HK Says Baby Girl Infected By H9N2 Bird Flu Strain

H9N2, a virus seen mostly in birds, has previously infected at least four children in Hong Kong.

Hong Kong on Tuesday confirmed a two-month-old baby girl was infected with the H9N2 bird flu strain, the fifth human case in the city since 1999, a government health official told reporters.

"Today the Center for Health Protection confirmed one human case of influenza H9N2 infection, affecting a two-month-old baby girl," said Thomas Tsang, controller for the Center of Health Protection, adding the infant was in a stable condition.

While countries around the world may be preparing for a possible H5N1 bird flu pandemic, a team of researchers said in August 2008 that the H9N2 also poses a threat to humanity.

H9N2, a virus seen mostly in birds, has previously infected at least four children in Hong Kong, causing mild illness, and is found in birds, pigs and other animals in Europe and Asia.

The team of scientists from the University of Maryland, St. Jude's Children's Research Hospital in Memphis and elsewhere tinkered with the virus and tested it in ferrets, animals whose biology is very close to humans when it comes to flu.

A single mutation made H9N2 more virulent and pathogenic, and also helped it transmit more easily from one ferret to another, they reported in their study published in the Public Library of Science journal PLoS ONE.

They also mixed H9N2 with an H3N2 virus, a type of influenza virus that causes seasonal flu in people. Scientists believe that if a human or animal is infected with two strains of flu at the same time, this "reassortment" can happen in nature. The reassorted virus was easier for the ferrets to catch and transmit.

There are hundreds of strains of avian influenza viruses, but only four -- H5N1, H7N3, H7N7, and H9N2 -- are known to have caused human infections, according to the World Health Organization.