Much worse to come
The Ebola epidemic in west Africa poses a catastrophic threat to the region, and could yet spread further
ON MARCH 25th the World Health Organisation (WHO) reported a rash of cases of Ebola in Guinea, the first such ever seen in west Africa. As of then there had been 86 suspected cases, and there were reports of suspected cases in the neighbouring countries of Sierra Leone and Liberia as well. The death toll was 60.
On October 15th the WHO released its latest update. The outbreak has now seen 8,997 confirmed, probable and suspected cases of Ebola. All but 24 of those have been in Guinea (16% of the total), Sierra Leone (36%) and Liberia (47%). The current death toll is 4,493. These numbers are underestimates; many cases, in some places probably most, go unreported.
This all pales, though, compared with what is to come. The WHO fears it could see between 5,000 and 10,000 new cases reported a week by the beginning of December; that is, as many cases each week as have been seen in the entire outbreak up to this point. This is the terrifying thing about exponential growth as applied to disease: what is happening now, and what happens next, is always as bad as the sum of everything that has happened to date.
Exponential growth cannot continue indefinitely; there are always barriers. In the previous 20 major outbreaks of the disease since its discovery in 1976, all of which took place in and around the Democratic Republic of the Congo, the initial rapid spread quickly subsided. In the current outbreak, though, the limits have been pushed much further back; it has already claimed more victims than all the previous outbreaks put together.
Grim reckoning
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 Rο, is the key variable. For easily transmitted diseases Rο can be high; for measles it is 18. For a disease like Ebola, much harder to catch, it is lower: estimates of Rο in different parts of the outbreak range from 1.5 to 2.2. Any Rο above 1 is bad news, though, and seemingly small differences in Rο can matter a lot. An Rο of 2.2 may sound not much bigger than an Rο of 1.5, but it means numbers will double twice as fast.
And Rο 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.
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Veni, vidi, vaccini
Changing behaviour could slow the spread of the virus; a vaccine could potentially stop it. In large part because of worries that Ebola might be used as a biological weapon, vaccines that protect lab animals against the virus were already on the shelf when the outbreak began. Two are now being tested for safety in humans, and one of them could, if it is safe, be tested for efficacy quite soon, most likely in health-care workers in west Africa. Its maker, GlaxoSmithKline, could have 10,000 doses ready in a few months. Meanwhile thought is going into how to scale up production of any vaccine that proves successful. The ideal would be to come up with some mixture of direct payment to companies and guaranteed purchases that would mean copious stocks were available the moment the good news came through.
The other vaccine in trials might possibly, on the basis of animal tests, have the added benefit of helping those infected fight the virus as well as keeping the uninfected safe. At the moment there is a striking lack of such therapies: ZMapp, a cocktail of antibodies that has worked in animals, is of unproven efficacy and exhausted supply. A lower-tech alternative is to use blood serum from recovered patients, which contains the antibodies that helped them fight the virus. Such blood would have to be screened for other pathogens and matched to the recipients’ blood type, but WHO experts have been guardedly optimistic about the idea.
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http://www.economist.com/news/intern...-and-could-yet
Originally Posted by MelissaWV
Bravo. It's paranoia that ebola has been contracted in this nation, and that I don't trust people to self-quarantine and the CDC to provide straight answers to everyone, but on the other hand I should be discussing other topics that involve the Government being shady and incompetent. The logic is so beautiful and flawless, really.
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