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

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

China recorded 192 human H7N9 cases, including 79 deaths in January. In January 2016, there were 28 cases, including five deaths, according to the National Health and Family Planning Commission, China's top health authority.

The number of cases fell to 160 in February and 96 in March. Experts from the Chinese Center for Disease Control and Prevention said the disease, which peaks in winter, was expected to drop off in late April.

Last year, China began taking measures against the virus, such as closing live poultry markets in provinces heavily hit by the virus such as Anhui and Hunan.

"I believe China significantly improved its capacity to control the diseases in animals," Dr Eloit said.

"Unfortunately, avian flu is a very contagious disease, so if it is not controlled at the source it is a risk for humans and for other countries... because of global trade. Improvement of the control programme, and also improvement in transparency... should be the two main pillars of the Chinese strategy," she said.

Efforts also should be adapted to changing situations. "The virus strain can change because sometimes wild birds are also infected," she said.

While H7N9 generally is not transmitted from person to person, the World Health Organization has called for more vigilance in China and stressed the possibility that the virus may adapt to "facilitate efficient, sustained human-to-human transmission."