'It's not out of the question, but if it does happen, it would be associated with non-commercial poultry, not with commercial poultry,' he says.

In Asia the risk of a large outbreak is greater because of the lack of control, he says.

'On the other hand, you can with relatively simple control measures get the number down to only a few [infected] flocks.'

Morris thinks North America is probably already infected or is close to becoming infected, but that it will not be detected for some time.

InterSpread Plus is built using Visual Basic and C++. The GIS (geographic information system) is built inside Microsoft Access, says Morris.