A highly contagious strain of avian flu is spreading across West Africa,decimating poultry farms and stoking fears the virus will jumpfrom birds to humans, the UN’s food agency warned on Monday. Markets and farms in Nigeria, Burkina Faso, Niger, Ivory Coast and Ghana have been hit with the deadly H5N1 virus over the past six months, the UN’s Food and Agriculture Organisation (FAO) said.

If the virus continues to spread, it could affect more than 330 million people across West Africa, hurting food security and human health in a region still recovering from the Ebola crisis. “Urgent action is needed to strengthen veterinaryinvestigation and reporting systems… to tackle the disease at the root, before there is a spillover to humans,” Juan Lubroth, head of the FAO’s animal health division, said in a statement.

In Nigeria alone, 1.6 million birds have been killed by the virus or culled to stop its spread since last year, the FAO said, damaging the economy and robbing citizens of a relatively cheap source of protein. H5N1 bird flu first infected humans in 1997 in Hong Kong. Ithas since spread from Asia to Europe and Africa and has become entrenched in poultry in some countries, causing millions of poultry infections and several hundred human deaths.

Other West African countries including Benin, Cameroon, Maliand Togo have not identified bird flu cases and need to continue monitoring the situation to help prevent its spread, the FAO said. Local veterinary officials have been urged by the UN to try to trace where infected animals were sold to find sources ofthe outbreak in order to halt its spread. Poultry production has grown rapidly across West Africa in the past decade, the Ivory Coast alone has seen output expand bymore than 60 percent, but regulatory systems haven’t kept pace, the FAO said.

The organisation is asking donors for $20 million to respond to the avian flu outbreak and to help prevent its spread.