Zaire ebolavirus
Zaire ebolavirus, more commonly known as Ebola virus (/iˈboʊlə, ɪ-/; EBOV), is one of six known species within the genus Ebolavirus.[1] Four of the six known ebolaviruses, including EBOV, cause a severe and often fatal hemorrhagic fever in humans and other mammals, known as Ebola virus disease (EVD). Ebola virus has caused the majority of human deaths from EVD, and was the cause of the 2013–2016 epidemic in western Africa,[2] which resulted in at least 28,646 suspected cases and 11,323 confirmed deaths.[3][4]
This article is about the species Zaire ebolavirus. For the genus, see Ebolavirus. For the disease, see Ebola virus disease. For other uses, see Ebola (disambiguation).
Ebola virus and its genus were both originally named for Zaire (now the Democratic Republic of the Congo), the country where it was first described,[1] and was at first suspected to be a new "strain" of the closely related Marburg virus.[5][6] The virus was renamed "Ebola virus" in 2010 to avoid confusion. Ebola virus is the single member of the species Zaire ebolavirus, which is assigned to the genus Ebolavirus, family Filoviridae, order Mononegavirales. The members of the species are called Zaire ebolaviruses.[1][7] The natural reservoir of Ebola virus is believed to be bats, particularly fruit bats,[8] and it is primarily transmitted between humans and from animals to humans through body fluids.[9]
The EBOV genome is a single-stranded RNA, approximately 19,000 nucleotides long. It encodes seven structural proteins: nucleoprotein (NP), polymerase cofactor (VP35), (VP40), GP, transcription activator (VP30), VP24, and RNA-dependent RNA polymerase (L).[10]
Because of its high fatality rate (up to 83 to 90 percent),[11][12] EBOV is also listed as a select agent, World Health Organization Risk Group 4 Pathogen (requiring Biosafety Level 4-equivalent containment), a US National Institutes of Health/National Institute of Allergy and Infectious Diseases Category A Priority Pathogen, US CDC Centers for Disease Control and Prevention Category A Bioterrorism Agent, and a Biological Agent for Export Control by the Australia Group.
Ecology[edit]
Ebola virus is a zoonotic pathogen. Intermediary hosts have been reported to be "various species of fruit bats ... throughout central and sub-Saharan Africa". Evidence of infection in bats has been detected through molecular and serologic means. However, ebolaviruses have not been isolated in bats.[8][38] End hosts are humans and great apes, infected through bat contact or through other end hosts. Pigs in the Philippines have been reported to be infected with Reston virus, so other interim or amplifying hosts may exist.[38] Ebola virus outbreaks tend to occur when temperatures are lower and humidity is higher than usual for Africa.[39] Even after a person recovers from the acute phase of the disease, Ebola virus survives for months in certain organs such as the eyes and testes.[40]
A virus of the genus Ebolavirus is a member of the species Zaire ebolavirus if:[1]
Evolution[edit]
Zaire ebolavirus diverged from its ancestors between 1960 and 1976.[59] The genetic diversity of Ebolavirus remained constant before 1900.[59][60] Then, around the 1960s, most likely due to climate change or human activities, the genetic diversity of the virus dropped rapidly and most lineages became extinct.[60] As the number of susceptible hosts declines, so does the effective population size and its genetic diversity. This genetic bottleneck effect has implications for the species' ability to cause Ebola virus disease in human hosts.
A recombination event between Zaire ebolavirus lineages likely took place between 1996 and 2001 in wild apes giving rise to recombinant progeny viruses.[61] These recombinant viruses appear to have been responsible for a series of outbreaks among humans in Central Africa in 2001–2003.[61]
Zaire ebolavirus – Makona variant caused the 2014 West Africa outbreak.[62] The outbreak was characterized by the longest instance of human-to-human transmission of the viral species.[62] Pressures to adapt to the human host were seen at this time, however, no phenotypic changes in the virus (such as increased transmission, increased immune evasion by the virus) were seen.