Causes
Main articles: Ebolavirus (taxonomic group) and Ebola virus (specific virus)
Life cycles of the Ebolavirus
EVD is caused by four of five viruses classified in the genus Ebolavirus, family Filoviridae, order Mononegavirales. The four disease-causing viruses are Bundibugyo virus (BDBV), Sudan virus (SUDV), Taï Forest virus (TAFV), and one called, simply, Ebola virus (EBOV, formerly Zaire Ebola virus)). Ebola virus is the sole member of the Zaire ebolavirus species and the most dangerous of the known Ebola disease-causing viruses, as well as being responsible for the largest number of outbreaks.[16] The fifth virus, Reston virus (RESTV), is not thought to be disease-causing in humans. These five viruses are closely related to the Marburg viruses.
Transmission
Human-to-human transmission can occur via direct contact with blood or bodily fluids from an infected person (including embalming of an infected dead person) or by contact with objects contaminated by the virus, particularly needles and syringes.[17] The potential for widespread EVD infections is considered low as the disease is only spread by direct contact with the secretions from someone who is showing signs of infection.[17] The symptoms limit a person's ability to spread the disease as they are often too sick to travel.[18] Because dead bodies are still infectious, local traditional burial rituals may spread the disease
.[19] Nearly two thirds of the cases of Ebola in Guinea during the 2014 outbreak are believed to be due to burial practices.[20] Semen may be infectious in survivors for up to 3 months.[21] It is not entirely clear how an outbreak is initially started.[22] The initial infection is believed to occur after ebola virus is transmitted to a human by contact with an infected animal's body fluids.
One of the primary reasons for spread is that the health systems in the part of Africa where the disease occurs function poorly.[23] Medical workers who do not wear appropriate protective clothing may contract the disease.[24] Hospital-acquired transmission has occurred in African countries due to the reuse of needles and lack of universal precautions.[25][26] Some healthcare centers caring for people with the disease do not have running water.[21]
Airborne transmission has not been documented during EVD outbreaks.[2] They are, however, infectious as breathable 0.8– to 1.2-μm laboratory-generated droplets.[27] The virus has been shown to travel, without contact, from pigs to primates, although the same study failed to demonstrate similar transmission between non-human primates.[28]
Bats drop partially eaten fruits and pulp, then land mammals such as gorillas and duikers feed on these fallen fruits. This chain of events forms a possible indirect means of transmission from the natural host to animal populations, which has led to research towards viral shedding in the saliva of bats. Fruit production, animal behavior, and other factors vary at different times and places that may trigger outbreaks among animal populations.[29]
http://en.wikipedia.org/wiki/Ebola_virus_disease
