Classification
The genera Ebolavirus and Marburgvirus were originally classified as the species of the now-obsolete Filovirus genus. In March, 1998, the Vertebrate Virus Subcommittee proposed in the International Committee on Taxonomy of Viruses (ICTV) to change the Filovirus genus to the Filoviridae family with two specific genera: Ebola-like viruses and Marburg-like viruses. This proposal was implemented in Washington, D.C., as of April, 2001 and in Paris as of July, 2002. In 2000, another proposal was made in Washington, D.C., to change the "-like viruses" to "-virus" resulting in today's Ebolavirus and Marburgvirus.[6]
The five characterised Ebola species are:
- Zaire ebolavirus (ZEBOV)
- Also known simply as the Zaire virus, ZEBOV has the highest case-fatality rate, up to 90% in some epidemics, with an average case fatality rate of approximately 83% over 27 years. There have been more outbreaks of Zaire ebolavirus than of any other species. The first outbreak took place on 26 August, 1976 in Yambuku.[7] Mabalo Lokela, a 44‑year-old schoolteacher, became the first recorded case. The symptoms resembled malaria, and subsequent patients received quinine. Transmission has been attributed to reuse of unsterilized needles and close personal contact.
- Sudan ebolavirus (SEBOV)
- Like the Zaire virus, SEBOV emerged in 1976; it was at first assumed to be identical with the Zaire species.[8] SEBOV is believed to have broken out first amongst cotton factory workers in Nzara, Sudan, with the first case reported as a worker exposed to a potential natural reservoir. Scientists tested local animals and insects in response to this; however, none tested positive for the virus. The carrier is still unknown. The lack of barrier nursing (or "bedside isolation") facilitated the spread of the disease. The most recent outbreak occurred in May, 2004. Twenty confirmed cases were reported in Yambio County, Sudan, with five deaths resulting. The average fatality rates for SEBOV were 54% in 1976, 68% in 1979, and 53% in 2000 and 2001.
- Reston ebolavirus (REBOV)
- This virus was discovered during an outbreak of simian hemorrhagic fever virus (SHFV) in crab-eating macaques from Hazleton Laboratories (now Covance) in 1989. Since the initial outbreak in Reston, Virginia, it has since been found in nonhuman primates in Pennsylvania, Texas and Siena, Italy. In each case, the affected animals had been imported from a facility in the Philippines,[9] where the virus has also infected pigs.[10] Despite its status as a Level‑4 organism and its apparent pathogenicity in monkeys, REBOV did not cause disease in exposed human laboratory workers.[11]
- Côte d'Ivoire ebolavirus (CIEBOV)
- Also referred to as Tai ebolavirus and by the English place name, "Ivory Coast", it was first discovered among chimpanzees from the Tai Forest in Côte d'Ivoire, Africa, in 1994. Necropsies showed blood within the heart to be brown; no obvious marks were seen on the organs; and one necropsy displayed lungs filled with blood. Studies of tissues taken from the chimpanzees showed results similar to human cases during the 1976 Ebola outbreaks in Zaire and Sudan. As more dead chimpanzees were discovered, many tested positive for Ebola using molecular techniques. The source of the virus was believed to be the meat of infected western red colobus monkeys, upon which the chimpanzees preyed. One of the scientists performing the necropsies on the infected chimpanzees contracted Ebola. She developed symptoms similar to those of dengue fever approximately a week after the necropsy, and was transported to Switzerland for treatment. She was discharged from hospital after two weeks and had fully recovered six weeks after the infection.[12]
- Bundibugyo ebolavirus
- On November 24, 2007, the Uganda Ministry of Health confirmed an outbreak of Ebola in the Bundibugyo District. After confirmation of samples tested by the United States National Reference Laboratories and the CDC, the World Health Organization confirmed the presence of the new species. On 20 February, 2008, the Uganda Ministry officially announced the end of the epidemic in Bundibugyo, with the last infected person discharged on 8 January, 2008.[13] An epidemiological study conducted by WHO and Uganda Ministry of Health scientists determined there were 116 confirmed and probable cases the new Ebola species, and that the outbreak had a mortality rate of 34% (39 deaths).[14]