Pig flu: warnings the world ignored:
A team led by Dr Gregory Gray at the University of Iowa College of Public Health has long been investigating the risks of viruses jumping from animals to people. In November 2005, they published a major study in the scientific journal, Clinical Infection Diseases.
It pointed out that an enormous shift had taken place in pig farming in the US over the last 60 years. In 1965 there were more than a million farmers with an average of 50 pigs each, but now there are only 50,000 farmers with an average of 900 pigs each.
In Iowa there are nearly nine times more pigs than people, with 25 million hogs a year raised at 9,300 farms.
"The potential for animal-to-animal transmission will be much greater than on a traditional farm because of the pigs' crowding resulting in prolonged and more frequent contact," it argued.
"In addition, virus-laden secretions from pigs may be more concentrated, and reductions in ventilation and sunshine exposure may prolong viral viability."
The study warned swine workers could "initiate epidemics" by mixing viral strains which would then trigger a pandemic. "They may serve as a conduit for a novel virus to move from swine to man or from man to swine," the study said.
"One might envision that, once a novel virus is introduced into a densely populated swine barn, the viral loads swine workers would experience could overwhelm any partial immunity they might possess. After work, they may readily communicate that virus to their family members and neighbours."
Gray and his colleagues uncovered evidence that swine flu was widespread in farmers, meat processing workers and vets. They also pointed out that the infection now occurred all the year round in pig farms, instead of just seasonally as in the past.
Swine flu has disturbing echoes of bird flu H5N1. Its epicentre was the intensive poultry farms of Asia. One theory is that H5N1 originated at Qinghai Lake in northern China which is surrounding by intensive poultry farms whose "poultry manure", a euphemism for what is scraped off the floor - bird faeces, feathers and soiled litter - was used as feed and fertiliser in fish farms and fields around the lake. Worldwide, intensive poultry production, like pig meat production, has exploded and this growth has been mirrored by an increase in avian flu. In southeast Asian countries, where most of the H5N1 outbreaks are concentrated - Thailand, Indonesia and Vietnam - production has jumped eight-fold in just three decades as cheap chicken meat has become an international commodity. Thai chicken, for instance, is a common ingredient in many UK ready-meals. They don't yet contain Mexican pork, but if our taste for cheap foreign meat persists, anything is possible.