Bird flu may be spread by using chicken dung as food in fish farms, a practice now routine in Asia, according to the world's leading bird conservation organisation.
Fertilising fish ponds with poultry faeces, which can dramatically improve fish growth, may set up major new reservoirs of avian influenza infection if the chickens providing the manure are infected themselves, according to BirdLife International, the Cambridge-based umbrella body for bird protection groups in 100 countries.
The suggestion, which has echoes of the BSE outbreak in Britain - when cattle were infected by their food - puts a question mark over a technique firmly backed by the UN's Food and Agriculture Organisation (FAO) as a primary means of providing protein for mushrooming populations in developing countries.
Known as integrated livestock-fish farming, the technique involves transferring the wastes from raising pigs, ducks or chickens directly to fish farms. At the right dosage, the nutrients in the manure give an enormous boost to the growth of plankton in the ponds, which are the main food of fish such as carp and tilapia.
BirdLife International is now calling for an investigation into the possibility that thousands of manure-fed ponds across Asia may be the means by which the new potentially deadly strain of avian influenza, H5N1, is being spread. BirdLife points out that outbreaks of H5N1 have occurred this year at locations in China, Romania and Croatia where there are fish farms.
The Chinese outbreak of H5N1 in May, which mainly involved bar-headed geese, took place at Qinghai Lake, a location where the FAO helped establish an integrated livestock fish farm in the early 1990s, BirdLife said.
"This outbreak helped lead to the widespread media speculation about wild birds spreading H5N1," said Richard Thomas from BirdLife. "We pointed out that bar-headed geese migrate from India, where H5N1 has never occurred, and migrate early, so they must have contracted the disease locally, at Qinghai."
Although no mention has been made of the possible links between manure-fed ponds and influenza in the recent alarm over bird flu, the issue has been raised before, and the FAO, although actively promoting the technique, is well aware of the threat.
Its 2003 report, Integrated Livestock Fish Farming Systems, noted: "Recently, livestock and fish have been implicated in the irregular occurrence of influenza pandemics; the global impacts on public health of promoting livestock and fish integration are huge if these claims are substantiated."
In fact, the FAO may have been aware for very much longer that some scientists think there is a risk. The 2003 report includes a reference to a paper published in the journal Nature in 1988. This paper, by Christoph Scholtissek from the University of Giessen in Germany and Ernest Naylor from the University of Bangor in Wales, was titled Fish Farming and Influenza Pandemics. It said that bringing together fish farms with farm livestock "may well be the creation of a considerable human health hazard".
However, the FAO has continued to promoted integrated livestock fish farming actively throughout the ensuing period.
BirdLife's director Dr Michael Rands said: "We are not aware that people have confirmed that that is a likely cause - but people have suggested it. If it's a possibility, and if it presents a serious human health risk, it certainly ought to be researched, and if it has been researched, the research should be out there for us all to see."
* A village in Romania has been quarantined after five chickens there tested positive for the H5 variant of bird flu, the head of the country's National Animal Health Agency has said.
The virus was detected on Friday in the village of Albesti, 62 miles east of Bucharest. The virus was also confirmed in the nearby village of Stelnica. Samples will be sent to Britain for further tests.