Chinese authorities said Wednesday that a 73-year-old Chinese woman died after being infected with a bird flu strain that had sickened a human for the first time, a development that the World Health Organization called “worrisome.”

China’s Centre for Disease Control and Prevention confirmed the woman in the city of Nanchang had been infected by the H10N8 bird flu virus, a strain that had not previously been found in people, the Jiangxi province health department said on its website.

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This is the second new bird flu strain to emerge in humans this year in China. In late March, the H7N9 bird flu virus broke out, infecting 140 people and killing 45, almost all of them on the mainland. The outbreak was controlled after the country closed many of its live animal markets — scientists had assumed the virus was infecting people through exposure to live birds.

Timothy O’Leary, spokesman for the World Health Organization’s regional office in Manila, said WHO officials were working closely with Chinese authorities to better understand the new virus. He said though its source remains unknown, birds are known to carry it and it would not be surprising if another human case was detected.

“It’s worrisome any time a disease jumps the species barrier from animals to humans. That said, the case is under investigation (by Chinese authorities) and there’s no evidence of human-to-human transmission yet,” O’Leary said by phone.

In the new case, the Jiangxi health department said the woman had severe pneumonia before dying Dec. 6 in a hospital in Nanchang.

She had suffered high blood pressure, heart disease and other underlying health problems that lowered her immunity, the health department said. Her medical history showed that she had been in contact with live poultry.

The health department said “no abnormalities” have been found in people who had close contact with her. It did not say if they had been tested or quarantined, though China has in previous outbreaks taken those measures.

Experts are cautious when it comes to bird flu viruses infecting humans. They have been closely watching the H5N1 bird flu virus, which has killed 384 people worldwide since 2003. The virus remains hard to catch with most human infections linked to contact with infected poultry, but scientists fear it could mutate and spread rapidly among people, potentially sparking a pandemic.