Viral hemorrhagic fevers 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 multisystem syndrome, meaning that multiple organ systems in the body are affected. The Centers for Disease Control and Prevention (CDC) has designated the group of viral hemorrhagic fevers as a Category A bioterrorism threat. According to a June 1999 multidisciplinary panel, Category A agents are considered to pose the greatest threat to US health and security.
Virus Categories and Diseases Viral hemorrhagic fevers are caused by a diverse group of ribonucleic acid (RNA) viruses in four separate families:
- Arenavirus - West Africa's Lassa fever, and Argentine, Bolivian, Brazilian, and Venezuelan hemorrhagic fevers
- Filovirus - Ebola and Marburg
- Bunyavirus - Hantavirus
- Flavivirus - Yellow fever and Dengue fever
Viral Hemorrhagic Fever as a Biological Weapon
The most publicized viral hemorrhagic fevers are the Ebola and Marburg viruses. They produce grotesque, lethal symptoms making them favorites with the popular media. Terrorist groups have attempted to weaponize various agents that cause viral hemorrhagic fever by aerosolizing infected body fluids or rodent excrement.
Virus Hosts and Vectors
Viruses associated with most cases of viral hemorrhagic fever are zoonotic. This means that these viruses naturally reside in an animal reservoir host or arthropod vector. The cotton rat, deer mouse, house mouse, and other field rodents are examples of reservoir hosts. Arthropod ticks and mosquitoes serve as vectors for some of the illnesses. However, the hosts of some viruses remain unknown -- Ebola and Marburg viruses are well-known examples.
Virus Transmission - Rodents and Arthropods
Viruses causing hemorrhagic fever are initially transmitted to humans when the activities of infected reservoir hosts or vectors and humans overlap. The viruses carried in the rodents are transmitted when humans have contact with urine, fecal matter, saliva, or other body excretions from infected rodents. The viruses associated with arthropod vectors are spread most often when the vector mosquito or tick bites a human, or when a human crushes a tick. However, some of these vectors may spread virus to animals, livestock, for example. Humans then become infected when they care for or slaughter the animals.
Virus Transmission - Humans
Some viruses that cause hemorrhagic fever can spread from one person to another, once an initial person has become infected. Ebola, Marburg, Lassa and Crimean-Congo hemorrhagic fever viruses are examples. This type of secondary transmission of the virus can occur directly, through close contact with infected people or their body fluids. It can also occur indirectly, through contact with objects contaminated with infected body fluids. For example, contaminated syringes and needles have played an important role in spreading infection in outbreaks of Ebola hemorrhagic fever and Lassa fever.
Symptoms of Viral Hemorrhagic Fever
Specific signs and symptoms vary by the type of viral hemorrhagic fever, but initial signs and symptoms often include high fever, fatigue, dizziness, muscle aches, loss of strength, and exhaustion. Patients with severe cases of viral hemorrhagic fever often show signs of bleeding under the skin, in internal organs, or from body orifices like the mouth, eyes, or ears. However, although they may bleed from many sites around the body, patients rarely die because of blood loss. Severely ill patient cases may also show shock, nervous system malfunction, coma, delirium, and seizures. Some types of viral hemorrhagic fever are associated with kidney failure.
Treatment of Viral Hemorrhagic Fever
Patients receive supportive therapy, but generally speaking, there is no other treatment or established cure for viral hemorrhagic fever. Ribavirin, an anti-viral drug, has been effective in treating some individuals with Lassa fever.
Information for this article was taken from:
- www.cdc.gov Viral Hemorrhagic Fevers
- Darling RG, et al - Threats in bioterrorism I: CDC category A agents - Emergency Medicine Clinics of North America; May 2002; vol 20(2).
- Miller JM - Agents of Bioterrorism: Preparing for Bioterrorism at the Community Health Care Level - Infectious Disease Clinics of North America; Dec 2001; vol 15(4).
