As the deadly H5N1 virus spread rapidly in the past six months from Asia into parts of the Middle East, Europe and Africa, specialists have been trying to work out how it travels.

Some suggest wild migrating birds are the main carriers, others point to poultry trade as the major force behind the virus's spread.

"Do we have a permanent reservoir (of the virus) in wild birds or not? It still remains a question," FAO's Chief of Animal Health Services Joseph Domenech told Reuters after the conference attended by over 300 scientists from 100 countries.

He said one of the main achievements of the conference, organised by FAO and World Animal Health Organisation (OIE), was to get together people from different sectors -- from poultry trade to wildlife experts and policy makers -- and start the discussion about how bird flu travels on long distances.

"We have identified the gaps and the need to continue and intensify research, in particular with regards to the species which can be involved (in spreading the virus)", Domenech said.

He said global surveillance of wild birds should be boosted to gather more information.