Ebolavirus

The genus Ebolavirus (/iˈboʊlə/- or /əˈboʊləˌvaɪrəs/; ee-BOH-lə- or ə-BOH-lə-VY-rəs) is a virological taxon included in the family Filoviridae (filament-shaped viruses), order Mononegavirales. The members of this genus are called ebolaviruses, and encode their genome in the form of single-stranded negative-sense RNA. The six known virus species are named for the region where each was originally identified: Bundibugyo ebolavirus, Reston ebolavirus, Sudan ebolavirus, Taï Forest ebolavirus (originally Côte d'Ivoire ebolavirus), Zaire ebolavirus, and Bombali ebolavirus. The last is the most recent species to be named and was isolated from Angolan free-tailed bats in Sierra Leone. Each species of the genus Ebolavirus has one member virus, and four of these cause Ebola virus disease (EVD) in humans, a type of hemorrhagic fever having a very high case fatality rate. The Reston virus has caused EVD in other primates. Zaire ebolavirus has the highest mortality rate of the ebolaviruses and is responsible for the largest number of outbreaks of the six known species of the genus, including the 1976 Zaire outbreak and the outbreak with the most deaths (2014).

Ebolaviruses were first described after outbreaks of EVD in southern Sudan in June 1976 and in Zaire in August 1976. The name Ebolavirus is derived from the Ebola River in Zaire (now the Democratic Republic of the Congo), near the location of the 1976 outbreak, and the taxonomic suffix -virus (denoting a viral genus). This genus was introduced in 1998 as the "Ebola-like viruses". In 2002, the name was changed to Ebolavirus and in 2010, the genus was emended. Ebolaviruses are closely related to marburgviruses.

Ebolavirus is a filamentous, enveloped virus within the order Mononegavirales which also contains rabies and measles viruses. This order is characterized by non-segmented, single-stranded negative-sense RNA (-ssRNA) genomes that are surrounded by a helical nucleocapsid. Filoviruses encode seven different proteins that include: NP (nucleoprotein), VP35 (part of the polymerase complex), VP40 (matrix protein), GP (glycoprotein spike), VP30 (transcription activator), VP24 (second matrix protein), and L (RdRp). Of these proteins, GP and NP proteins are crucial for viral entry and replication.

GP is the protein responsible for pathogenic differences among ebolaviruses. GP encodes two glycoproteins, one of which is sGP (soluble glycoprotein) which has a role in Ebola pathogenesis. Research has suggested that sGP is able to subvert the host immune response increasing the EBOV pathogenesis.

NP contains both the filoviral genome and the antigenome. NP oligomerization is responsible for the NC (helical nucleocapsid) formation which allows the -ssRNA genome to be protected against host cell degradation by endonucleases and host immune response. NP is also shown to recruit host cell proteins to facilitate virus transcription and replication within the cytoplasm.

Ebolaviruses vary in size across variants, exhibiting cylindrical cores that are between 50 - 80 nm in diameter and lengths between 10 - 14 μm. Ebolavirus spikes extend out 10 nm and are spaced about 10 nm apart.

Researchers have found evidence of Ebola infection in three species of fruit bat. The bats show no symptoms of the disease, indicating that they may be the main natural reservoirs of the Ebolavirus. It is possible that there are other reservoirs and vectors. Understanding where the virus incubates between outbreaks and how it is transmitted between species will help protect humans and other primates from the virus.

The researchers found that bats of three species – Franquet's epauletted fruit bat (Epomops franqueti), the hammer-headed bat (Hypsignathus monstrosus) and the little collared fruit bat (Myonycteris torquata) – had either genetic material from the Ebola virus, known as RNA sequences, or evidence of an immune response to the disease. The bats showed no symptoms themselves.