized as category A bioweapon agents. These viruses characteristically cause high mortality and morbidity, are person to person spread, are highly infectious at a low dose by the aerosol route, are stable in the environment, and large-scale production is feasible. Attempts have been made to use these viruses as weapons by aerosolizing infected body fluids or rodent excrement.


There are no vaccines that exist that can protect against VHF, with the exception of yellow fever and Argentine hemorrhagic fever. Therefore, prevention efforts must concentrate on avoiding contact with host species. If those prevention methods fail, and VHF does occur, the focus is put on preventing further transmission from person to person.

Disease prevention efforts include:

  • controlling rodent populations;
  • discouraging rodents from entering or living in homes or workplaces;
  • encouraging safe cleanup of rodent nests and droppings.
For hemorrhagic fever viruses spread by arthropod vectors, prevention efforts often focus on community-wide insect and arthropod control. In addition, people are encouraged to use insect repellant, proper clothing, bed nets, window screens, and other insect barriers to avoid being bitten.
For those hemorrhagic fever viruses that can be transmitted from one person to another, avoiding close physical contact with infected people and their body fluids is the most important way of controlling the spread of disease. [1]

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[1] “Viral Hemorrhagic Fever” CDC. N.p., N.d. Web. 1 Mar. 2014 http://www.cdc.gov/ncidod/dvrd/spb/mnpages/dispages/vhf.htm
[2] "Hemorrhagic Fevers, Viral" WHO. N.p., N.d. Web. 10 Mar. 2014
[3] “Viral Hemorrhagic Fever” The Center for Food Security and Public Health. Iowa State University N.D. Web. 1 Mar. 2014. http://www.cfsph.iastate.edu/DiseaseInfo/ppt/ViralHemorrhagicFever.ppt
[4] “What You Need to Know About Viral Hemorrhagic Fevers and Bioterrorism” Texas State Department of State Health Services. Aug. 2004. Web. 1 Mar. 2014. https://www.dshs.state.tx.us/preparedness/factsheet_vhf.pd