BEIJING - China's Ministry of Agriculture said Wednesday that epidemiological investigations have found no H7N9 bird flu infections in animals.

Experts from the ministry said it remained unknown where the virus came from and how it had spread.

Data from the ministry showed that a total of 25 H7N9 bird flu strains have been detected in wild birds around the world and that the virus had not been found in poultry.

Strains can be transmitted globally by migratory birds and have been detected in North America and Eurasia, said experts. China is on the migratory flyway of virus carriers and at great risk of infections, they said.

After reports of human infections in east China's Shanghai, Anhui and Jiangsu, the ministry immediately organized epidemiological investigations in animals in these regions, said a ministry official, adding that sample collection and detection work is underway.

Two more infections of the H7N9 bird flu, involving one death, were reported in the eastern Zhejiang province, bringing the total number of  infected people in the country to nine, local authorities said Wednesday.