Chapter 197

Definition

Both Marburg virus and Ebola virus cause an acute febrile illness associated with a high mortality rate. This illness is characterized by multisystem involvement that begins with the abrupt onset of headache, myalgias, and fever and proceeds to prostration, rash, and shock and often to bleeding manifestations. Epidemics usually begin with a single case acquired from an unknown reservoir in nature (bats are suspected; see “Epidemiology,” below) and spread mainly through close contact with sick persons or their body fluids, either at home or in the hospital.

Etiology

The family Filoviridae (Fig. 197-1) comprises two antigenically and genetically distinct genera: Marburgvirus and Ebolavirus. Ebolavirus has five readily distinguishable species named for their original sites of recognition: Zaire, Sudan, Côte d′Ivoire, Bundibugyo, and Reston. Except for the Reston virus, all the Filoviridae are African viruses that cause severe and often fatal disease in humans (Figs. 197-2 and 197-3). The Reston virus, which has been exported from the Philippines on several occasions, has caused fatal infections in monkeys but only subclinical infections in humans. Different strains of the five Ebola species, isolated over time and space, exhibit remarkable sequence conservation, indicating marked genetic stability in their selective niche.

Figure 197-1

Phylogenetic tree of filoviruses. Marburgvirus and Ebolavirus are seen to be two different genera. The genus Ebolavirus includes five distinct species. Note that the Yambuku and Kikwit Zaire viruses are virtually identical even though the epidemics for which they were responsible are separated by two decades and hundreds of kilometers. Virtually every virus sequenced from each of those two epidemics is identical over the part of the genome examined. This pattern is typical of that seen with single introductions followed by human-to-human passage via needle or close contact in an African hospital. In the Marburgvirus branch of the tree, there is one major clade with a slightly divergent group characterized by the Ravn 1987 Kenya isolate. All the viruses from the major Angola 2005 outbreak are represented by a single virus because the sequences in this human-to-human epidemic are virtually identical. However, in the outbreak occurring in the Democratic Republic of the Congo (DRC) in 1999 and resulting from multiple independent infections after cave entry, two viruses with slightly different phylogenies are represented within the major group, and there is even another virus within the Ravn subgroup. These sequences were selected from hundreds determined at the U.S. Centers for Disease Control and Prevention and elsewhere. (Adapted from Peters, 2010.)

Figure 197-2

Left: Geographic sites of Ebolavirus species identification, as represented by dots (yellow, Zaire; green, Sudan; red, Côte d'Ivoire; black, Bundibugyo), in or adjacent to the Central African primary or secondary forest. Even Ebolavirus Côte d'Ivoire was isolated in the ...

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