2009年5月1日 星期五

H1N1 的來源 ?

www.guardian.co.uk

The growing concern over the H1N1 swine flu virus – a particularly alarming combination of swine, avian, and human viruses which has now reached the UK – seems to have come almost out of nowhere. The World Health Organisation (WHO) is now calling the virus, which has infected an estimated 1,000 people and killed around 150 in Mexico, an "international public health emergency" that could reach global pandemic levels.

But as Dr Michael Greger, director of Public Health and Animal Agriculture at the Humane Society of the United States, has pointed out, this is not the first time a triple hybrid human/bird/pig flu virus has been uncovered. The first was found in a North Carolina industrial pig farm in 1998, and within a year it had spread across the United States.

With discoveries of the current virus now being made as far afield as Scotland and New Zealand, questions are being asked about how it could have developed, and what can now be done to protect the global population from future outbreaks.

Dr Greger has highlighted how some experts blamed the emergence of the original 1998 virus on intensive farming practices in the US, where pigs and poultry are raised in extremely cramped conditions, in adjacent sheds – and tended to by the same staff.

North Carolina has the densest pig population in North America, with around twice as many swine mega-factories as any other state. In 1998, North Carolina's pig population had hit ten million, up from two million just six years before. Yet the number of hog farms was decreasing, with more and more animals being crammed into fewer and fewer farms. Since the primary route of swine flu transmission is thought to be the same as human flu, the increased potential for the spread of disease in such conditions is clear.

More research is urgently needed to explore the potential link between industrialised animal farming, and the spread of disease. Some elements of the Mexican media are already pointing to the potential role of intensive pig farming in Mexico, which has grown substantially in recent years, with some giant operations raising tens of thousands of pigs at a time.

Since news of the epidemic broke, reports in Mexico City daily La Jornada and Veracruz-based paper La Marcha have detailed how a number of community residents in the affected areas have expressed concerns over the operations of Smithfield Foods, the world's largest pork packer and hog producer. According to these reports, in Veracruz – where the outbreak originated, a Smithfield subsidiary called Granjas Carrol raises 950,000 hogs per year in intensive conditions.

Smithfield has released a statement denying any link between the outbreak and Granjas Carrol's operations in Mexico. It said the company routinely administers influenza virus vaccinations to its herds and conducts monthly tests for the presence of swine influenza. It said it had found no clinical signs or symptoms of swine influenza on its farms.

This is not the first time intensive, industrialised agriculture has been accused of spreading disease. Recent avian flu outbreaks, for example, have shown the extent to which the export-oriented corporate model of poultry production may have spread strains such as H5N1. In my report Avian flu: time to shut the intensive poultry flu factories? of 2006, I outlined how bird flu has been endemic in wild birds in much of the world without leaping the species barrier and causing people any harm.

But in damp and cramped conditions, a series of mutations can occur resulting in a highly pathogenic form. Within crowded chicken factory farms, the mild virus can evolve rapidly towards more dangerous and highly transmissible forms, capable of jumping species and spreading back into wild birds, which are defenceless against the new strain.

Experts are increasingly warning that the practices of intensive farming must be reviewed and regulated. While it will be difficult to reach any firm conclusions about this current outbreak of swine flu until more details emerge, it is crucial that the authorities undertake an urgent inquiry, in order to better understand the development and spread of animal-based epidemics which can be lethal to humans.

• Caroline Lucas is Green party MEP for the south-east of England

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