ABSTRACT

Historically, the term viral hemorrhagic fever (VHF) refers to a clinical illness or syndrome characterized by high fever and a bleeding diathesis caused by a virus in one of four virus families [1]. The four virus families that cause VHFs are

Arenaviridae

,

Bunyaviridae

,

Flaviviridae

, and

Filoviridae

. At present, 12 specific viruses cause VHFs, but the number is likely to expand as new viruses emerge. Although all of the VHFs are caused by small RNA viruses with lipid envelopes [1], the viruses are biologically, geographically, and ecologically diverse. Most of the VHFs are zoonoses (transmissible from animal to man). The ecology and host reservoir of the viruses that cause VHFs, except for the

Filoviridae

, are well-defined. Transmission to man may occur from contact with the infected reservoir, a bite from an infected arthropod, aerosols generated from infected rodent excreta, or direct contact with

infected patients or animal carcasses [2]. With the exception of the flaviviruses and Rift Valley Fever Virus (RVF), which are not considered transmissible from person to person, infected humans can spread VHF infection to close contacts [1,2]. The ecology and host reservoir for the

Filoviridae

are still unknown. The signs, symptoms, clinical course, mortality, and pathogenesis of the hem-

orrhagic fever viruses vary among the virus families, the viruses within a specific virus family, and the virus species or strains of a particular virus. Hemorrhage may not necessarily occur in each individual case of VHF and, if seen, may be a late event in the course of the disease. However, hemorrhage and circulatory shock are seen as clinical manifestations among the patients in most VHF outbreaks. Other symptoms such as fever, headache, generalized myalgia, prostration conjunctivitis, rash, lymphadenopathy, pharyngitis, and edema are common to most VHF outbreaks.