recent efforts to help will be sufficient.
http://www.economist.com/news/international/21625813-ebola-epidemic-west-africa-poses-catastrophic-threat-region-and-could-yet
There are two reasons for this. Those earlier outbreaks were often in isolated places where there are few opportunities for transmission far afield—the transfer of the virus between a wild animal and a human that sets off all such outbreaks is more likely off the beaten track. And they were mostly recognised quickly, with cases isolated and contacts traced from very early on; one was stopped this way in Congo in the past few months. The west African outbreak has broken through the barriers of isolation and into the general population, both in the countryside and the cities, and it was up and running before public-health personnel cottoned on. There is no reason to expect it to subside of its own accord, nor to expect it to come under control in the absence of a far larger effort to stop it.
Trying to be precise about how bad things could get, absent that effort, is not possible. This is not just because the actual number of cases is not well known. The rate at which cases give rise to subsequent cases, which epidemiologists call R?, is the key variable. For easily transmitted diseases R? can be high; for measles it is 18. For a disease like Ebola, much harder to catch, it is lower: estimates of R? in different parts of the outbreak range from 1.5 to 2.2. Any R? above 1 is bad news, though, and seemingly small differences in R? can matter a lot. An R? of 2.2 may sound not much bigger than an R? of 1.5, but it means numbers will double twice as fast.
And R? is not a constant. It depends both on the biology of the virus, the setting of its spread (city or country, slum or suburb) and the behaviour of the people among whom it is spreading. Over the course of the crisis the second two factors are bound to change as the virus moves to different places and as people start to adapt. Given high rates of mutation, which bring with them the possibility of evolutionary change, it is possible that the first could change, too. Peter Piot, one of the researchers who first identified the Ebola virus in 1976, stresses that the course of an outbreak does not always follow smooth curves; it can stutter and flare up. None of this complexity, though, offers much reassurance. While doubtless imperfect, plausible model-based extrapolations such as a recent one from America’s Centres for Disease Control and Prevention (CDC) suggest, in the absence of intervention, that there could be 1.4m cases in west Africa in the next three months.
Not that Ebola will necessarily be contained in west Africa. Despite it having infected health-care workers in America and Spain, and worries that one of those Americans could have passed it further, public-health experts are largely confident that outbreaks can be contained in countries with robust medical systems and the ability to trace contacts. But transfer to other places with poor health systems might allow the virus to take hold in new cities. Especially if it makes inroads into Nigeria, where one set of cases has been successfully controlled, the virus could travel on to India, rich in slums with poor health care, or China, where infection control in hospitals can be worryingly lax.
The steps to avert such a cataclysm are reasonably clear: cases must be identified quickly, patients isolated and their contacts traced; changes in behaviour which reduce transmission rates must be encouraged through education campaigns and community action. The difficulty is doing all these things quickly and on a large scale. Modelling suggests that getting 70% of the sick into settings that reduce transmission of the virus—clinics, treatment centres or safe settings for treatment in the community—would bring things under control. That is a tall order.
SNIP
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