13 Ebola virus: where does it come from and where is it going?

This chapter discusses the emergence and natural history of Ebola viruses. The fact that the Ebola virus subtypes, which have caused human disease episodes, have been different from one another makes it clear that a common source human-to-human transmission chain extending across sub-Saharan Africa is not the case and rather, virus subtypes lodged at or near each site of the recent human disease episodes have been responsible. Filovirus virions are enveloped and pleomorphic, appearing filamentous or bacilliform, U-shaped, 6-shaped, or circular. Particles have a uniform diameter of 80 nm, but vary greatly in length. The degree of the stability of filovirus sequences overall and the absence of genetic variability among Ebola virus isolates obtained within an outbreak match the character of other member viruses of the order, Mononegavirales. In rhesus monkeys, cynomolgus monkeys, African green monkeys, and baboons inoculated with Marburg virus or the Zaire subtype of Ebola virus, the incubation period is 4–6 days, during which time virus replicates to high titer in the reticuloendothelial system, endothelium, liver, and lungs. It is found that with the onset of clinical disease, there is severe necrosis of these target organs, which is most evident in the liver and there is an interstitial hemorrhage, which is most evident in the gastrointestinal tract.