Avian flu sweeps across China

a vendor picks chickens at a wholesale poultry market in Shanghai. A spate of bird flu cases since the beginning of the year in China has experts watching closely as millions of people and poultry are on the move ahead of the Lunar New Year holiday, the world's largest annual human migration.

A spate of bird flu cases since the beginning of the year in China has experts watching closely as millions of people and poultry are on the move ahead of the Lunar New Year holiday, the world’s largest annual human migration.

China has reported more than 50 H7N9 infections in 2014 after the strain jumped from birds to people for the first time last year. The virus remains hard to catch and most cases have been linked to contact with poultry, but scientists worry that could change if it mutates into a form that allows it to spread easily among people.