Here is some basic background information on this outbreak of Ebola, so as to limit repetition in future posts.
This outbreak began in late December 2013 when a two year old boy in Guinea began suffering from a “mystery” illness. The location of this first case, in the village of Meliandou, is very close to the borders of Sierra Leone and Liberia. While cholera and malaria are both very common in this area, Ebola has not previously been seen in west Africa so it was not suspected for some time. By the time it was confirmed in late March 2014 that the disease was Ebola, it had already spread.
This strain is the Zaire strain, the first type of Ebola identified in 1976 in what is now the Democratic Republic of the Congo (then Zaire). The Zaire strain is the most deadly of several strains with some outbreaks killing 90% of those who became ill. The current outbreak has a fatality rate of around 70%. Some fatality rates have been calculated by dividing the number of deaths by the number of cases, but this is inaccurate as it does not account for those who are infected but whose case has yet to resolve (either in death or recovery). As the number of cases is doubling every 3 weeks or so it is important to look at only resolved cases in estimating the fatality rate as there are very many cases that have no resolution as of yet.
The incubation period for Ebola is 2-21 days, with a week or so being the most common. Ebola is not contagious in this incubation period. After the incubation, symptoms begin to show and the infected person is then contagious. Initially the symptoms are non-specific, typically a fever and sweating, followed by vomiting and diarrhea. The amount of virus released from the infected individual – and thus the chance for contagion – increases with the progression of the disease and the severity of the symptoms. While bleeding from pores, eyes, and ears are some of the more dramatic signs of Ebola, they develop late in the disease if at all.
Ebola is spread through contact with bodily fluids – sweat, saliva, blood, feces, etc. It can be spread without direct physical contact with an infected individual as droplets of saliva (or any other bodily fluids) that are coughed or sneezed can carry the virus through the air to the eyes, mouth, or nose of other individuals. This does not, however, make the virus “airborne” in the technical sense as it cannot travel very far as it is quickly settled out of the air, unlike viruses like the flu which can linger in the air for a long time. Coming into contact with an infected individual’s sweat (or other bodily fluids) on a seat, glass, or other surface can infect a person if it reaches a point of entry, like eating before washing hands or rubbing your eye. NPR reports that “[a] drop of blood can remain contagious outside the body. And virus particles can survive for days or weeks, depending on the environment. Ultraviolet light, heat and exposure to oxygen gradually deactivate the virus, while cooler temperatures and humidity help keep it active.”
It is thought that fruit bats may be the native carriers of Ebola. While non-human primates can also contract Ebola it tends to kill them rather rapidly, making them inappropriate carriers long-term. They are likely infected from the same carrier animals that transmit the virus to humans.
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