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.

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