Viral hemorrhagic fever

Viral hemorrhagic fevers (VHFs) are a group of diseases that share the ability to damage multiple organ systems, among them the vascular system of blood vessels. Vascular damage, and in some cases damage to clotting mechanism, cause frequent bleeding, thus the general term hemorrhagic fever (HF). While there are some common biological features among the causative viruses, the group is characterized more by the nature of the disease presentation than the classification of the pathogen.

Not all fevers accompanied by bleeding are VHF, although until a VHF is excluded, the potential public health risk requires assuming that the cause is the most contagious and dangerous form consistent with the presentation. For example, scrub typhus, caused by the bacterium Orientia tsutsugamushi (formerly Rickettsia tsutsugamushi), can present as a HF.

Due to their infectivity, general lack of treatment programs, and poor understanding of reservoirs, many VHFs are listed in the Select Agent Program. Many need to be handled at Biosafety Level 4.

Characteristics of the viruses

Several different families of virus cause VHFs. They share the property of being RNA viruses with a lipid (fatty) coat.

While the focus of this article is VHF, the list below shows that not all species of the families cause HF; some species can present as a non-HF (e.g., dengue) or HF (e.g., dengue HF). The recognized families are:

• arenaviruses (genus arenavirus, family Arenaviridae)
  • HF: Argentine/Junin, Bolivian/Machupo, Flexal, Lassa, Guanarito, Sabia, Venezuelan
  • non-HF: Flexal virus, Lymphocytic choriomeningitis virus
• bunyaviruses (genus bunyavirus, family Bunyaviridae
  • HF: Crimean-Congo, hemorrhagic fever with renal syndrome (HFRS)
  • non-HF: Hantavirus pulmonary syndrome (HPS), Rift Valley fever (RVF)
• filoviruses (genus filovirus, family Filoviridae)
  • HF: Marburg, Ebola
  • non-HF: none identified
• flaviviruses (genus flavivirus, family Flaviviridae)
  • HF: Dengue HF, Omsk HF, Yellow fever (hemorrhagic)
  • non-HF: Dengue fever, Central European tick-borne encephalitis, Far Eastern tick-borne encephalitis, Kyasanur Forest disease, Hepatitis C, West Nile virus, Yellow Fever Virus

Epidemiology

At the species level, they are limited to a geographic level, and on an animal reservoir. Some can transmit from human to human as well as from animal to human. Not all reservoirs have been identified.

Outbreaks in humans are unpredictable.

While none is definitely known to have been weaponized, some VHFs do have potential as biological weapons.

Prevention

When the reservoir is known, extermination, sanitation and barriers are important.

While a yellow fever vaccine has long been available, other vaccine development recently has accelerated. There has been some success with Argentine HF, also known as Junin, It may also be effective against Bolivian/Machupo.

Research trials have been published on vaccines for Ebola and Marburg.

Treatment

For most of the VHF, the treatment is supportive, with barrier precautions to avoid spread. Ribavirin is helpful for Lassa fever. Plasma from recovering patients has helped some patients with Argentine hemorrhagic fever.

Given that a number of these diseases occur in underdeveloped countries where full barrier precautions may not be possible, the World Health Organization (WHO), with the CDC, has prepared a guide, focused on Africa, for what can be done with limited resources.