ABSTRACT
Hemorrhagic diathesis is the consequence of a number of viral and rickettsial diseases. This chapter presents the catalogue of lesions observed for each entity in search for particular patterns of hemorrhagic involvement and clinical and experimental data regarding the pathogenic mechanisms of bleeding diathesis for each infection. Among the hundreds of togaviruses that have been isolated, only a few have been considered to cause hemorrhagic fevers. Etiologic agents are dengue viruses 1 to 4, yellow fever virus, Kyasanur Forest disease virus, Omsk hemorrhagic fever virus, and Chikungunya virus. Experimental yellow fever viral infection of nonhuman primates has added to our understanding of yellow fever pathogenesis. Dengue hemorrhagic fever is but one of several clinical manifestations of dengue virus infection. Two arthropod-borne bunyavirus diseases qualify as hemorrhagic fevers, Rift Valley fever and Congo-Crimean hemorrhagic fever. Rift Valley fever virus is transmitted to sheep by mosquitoes in African enzootics.
