INTRODUCTION

The term viral hemorrhagic fever (VHF) refers to an acute systemic illness classically involving fever, a constellation of initially nonspecific signs and symptoms, and a propensity for bleeding and shock. VHFs are caused by small, single-stranded, lipid-enveloped RNA viruses from four families (Table 192.1). Although VHFs collectively exist worldwide, the distribution of any given virus is generally restricted by the distribution of its natural reservoir and/or arthropod vector. Depending on the specific disease, virus may be transmitted to humans through direct exposure to contaminated blood or excreta of the animal reservoir or through the bite of an arthropod. Secondary human-to-human transmission also occurs with Ebola, Marburg, Crimean Congo hemorrhagic fever (CCHF), and the arenaviruses, especially Lassa (Table 192.1).

PATHOLOGY AND PATHOGENESIS

Consideration of the underlying pathogenesis helps guide treatment. Although the pathophysiology of the VHFs varies with the specific virus, certain common hallmarks can be identified, namely microvascular instability and impaired hemostasis. Contrary to popular thought, mortality in VHF usually results not directly from exsanguination, but rather from a process akin to septic shock, with insufficient effective circulating intravascular volume leading to cellular dysfunction and multiorgan system failure. In fact, external bleeding is seen in a minority of cases.