Bird flu has infected five more people in Vietnam, two of whom are under treatment in Ho Chi Minh City where riot police are manning checkpoints for poultry vehicles and authorities have issued warnings to travel agents.

A researcher at the city’s Pasteur Institute told Reuters on Friday tests had confirmed the poultry virus had infected two girls, a 10-year-old from Long An province and a 13-year-old from Dong Thap province.

“We tested the 13-year-old girl three times and found the H5 component in her samples,” said the laboratory researcher, referring to the killer H5N1 poultry virus strain.

Her mother died on Jan. 21, also from the H5N1 virus, doctors said.

Tests on three men, aged between 30 and 66 who are now being treated at a Hanoi hospital, also confirmed they were infected with the poultry virus, the Tuoi Tre (Youth) newspaper said, citing lab tests.

The five new cases bring Vietnam’s total number of human infections to 16 in the latest wave of the virus which first surfaced in the southeast Asian nation in December 2003.

Of these cases, nine have died in recent weeks. Including the 12 people who died of bird flu in Thailand last year, Asia’s total death toll now stands at 41.

Officials in Ho Chi Minh City, a sprawling metropolis of 10 million people, said riot police would now be joining market inspectors at poultry van checkpoints set up around the city to stop the virus spreading.

The city’s tourism department has also asked tour agents to stop taking visitors to areas where the risk of poultry virus infection is high, the Saigon Giai Phong daily said.

Most of the victims are believed to have caught the virus from infected poultry but doctors fear it could mutate into one that is easily passed between people, unleashing a global human flu pandemic that could kill millions.