Viral hemorrhagic fevers (VHFs)
Basic Facts
Viral hemorrhagic fevers are a class of diseases, contracted from viruses, that include:
- Ebola
- Marburg virus
- Other illnesses (e.g., Lassa, Machupo)
The following are general characteristics of VHFs:
- They are naturally occurring in mosquitoes, ticks, rodents, and other animals.
- They cause massive internal and external bleeding.
- The fatality rate can be as high as 90 percent.
- With the exception of yellow fever and Argentine hemorrhagic fever, for which vaccines have been developed, no vaccines exist that can protect against these diseases.
- No drugs are available to combat the viruses that cause VHFs.
VHFs as a Weapon
- In aerosol form, any of these viruses could be highly lethal.
- Soviet scientists are known to have weaponized the Marburg virus, a close cousin of Ebola.
- Many other VHFs have potential for aerosol dissemination or weaponization.
Identifying an Attack
- Evidence of an attack would most likely come when patients fall ill.
- Because natural outbreaks of VHFs have been known to occur, investigators would have to rule out nonterrorist causes.
VHF Illnesses
Ebola
Of all the VHFs, Ebola is probably the best known because of outbreaks in Africa.
Exposure:
- Ebola can be passed to humans through infected animals.
- Once a person becomes ill, the virus can be transmitted to others through exposure to blood or bodily fluids, including airborne droplets from coughing.
- Outbreaks most often occur in areas where isolation of patients is difficult.
Symptoms:
- Patients usually become sick four to six days after exposure.
- The disease attacks blood vessels and organs, particularly the liver, spleen, and kidneys, causing heavy bleeding.
- Symptoms include fever, vomiting, diarrhea, and heavy bleeding from multiple sites.
Recovery/Mortality Rate:
- The fatality rates range from 50 to 90 percent.
- Death usually occurs within one to two weeks of falling ill, most often from shock and blood loss.
Diagnosis
- Specific laboratory tests do exist to detect the virus in a blood sample.
- The handling of the virus is a biohazard, so tests need to be performed in a biosafety level 4 laboratory.
- Diagnosis is usually made by monitoring symptoms and by tracking a patient's exposure to the virus.
Treatment
Physicians treat the patient with fluids to prevent dehydration and try to control bleeding.
Vaccine
- No vaccine currently exists for Ebola (or most other VHFs).
- Research continues on a possible vaccine and antiviral drug treatments; more information on clinical trials is available at NIAID's website, www3.niaid.nih.gov/biodefense.
- Even under lab conditions, the virus is contagious, complicating vaccine research.
Prevention
Because of the contagious nature of Ebola, quick identification and isolation of victims are essential to containing the spread of it and other VHF diseases. While considered highly contagious, Ebola is spread only by direct contact with patients and their bodily fluids.
- Avoid infected animals or people.
- Isolate and monitor patients and people who have had close physical contact with patients.
- Hospital workers and caregivers must wear gowns, gloves, and masks and practice extreme caution while treating patients.
- Promptly bury or cremate patients who die from the disease because a corpse can be infectious for a period of time after death.
What We Don't Know About Ebola Prevention
- It is not known how long a person can remain contagious after recovering.
- Some research suggests that those patients who survive can continue to pass the disease to others through sexual contact for up to seven weeks.
Assessing the Risk
- The ingredients to weaponize VHFs are moderately available, since naturally occurring outbreaks of Ebola could become a source for a terrorist organization. Some less virulent VHF viruses can be obtained from animals.
- VHFs are generally minimally stable, and few can be produced in aerosol form for widespread release.
- Terrorists would have to be highly skilled to weaponize VHFs since they are extremely dangerous to work with, even in the lab.
- VHFs are highly lethal, especially because there are no known vaccines or treatments to protect against most of them.
More information on disasters and emergencies is available at the U.S. Department of Health and Human Service's website: http://www.hhs.gov/emergency
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