Cholera is the rare disease that can kill within hours of infection. Whip-like swimming bacteria known as Vibrio cholerae attack the lining of the small intestine, emitting proteins which leech fluid from its cells. This causes severe diarrhoea and vomiting, which in turn lead to dehydration and electrolyte imbalance, then reduced blood pressure, shock and death.
Even so, cholera's mortality rate drops to around one percent if properly treated. The remedy is straightforward: patients drink measured doses of salted rice water, shifting the osmotic gradient in their gut and slowing the leak of chloride through the walls of their intestinal cells. Prevention is also simple. The disease spreads through faeces in drinking water. Proper latrines and disinfected water stop it in its tracks.
In Haiti, nearly 600 people had died in the present cholera outbreak by the time The Review went to press. The death rate appeared to be about 6.5 per cent. The fact that this disease is easy to prevent, easy to cure and yet rampant is another proof of the depths of misery into which Haiti has descended since January's earthquake. But Haiti is not the only - or even the principle - part of the world that is vulnerable to cholera. So far this year more than 40,000 cases have been recorded in Cameroon, Chad, Niger and Nigeria. Other diseases, slower to kill but just as easy to treat, account for many more deaths in Africa.
Like cholera, bilharzia is waterborne. Untreated, it can lead to bladder cancer and brain damage. A single dose of praziquantel, once a year, stops it. Each dose costs pennies, and yet the World Health Organization has estimated that 200,000 people in sub-Saharan Africa die each year as a result of the disease, a horrifying figure when one considers that bilharzia is rarely fatal. Similar stories can be told for sleeping sickness, elephantiasis and river blindness. On Sunday an article in Britain's The Observer asserted that Africa's big-name diseases - HIV, malaria and tuberculosis - distracted from efforts to provide cheap, effective cures for more than a billion sufferers of these less-publicised conditions.
It goes without saying that the world exists in a constant state of epidemiological emergency. But that only means a system of triage is required: limited resources have to be directed to the places where they can do the most good. This may mean ignoring big complicated problems to focus on many smaller, more easily resolved ones. But it will also mean attending to the question of which problems the world actually faces, and rejecting fatalism about some of its oldest blights.
It would be perverse to say that Haiti is fortunate: analysts predict its current epidemic will get much worse before it gets better. Yet the nation's recent catalogue of misfortunes has kept it in the news and at the top of the humanitarian agenda. However inadequate the humanitarian response ultimately turns out to be, it is at least reasonable to expect that cholera will be eliminated, as it has been throughout much of Asia (there was no outbreak in Pakistan after the floods, for instance). Such a hope is less realistic in the case of West Africa, and less realistic still in the case of the many chronic or only eventually fatal illnesses which nonetheless affect millions upon millions of people. They, alas, don't have the world's attention.
Disease is a depressing subject. Even compared to other causes of death, it is peculiarly unpleasant to think about. It offers nothing to fight, no one to hate, nothing sublime in its terribleness. And yet, almost uniquely among the causes of human suffering, thinking about disease pays off. We can understand it, grasp its patterns and mechanisms. We can see how it works and how to fight it. We can also choose our battles, if only as charitable donors and campaigners. We need to think about that, too. Haiti seems winnable. So do a few other places. Once we have thought, we need to act.