Many infections kill slowly. Hardly any are lethal within 24 hours of the onset of symptoms. Bubonic plague takes days to kill and haemorrhagic smallpox takes a week. Cholera and inhalation anthrax are about the only diseases whose victims can wake up feeling fit but be dead by nightfall.
The cholera bacterium produces a toxin that sticks to the cells lining the small intestine, enters them and starts a chain of events leading to the leak of chloride through cell membrane channels. This causes massive diarrhoea, then blood pressure collapse, shock and death. Treatment is straightforward: oral replacement therapy (ORT) with salty rice water. Glucose from the rice creates an osmotic force that drives fluid back into the cells. In severe cases a drip is needed to start the process. A cholera cot – a camp bed with a hole and a bucket – is used to measure the diarrhoea and quantitatively guide the ORT. Antibiotics help by shortening the illness.
ORT should reduce the mortality rate from 50 per cent in the vulnerable to about 1 per cent. The figure of around 8 per cent reported from Haiti in the last few days is probably explained in part by inexperience. Haiti escaped completely during the massive cholera outbreaks in the Americas in the 1990s. They started without warning in 1991 (no cases were recorded in 1990) with 322,562 cases in Peru, 46,284 in Ecuador and 16,800 in Colombia. There were peaks in 1993 in Brazil (60,340 cases), Guatemala (30,821) and Mexico (10,712). By 2002 the epidemics had run out of steam; only 23 cases were recorded continent-wide.
Historically the Indian Subcontinent was the natural home of cholera. But no longer. It did not erupt during the Pakistan floods. Cases in Asia account for less than 1 per cent of the global total: 99 per cent of cholera deaths now occur in Africa. In 2008, 217,333 cases were recorded there, 68,153 in Zimbabwe. So far this year 40,468 cases have been recorded in Cameroon, Chad, Niger and Nigeria.
Large cholera outbreaks are water-borne. Contamination of unfiltered, unchlorinated drinking water with human faeces is a prerequisite. Bad sanitation helps enormously. Only 67 per cent of people in Africa have treated drinking water and only 34 per cent have proper sanitation. Conditions in Haiti are worse: even before the earthquake only 63 per cent of the population had treated drinking water and only 17 per cent had proper sanitation.
So why has cholera arrived in Haiti only now, when the conditions for an outbreak have been perfect for years? There is no simple answer. It is not known for certain how the cholera bacterium travels the world, or why it does so only occasionally; the current pandemic is the seventh since it ventured out of Bengal in 1817. There’s no need to wait for answers before seeing it off, however; latrines and chlorinated drinking water will do the job just fine.