The taxonomy, ecology, and epidemiology of these viruses are summarized below. Transmission of VHFs varies with the specific virus. However, all of the VHFs, with the exception of dengue, are potentially transmitted via aerosol, underscoring their possible role as BW agents. Table 3-1 provides the taxonomy of VHFs. Viral hemorrhagic fever is a clinical syndrome featuring fever, myalgia, malaise, and hemorrhage, and in some cases, hypotension, shock, and death.
Viral pathogenesis is complex, incompletely understood, and varies among specific viruses.
Some infections result in immune complex deposition which activates complement and other inflammatory cascades. This process damages vascular endothelium, results in capillary leak, and deregulates vascular smooth muscle tone. These lead to hypotension, shock, and end-organ failures. Hemorrhage can also be enhanced by specific end-organ failures. For example, yellow fever can cause massive hepatic necrosis resulting in a deficiency of vitamin K-dependent clotting factors.