The brother of a boy who died last week from bird flu has tested positive for the virus, Cambodia's Health Ministry has said.

The 9-year-old's death in the northeastern province of Kratie was the first from bird flu in Cambodia this year, after four were reported last year by the World Health Organisation.

Bird flu, also known as avian influenza, normally spreads in poultry and wasn't deemed a threat to people until a 1997 outbreak among visitors to poultry markets in Hong Kong.

Most human cases have involved direct contact with infected poultry, but there have been concerns that the virus could evolve to spread more easily between people.

The WHO and the UN's Food and Agriculture Organisation this month warned that Lunar New Year festivities celebrated in much of Asia posed an increased risk of spreading the virus.

In a statement, Cambodia's Health Ministry said the 16-year old brother tested positive for the virus on Sunday but exhibited no symptoms. The boy was undergoing medical treatment, and officials are investigating who had contact with the brothers and how and where they contracted the virus.

The Health Ministry said the boy who died last week fell ill with fever, shortness of breath, coughing and fainting after eating a meal his parents had cooked from chicken and ducks they raised.