Over the past five months, the killer disease has swept through southern India, Bangladesh and Nepal. The World Health Organisation (WHO), which has issued warnings throughout the region, said there was 'an ominous possibility' that over the next three years this new strain of cholera could advance beyond southern Asia to Africa, the Middle East and southern Europe. 'The really bad news,' said one international health expert, 'is that it doesn't respond to any of the old cholera vaccines.'
It is a scientific mystery how and where this new strain, Vibrio cholerae 0139, came into being. Dr Balkrish Nair, a Calcutta toxicologist who discovered it, said: 'It's extremely toxic, hardier than all other cholera bacteria and it spreads very rapidly. The chances of those characteristics coming together in one kind of cholera organism were probably a trillion to one, but it's happened.'
Although first detected in Madras, southern India, last November, the bacterium is now known in laboratories around the world as Bengal cholera, because its impact there has been most devastating. In India's West Bengal state, the official death toll is put at 800, but some health experts claim that the government is suppressing the true figures to stem panic. The fatalities, according to one prominent Calcutta physician, Dr Bishnu Mukherjee, are probably closer to 3,000, with at least as many deaths in neighbouring Bangladesh.
West Bengal's swampy, tropical delta of the Ganges has long festered with cholera. It was first noted by India's Hippocrates, Charaka, in the fourth century. Many early British colonisers succumbed to cholera, which they blamed on foul vapours. Six other cholera epidemics this century, some of which reached as far as Latin America and Europe, all originated in the Ganges delta. Scientists claim this new strain could be the most virulent yet.
Deprived of any medical antidote, panicked Bengalis are turning to superstition: idols of the cholera goddess, Shitula, portrayed as a benign-looking woman riding a donkey, have begun to appear in many slums and neighbourhoods hit by the disease.
The macabre scene inside Calcutta's Infectious Disease Hospital, where more than 22,000 cholera victims were admitted last month, may soon be commonplace in many cities and countries throughout the developing world, once the new disease spreads.
A notice in the entrance hall reads: 'No fee is charged in this hospital for treatment of patients'. Because treatment is free and the staff do not demand bribes, as is the case in most Indian state hospitals, Calcutta's slum-dwellers, who gather water from the Ganges and from the many stagnant ponds around the city, have been swarming to the Infectious Disease Hospital.
Many have been carried in by their relatives; those who had a few rupees came by rickshaw, with an intravenous tube already plugged into their arms. They were sunken-eyed, weak and severely dehydrated.
'During the worst of it last month,' said Dr B K Das, the hospital superintendent, 'we had 500 cholera cases arrive in one day, and our hospital has only 700 beds. We had to put them in the corridors, everywhere. They were four to a bed. I've never seen suffering on such a scale.'
The onset of cholera is frighteningly subtle. Initially there are no convulsions, cramps or fevers. Often, in its earliest stages, it is wrongly diagnosed as simple food poisoning. But then, severe diarrhoea hits and, within nine hours, the victim can die of liver failure and dehydration.
If the victim is treated immediately and pumped with massive quantities of fluids to replace those lost through diarrhoea, the disease is seldom fatal. But, as Dr Nair explained, 'if someone's child wakes up in the middle of the night with diarrhoea and no other complaints, the parents probably won't do anything until the next morning, and by then it can be too late.'
'The bacterium is small,' said Dr Nair, holding up a culture dish smeared with millions of orange- coloured bacteria, 'but its desire to survive is as strong as a human's. So far, it has stayed a step ahead of us.'
After Dr Nair and his researchers first identified the strain in a sample sent from Tamil Nadu, it surfaced a month later in the Bangladeshi town of Varisal. In December, more than 100,000 Muslim pilgrims descended on Varisal for a religious festival, and Dr Nair believes southern Indian travellers could have transmitted it. Now, the bacteria are firmly entrenched in West Bengal's thousands of waterways and ponds. 'The Ganges is supposed to be sacred and pure,' Dr Gosh, an epidemologist, said, 'but I'm afraid it is contaminated too.'
In India, Vibrio cholerae 0139 has been detected in the southern states of Tamil Nadu, Kerala, and Andhra Pradesh. Inevitably, cholera will soon besiege India's capital, Delhi, and Bombay. 'Back in November, we thought it would be only a small outbreak,' Dr Nair said. 'We never imagined that it could be the next big epidemic. It moves so rapidly.'
Even if travel restrictions were imposed on the cholera-hit region, it would merely slow, but not stop, the fatal bacteria's advance. More than 1 billion people live in southern Asia. Thousands fly in and out every day, and such seaports as Bombay, Madras and Karachi are among the busiest in the world.
As one scientist working for an international health agency in Delhi pointed out: 'All it takes is some fellow who gets off a bus and craps in a stream. Someone in a village farther down drinks it, and you have an outbreak of cholera.' A few cases of Bengal cholera have been identified in Malaysia and Japan. A cargo of Bangladesh seafood sent to Japan was also found to contain the lethal bacteria.
The biggest nightmare among scientists is that the new cholera breed may move into Africa, where water and sanitation systems are even worse than in southern Asia. Cholera is found in 54 countries, and in 1992, more than 500,000 cases were reported. This year, the figure may even double, according to some scientists who guess that within two years the number of cholera fatalities may increase tenfold.
The old cholera vaccine was developed from bacteria killed by heat, so that the human body could recognise the harmless cholera and ready its defences. However, it is only 58 per cent effective and has severe side-effects. Over the past 10 years, millions of pounds have been spent in a fruitless search for a new, more potent vaccine.
'The research projects will have to start again from scratch,' said one medical expert, who explained that in ponds where the both the micro-organisms are present, the new Bengal strain invariably overpowers the older El Tor bacteria.
Dr Nair argues that work should begin urgently on a new Bengal cholera vaccine, using the discarded heat method. 'Even if it's only 50 per cent effective,' he said, 'half of a million is still a lot of lives.'