While this group includes many different kinds of clinical symptoms and epidemiology, hemorrhagic fever viruses are generally characterized by profuse bleeding in the tissues. Viruses that cause hemorrhagic fever such as dengue, Rift Valley fever and yellow fever have been global health problems for centuries. Others are more exotic and can be even more deadly, including Ebola, Marburg (filoviruses), Lassa fever, among others, and have been investigated or even weaponized as biological warfare (BW) agents. Natural sources of infection are often through vectors such as biting insects, but aerosolized forms of transmission can also occur. For purposes of BW, hemorrhagic fevers that have been researched are in fact those that are easily grown in tissue culture and have demonstrated clinical infections by aerosols.
Hemorrhagic fevers can attack the lining of the vascular system, as well as infecting and destroying cells in vital organs. In general, these viruses cause febrile illness two to 21 days after exposure, often accompanied by rash, bleeding diathesis, and shock. In other words, symptoms and their presentation will vary depending on the disease syndrome in question, but begin with varying degrees of fever (mild to acute), then can develop leaking of fluid in the capillaries. Lassa fever, for example, begins with headache, sore throat, and a fever that becomes progressively severe. Spotted skin lesions (petechiae) develop from without, while bleeding may occur within the gastrointestinal tract. Case fatality is 2-4 percent, with 25 percent of infected individuals suffering deafness. Another hemorrhagic fever, Ebola, has a fatality rate approaching 90 percent, and follows a typical viral course in terms of symptomology. However, the disease becomes especially severe, with headache, vomiting, diarrhea, and severe hemorrhaging. According to Ken Alibek, the Margburg fever virus, a close relative to Ebola, was weaponized by the former Soviet Union.
An effective vaccine has been devised for yellow fever. However, few treatment options are available for some of the more severe hemorrhagic fevers such as Ebola and Lassa fever. Treatment with antiviral drugs such as ribavirin may be helpful if administered early in the course of illness. At present, natural transmission of hemorrhagic fevers can be reduced by mosquito abatement and other public health efforts, such as rodent control and special hygiene measures. |
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