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What are Viral Hemorrhagic Fevers?

Viral hemorrhagic fevers (VHFs) refer to a group of illnesses that are caused by several different viruses. In general, the term "viral hemorrhagic fever" is used to describe a severe viral infection of many organ systems in the body.  Symptoms vary since over 12 different viruses are included in this group. However, the blood vessels are usually damaged causing leakage of the blood into the organs and into the membranes surrounding the eyes (whites of eyes become red), nose (nose bleed), intestines (blood in stools), stomach (vomit blood), bladder (blood in urine) and/or lungs (cough up blood). Frequently, small pinpoint bleeding into the skin and in the roof of the mouth can be seen (petechiae). Some types of hemorrhagic fever viruses can cause relatively mild illnesses (ex. Dengue fever virus). Others can cause severe, life-threatening disease (ex. Ebola and Marburg viruses) (9, 47, 62, 65).

The VHF viruses belong to 4 different families of viruses; Filoviridae (Ebola and Marburg), Arenaviridae (Lassa, Machupo, Junin, Guanarito, and Sabia), Bunyaviridae (Crimean-Congo hemorrhagic fever virus, Rift Valley fever virus, and Hantaviruses) and Flaviviridae (Dengue, Yellow fever, Omsk hemorrhagic fever and Kyasanur forest disease).

They are all RNA viruses, and are covered with a lipid envelope (Table 3). Their survival is dependent on an animal or insect host, called the reservoir. The viruses are geographically restricted to the areas where their host lives. Humans are not the reservoir for any of these viruses. Humans are infected when they come into contact with infected hosts. Mosquitoes or ticks can in some cases transmit the virus from the reservoir host to humans. Animal reservoirs are generally rats and mice, but domestic livestock, monkeys, and other primates may also serve as hosts. With some of these viruses, after the accidental transmission from the host, humans can transmit the virus to one another. Person-to-person transmission may occur through direct contact with infected patients, their blood, or their secretions (saliva, nasal mucus) and excretions (stools, urine). Human cases or outbreaks of hemorrhagic fevers caused by these viruses occur sporadically and irregularly. Usually these outbreaks are associated with destruction of the region in which the hosts live (flooding of the Rift Valley) or intrusion of humans into previously uninhabited areas. With a few exceptions, there is no cure or established drug treatment for VHFs. 

If you include all the VHF viruses these diseases are distributed over most of the world. However, because each virus is associated with one or more particular host, the virus and the disease it causes are usually seen only where the hosts live. Some hosts, such as rodents that carry several of the New World arenaviruses, live in geographically restricted areas. Therefore, the risk of getting VHFs caused by these viruses is restricted to those areas. Other hosts range over continents, such as the rodents that carry viruses which cause various forms of hantavirus pulmonary syndrome (HPS). These hosts are present in North and South America. Other rodents carry viruses which cause hemorrhagic fever with renal syndrome (HFRS) are found in Europe and Asia.

The overall incubation period for VHFs ranges from 2 to 21 days. Patients initially have a high fever, headache, tiredness, joint aches, muscle aches, nausea, abdominal pain, and nonbloody diarrhea that usually last about a week. Filoviruses, Rift Valley fever, and flaviviruses are characterized by an abrupt onset, while arenaviruses have a more gradual onset of symptoms. 

Early signs typically include fever, low blood pressure, a low heart rate, a high respiration rate, conjunctivitis and sore throat. Most diseases are associated with the skin becoming red or a skin rash, but the specific characteristics of the rash vary with each disease. Later, patients may show signs of progressive bleeding, such as skin petechiae, petechiae in the mouth, and bleeding in the conjunctiva; blood in the urine; vomiting blood; and dark black stools indicating bleeding in the intestines (melena). Due to the blood loss the patient may develop extremely low blood pressure and go into shock. Infection of the brain may present with delirium, convulsions, or coma. Patients with infection of the brain more commonly result in death.  

Why are VHF viruses attractive BW?

Hemorrhagic fever viruses have been studied as potential BW by the USSR and the U.S. (55). The former Soviet Union and Russia researched use of Marburg, Ebola, Lassa, and New World arenaviruses (Junin and Machupo) until 1992. Yellow fever and Rift Valley fever viruses were developed as weapons by the U.S. offensive biological weapons program prior to its termination in 1969. The Japanese terrorist cult Aum Shinrikyo unsuccessfully attempted to obtain Ebola virus as part of an effort to create biological weapons (5). Many of the viruses can also be transmitted from person-to-person. 

Laboratory Diagnosis

Blood is taken and would have to be sent to high-containment (BSL-4) laboratories equipped to handle these viruses. The laboratories use a variety of tests to look for specific viral protein or RNA in the blood.

Treatment

The most common method is to place the patient in a hospital and give them supportive care. Sometimes the care must be very aggressive and will include intravenous administration of fluids and various medications/blood components to raise the blood pressure and stop the bleeding. In severe cases of respiratory distress mechanical ventilation may be required. There are no antiviral drugs approved by the U.S. Food and Drug Administration for treatment of HFVs. However, some have found ribavirin to be helpful in treating Arenaviridae and Bunyaviridae infections but it is not useful in treating Filoviridae or Flaviviridae infections. 

Prevention

There is only one vaccine available to civilians and it is effective in preventing Yellow fever. The Yellow fever vaccine is produced in limited quantities, and world stocks would not be sufficient to meet a surge in demand due to a BW release. This vaccine is not useful in preventing disease if given immediately following exposure to the virus.

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© 2005 Neal Chamberlain. All rights reserved. 
Site Last Revised 5/5/05
Neal Chamberlain, PhD. A. T. Still University of Health Sciences/Kirksville College of Osteopathic Medicine.

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