Viral Hemorrhagic Fevers (VHFs)

What Is It?

VHFs refer to a group of illnesses that are caused by several distinct families of viruses. In general, the term "viral hemorrhagic fever" is used to describe a severe multi-system syndrome, where multiple organ systems in the body are affected.

VHFs include four families of viruses: filiviruses such as the Ebola and Marburg viruses, arenaviruses such as Lassa, bunyavirus such as Rift Valley Fever and flaviviruses such as yellow fever and dengue. They can all cause serious, life-threatening illnesses. Some, including Ebola, Marburg and Lassa, are contagious. Although the Ebola virus gained notoriety in various films such as Outbreak and books, VHFs aren't expected to be prime bioweapon candidates since people die so quickly from them and often don't get a chance to infect others.

During World War II, the Japanese army fed botulinum toxin to prisoners of war in Manchuria, with lethal results.

How Is It Spread?

VHFs naturally occur in humans only after contact with an infected insect, rodent or larger mammal. Transmission can happen via touching fecal matter, receiving an insect bite or handling contaminated meat. It's possible VHFs can be manufactured for aerosol dissemination but the bacterium generally don't fare well in this form.

What Are the Symptoms of Exposure?

Characteristically, the overall vascular system is damaged, and the body's ability to regulate itself is impaired. These symptoms are often accompanied by hemorrhage (bleeding); however, the bleeding is itself rarely life-threatening. While some types of hemorrhagic fever viruses can cause relatively mild illnesses, many of these viruses cause severe, life-threatening disease.

All types in severe cases can cause hemorrhagic syndromes that cause severe internal and external bleeding in places such as internal organs, under the skin and from the eyes, nose, mouth and ears. Symptoms generally include high fever, dizziness, muscle aches and exhaustion. The first symptoms may be felt from two days to three weeks after exposure. Advanced symptoms include shock, nervous system malfunction, seizures and coma. Fatality rates range from 90 percent for Ebola to 1 percent for Lassa.

How Is It Treated?

Treatment is available for some VHFs, but not all. In the event of an outbreak, routine infection control procedures, isolation and decontamination are usually enough to stop transmission. Treatments vary depending on which virus a victim has. No treatments or vaccines exist for Ebola or Marburg, but therapy can prevent shock and help organs function. Antiviral drug ribavirin can treat some VHFs fairly well if given early on. A yellow fever vaccine is available. Other treatments are under development.

Who Has It/Where Can It Be Found?

The most worrisome VHFs, such as Marburg and Ebola, are hard to acquire from the wild because their natural host is unknown and outbreaks are rare. VHFs are studied in some labs, mainly high-security ones. Research on Ebola and several others was done by the Soviet Union before its biowarfare program was dismantled.

Experts warn that because microbe collections in Russia, Kazakhstan, Georgia and Uzbekistan are not adequately secured, terrorist groups or states might be able to steal or otherwise obtain weaponized strains of plague, tularemia and VHFs.

During a 1992 trip to Zaire, operatives from the Japanese doomsday cult Aum Shinrikyo tried unsuccessfully to acquire samples of the Ebola virus, and some experts think that an Iraqi viral strain code-named "Blue Nile" may be Ebola.