Ebola Virus Disease - Epidemiology

Epidemiology

Distribution of Ebola and Marburg virus in Africa (note that integrated genes from filoviruses have been detected in mammals from the New World as well). (A) Known points of filovirus disease. Projected distribution of ecological niche of: (B) all filoviruses, (C) ebolaviruses, (D) marburgviruses. For more about specific outbreaks and their descriptions, see List of Ebola outbreaks.

Outbreaks of EVD have mainly been restricted to Africa. The virus often consumes the population. Governments and individuals quickly respond to quarantine the area while the lack of roads and transportation helps to contain the outbreak. EVD was first described after almost simultaneous viral hemorrhagic fever outbreaks occurred in Zaire and Sudan in 1976. EVD is believed to occur after an ebolavirus is transmitted to a human index case via contact with an infected animal host. Human-to-human transmission occurs via direct contact with blood or bodily fluids from an infected person (including embalming of a deceased victim) or by contact with contaminated medical equipment such as needles. In the past, explosive nosocomial transmission has occurred in underequipped African hospitals due to the reuse of needles and/or absence of proper barrier nursing. Aerosol transmission has not been observed during natural EVD outbreaks. The potential for widespread EVD epidemics is considered low due to the high case-fatality rate, the rapidity of demise of patients, and the often remote areas where infections occur.

Ebola virus disease (EVD) outbreaks

Year	Virus	Geographic location	Human cases/deaths (case-fatality rate)
1976	SEBOV	Juba, Maridi, Nzara, and Tembura, Sudan	284/151 (53%)
1976	EBOV	Yambuku, Zaire	318/280 (88%)
1977	EBOV	Bonduni, Zaire	1/1 (100%)
1979	SUDV	Nzara, Sudan	34/22 (65%)
1988	EBOV	Porton Down, United Kingdom	1/0 (0%)
1994	TAFV	Taï National Park, Côte d'Ivoire	1/0 (0%)
1994–1995	EBOV	Woleu-Ntem and Ogooué-Ivindo Provinces, Gabon	52/32 (62%)
1995	EBOV	Kikwit, Zaire	317/245 (77%)
1996	EBOV	Mayibout 2, Gabon	31/21 (68%)
1996	EBOV	Sergiyev Posad, Russia	1/1 (100%)
1996–1997	EBOV	Ogooué-Ivindo Province, Gabon; Cuvette-Ouest Department, Republic of the Congo	62/46 (74%)
2000–2001	SUDV	Gulu, Mbarara, and Masindi Districts, Uganda	425/224 (53%)
2001–2002	EBOV	Ogooué-Ivindo Province, Gabon; Cuvette-Ouest Department, Republic of the Congo	124/97 (78%)
2002	EBOV	Ogooué-Ivindo Province, Gabon; Cuvette-Ouest Department, Republic of the Congo	11/10 (91%)
2002–2003	EBOV	Cuvette-Ouest Department, Republic of the Congo; Ogooué-Ivindo Province, Gabon	143/128 (90%)
2003–2004	EBOV	Cuvette-Ouest Department, Republic of the Congo	35/29 (83%)
2004	EBOV	Koltsovo, Russia	1/1 (100%)
2004	SUDV	Yambio County, Sudan	17/7 (41%)
2005	EBOV	Cuvette-Ouest Department, Republic of the Congo	11/9 (82%)
2007	EBOV	Kasai Occidental Province, Democratic Republic of the Congo	264/186 (71%)
2007–2008	BDBV	Bundibugyo District, Uganda	116/39 (34%)
2008–2009	EBOV	Kasai Occidental Province, Democratic Republic of the Congo	32/15 (47%)
2011	SUDV	Luweero District, Uganda	1/1 (100%)
2012	SUDV	Kibaale District, Western Uganda	24/17 (71%)
2012	BDBV	Orientale Province, Democratic Republic of the Congo	72/32 (44%)

While investigating an outbreak of Simian hemorrhagic fever virus (SHFV) in November 1989, an electron microscopist from USAMRIID discovered filoviruses similar in appearance to Ebola in tissue samples taken from Crab-eating Macaque imported from the Philippines to Hazleton Laboratories Reston, Virginia. Due to the lethality of the suspected and previously obscure virus, the investigation quickly attracted attention. Blood samples were taken from 178 animal handlers during the incident. Of those, six animal handlers eventually seroconverted. When the handlers failed to become ill, the CDC concluded that the virus had a very low pathogenicity to humans.

The Philippines and the United States had no previous cases of infection, and upon further isolation it was concluded to be another strain of Ebola or a new filovirus of Asian origin, and named Reston ebolavirus (REBOV) after the location of the incident.

Because of the virus's high mortality, it is a potential agent for biological warfare. In 1992, members of Japan's Aum Shinrikyo cult considered using Ebola as a terror weapon. Their leader, Shoko Asahara, led about 40 members to Zaire under the guise of offering medical aid to Ebola victims in a presumed attempt to acquire a virus sample.

Given the lethal nature of Ebola, and since no approved vaccine or treatment is available, it is classified as a biosafety level 4 agent, as well as a Category A bioterrorism agent by the Centers for Disease Control and Prevention. It has the potential to be weaponized for use in biological warfare. The effectiveness as a biological weapon is compromised by its rapid lethality as patients quickly die off before they are capable of effectively spreading the contagion. The attention gathered from the outbreak in Reston prompted an increase in public interest, leading to the publication of numerous fictional works and a non-fiction work authored by Richard Preston known as The Hot Zone.

The BBC reports in a study that frequent outbreaks of Ebola may have resulted in the deaths of 5,000 gorillas.