Ebola: when a nightmare becomes reality.

BACKGROUND INFORMATION Ebola virus disease (EVD) was firstly identified in the Democratic Republic of Congo (DRC) and in Sudan in 1976, about nine years after the identification of the hemorrhagic fever due to the Marburg virus, another member of the Filoviridae family. Since most patients affected by Ebola do not develop frank hemorrhages, the formerly known term “Ebola hemorrhagic fever” has been replaced by “EVD”, to raise clinical suspicion and facilitate early recognition of the disease in absence of hemorrhagic symptoms. The ebolavirus genus includes five different species: Zaire, Sudan, Taϊ Forest , Bundibugyo, and Reston [1]. During less than four decades, between 1976 and 2012, 24 Ebola outbreaks have occurred in several Central African countries: DRC, Sudan, Gabon, the Republic of Congo (RC), and Uganda. Interestingly, the number of cases and outbreaks of EVD increased since the year 2000. Registered outbreaks, involving from a minimum of one up to a maximum of 425 individuals, were mainly caused by two different Ebola species: Zaire ebolavirus and Sudan ebolavirus. Such Ebola outbreaks are devastating in terms of high casefatality rates (ranging from 25% to 51% for Bundibugyo ebolavirus, from 41% to 71% for Sudan ebolavirus, from 44% to 90% for Zaire ebolavirus), but they are usually controlled by applying public health measures consisting in early isolation of patients, contact tracing and quarantine of exposed people and/or entire villages (cordon sanitaire). A lower case-fatality rate was observed in one outbreak which occurred in Uganda and was caused by the so-called Bundybugio strain. Another Ebola species, Reston ebolavirus, causing viral disease among simians and pigs in Asia, may infect also humans but without causing disease. Finally, before the current outbreak, only one case of Ebola due to a different virus species (Taϊ Forest ebolavirus), was reported in Western Africa, in a researcher dissecting an affected ape in Ivory coast [2]. Traditionally, Ebola outbreaks origin from a single case (i.e., a man going into the forest to hunter wild animals), which is followed by nosocomial amplification. Although fruit bats of the Pteropodidae family are assumed to represent the natural reservoir of the infection, other animal species living in the tropical rainforest, such as non-human primates (gorillas and chimpanzees) and antelopes, may acquire and introduce the infection into human populations through close contact with blood, secretions, organs or bodily fluids [3]. Then Ebola may spread through human-to-human transmission via direct contact with the body and/or bodily fluids of infected deceased persons, especially in the health care setting or in the household, or during traditional burial ceremonies. In such cases, the virus is supposed to enter human body through broken skin or mucous membranes. Infected persons develop EVD symptoms after an incubation period of about 4-11 days (range: 2 to 21 days) [1, 2, 4].