The case of a father and daughter in China who both became infected with H7N9 bird flu provides the strongest evidence yet that the virus can transmit from person to person, experts say.
The father, a 60-year-old living in the Jiangsu province of eastern China, fell ill about five to six days after he visited a live poultry market in March, according to a new report that details the case today (Aug. 6) in the British Medical Journal.
The man's 32-year-old daughter, who became ill about two weeks later, did not visit poultry markets, but did spend several days caring for her sick father before he was admitted to the hospital.
Both patients became severely ill, developing fevers and pneumonia, and later died from the disease. [See 6 Things You Should Know About the New Bird Flu]
Genetic testing revealed that the patients were infected with nearly identical strains of H7N9.
The most likely explanation for these cases is that the father became infected with H7N9 from a poultry market (or the poultry he purchased there), and then he passed the virus directly to his daughter, according to the researchers, at theJiangsu Province Centre for Disease Control and Prevention. This is the first detailed report of probable human-to-human transmission of H7N9, the researchers said.
Cases of H7N9 first appeared in China in March, and so far 133 people have become ill, including 43 who have died. The majority of cases appear to be unconnected to each other.
The new report does not mean that H7N9 is getting closer to causing a pandemic in people, James Rudge and Richard Coke, of the London School of Hygiene and Tropical Medicine in Bangkok, Thailand, wrote in an editorial accompanying the report in the journal.
Limited human transmission of bird flu viruses has been seen in the past, and is not surprising, Rudge and Coke said. Some animal studies also suggested that H7N9 can spread between mammals. But so far, the virus does not appear to spread efficiently — there is no evidence of sustained human-to-human transmission with H7N9, Rudge and Coke said.
In the case of the father and daughter, the daughter was deeply involved in caring for her father — she cleaned up his mucus, and she cleaned his teeth without using protective equipment, according to the report.
Of the 43 people who came into contact with the father and daughter before and during the time they were ill, none became infected with H7N9, the report said.
Still, H7N9 is concerning. The virus does not cause symptoms in birds, so it can spread undetected within poultry populations, Rudge and Coke said.
The report provides "a timely reminder of the need to remain extremely vigilant," Rudge and Coke said. "The threat posed by H7N9 has by no means passed."
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.