What is viral hemorrhagic fever?

Viral hemorrhagic fevers (VHFs) are illnesses caused by several distinct families of viruses. The term "viral hemorrhagic fever" is used to describe a severe condition that affects several organ systems in the body. Typically, the vascular system is damaged, so the body is unable to regulate itself normally. Another characteristic of VHFs is hemorrhaging (bleeding), though the bleeding in itself is rarely life-threatening.

VHFs are divided into four categories: arenaviruses, filoviruses, bunyaviruses, and flaviviruses. The categories are divided by the geographical areas where the illnesses develop.

Common characteristics of all VHFs are:

• They are covered with a fatty (lipid) coating.
• Their survival is dependent on an animal or insect host
• They first infect hosts and only spread to humans when humans come into contact with the host
• Their outbreaks are not easily predicted.
• They  usually have no cure or established drug treatment

Nearly all viral hemorrhagic fevers live inside animal or insect hosts; rodents, ticks and mosquitoes are common carriers. Hosts of some viruse-Ebola and Marbug, for example-are unknown.

Hemorrhagic fever viruses are good candidates for use as bioterrorism agents because they can be packaged and diffused by aerosol. Nonhuman primates have been infected by aerosolized Ebola, Marburg, Lassa, and New World arenaviruses, and the former Soviet Union and Russia allegedly produced large quantities of Ebola, Lassa, and New World arenavirus until 1992 .  VHFs used as bioterrorism agents have the potential to sicken and kill many people.  Viruses can be transmitted from person to person, and because few treatments or vaccines exist.

What are the symptoms of viral hemorrhagic fever?

Viral hemorrhagic fever's symptoms vary depending on the type of virus, but initial signs and symptoms often include fever, fatigue, dizziness, muscle aches, loss of strength, and exhaustion. Patients with severe cases of VHFs often show signs of bleeding under the skin, bleeding in internal organs, or bleeding from the mouth, eyes, or ears.

Severely ill patient cases may also show shock, nervous system malfunction, coma, delirium, and seizures. Some types of VHF are associated with renal (kidney) failure.

Where is viral hemorrhagic fever prevalent?

Viral hemorrhagic fevers occur throughout the globe, but the specific viruses are restricted to the geographical area where their hosts live.

Rodents that carry New World arenaviruses live in geographically restricted areas, so the risk of getting those VHFs is restricted to those regions.

Other hosts and their viruses have more expanded appearances. Rodents that carry forms of hantavirus pulmonary syndrome can be found throughout North and South America, and the rodents that carry viruses causing hemorrhagic fever with renal syndrome (HFRS) live in Europe and Asia.  The common can be found almost anywhere in the world, as can the HFRS-causing Seoul virus it carries.

Usually people become infected with viral hermorrhagic fevers in the areas where their hosts live, though, on occasion, the host carries the virus from its native habitat to other lands.  Outbreaks of Marburg hemorrhagic fever, in Marburg and Frankfurt, Germany, and in Yugoslavia, occurred when laboratory workers handled imported monkeys infected with Marburg virus.  Humans may also carry the virus, as was the case when a physician treating patients with Ebola in Gabon become infected and later transmitted the virus to a nurse in South Africa. A recent increase in worldwide travel has increased the possibility that viruses will show up in places they've never existed before.

How are hemorrhagic fever viruses transmitted?

Humans usually contract VHFs when they come into contact with rodent urine, feces, saliva, or other body excretions or when they're bit by a mosquito or tick. Occasionally, hosts infect animals, which later transmit the virus to humans who care for or slaughter them.

Some viruses can be transmitted from an infected humans other humans; Ebola, Marburg, Lassa and Crimean-Congo hemorrhagic fever viruses are examples. This transmission may occur through close contact with people or their body fluids.

How is viral hemorrhagic fever treated?

In most cases, there is no treatment available for victims of VHFs.  The anti-viral drug Ribavirin, has been effective in treating some individuals with Lassa fever or HFRS, and plasma has helped some patients with Argentine hemorrhagic fever. With the exception of yellow fever Argentine hemorrhagic fever, no vaccines have been developed, and no existing vaccines can protect against these diseases.

How can I protect myself from viral hemorrhagic fever?

Because no vaccines exist to combat most viral hemorrhagic fevers, the best way to protect yourself is to avoid contact with host species. Support measures to control rodent and insect populations, and try to keep them out of your home. If you are around someone with viral hemorrhagic fever, isolate the infected person, use protective clothing and be sure to disinfect and sanitize properly.

To find out more about viral hemorrhagic fever, check out the Centers for Disease Control web site, http://www.cdc.gov/search.do?action=search&queryText=viral+hemorrhagic+fever, or ask your doctor.