Japan reported its first case of bird flu in a human on Wednesday - a man who got the disease from birds.

　　Although there has been no evidence of human-to-human transmission, experts worry that the virus could mutate into a version easily spread among people, setting off a global pandemic.

　　The man caught the bird flu virus while disinfecting a contaminated poultry farm in western Kyoto during an outbreak in Japan earlier this year, the Health Ministry said.

　　The ministry took blood samples from about 86 people who may have been exposed. One tested positive for antibodies for the disease, confirming the infection. Four others may also have been infected but the tests were inconclusive.

　　It was the first confirmed case of human infection from the disease in Japan, the ministry said in a statement, adding that the man showed no symptoms other than a headache that lasted several days.

　　It wasn't clear how the five were exposed to the virus. One said he hadn't worn a mask at the farm even after the virus was discovered there, the ministry said.