China has worked hard to prevent and control the spread of the H7N9 influenza virus, which this winter registered its largest outbreak since first being reported in China in 2013, but greater efforts are needed against the contagious disease, said Monique Eloit, director-general of the World Organization for Animal Health.

"Controlling avian flu is very difficult, because there are different strains, and sometimes there are no symptoms in animals with the disease," Eloit said on Monday during a visit to China.

"For the H7N9 strain, China's Ministry of Agriculture developed a very comprehensive control program with different complementary measures, especially for live bird markets, which were the main sources of contamination and risk for spreading the disease," she said.