The deadly spectre of bird flu has returned to Asia, with Vietnam confirming Friday that three people have become the latest victims of the disease that claimed 24 lives across the region earlier this year.
The World Health Organisation (WHO) said further tests were needed to see if three other people who have died over the past fortnight in the communist nation from a similar illness had also been infected with avian influenza.
An official from Ministry of Health, requesting anonymity, said two more individuals were being treated in hospital for acute respiratory infections and they were also suspected of having contracted the disease.
The latest confirmed deaths take the number of Vietnamese bird flu victims this year to 19, according to the ministry. Prior to this, the last confirmed death was a 12-year-old boy who passed away on March 15.
Eight people have also died in Thailand but the last death in the kingdom occurred on March 12.
Hans Troedsson, the WHO's representative in Vietnam, said the health ministry had informed him preliminary tests showed the presence of the lethal H5N1 strain of bird flu in one of the victims.
So far the two others have only been tested for the H5 virus. H5N1 is the only strain known to pass from infected poultry and cause illness in humans.
The UN health agency described their deaths as a worrying development that "confirmed the continuing ability of the virus to transmit to humans".
"Every human case raises the risk of avian and human viruses mingling, and the development of a pandemic strain," Peter Cordingley, spokesman for the WHO's Western Pacific Office in Manila, told AFP.
"Outbreaks in poultry are not under control. The virus is widespread in the environment and will take concentrated efforts over a long period to remove it."
Vietnam was widely criticised for acting prematurely and recklessly when it announced on March 30 that the country was free of the disease.
The WHO urged all Asian governments to exercise maximum caution and surveillance.
Thailand, Indonesia and China have all recently reported new cases following the worst of the H5N1 outbreaks earlier this year that crippled poultry industries and resulted in the deaths or culling of almost two million birds.
South Africa is currently tackling the milder H5N2 strain.
Vietnam's Ministry of Health said one of the three latest victims, a four-year-old boy from the northern province of Ha Tay, had died on August 2 in Hanoi's Central Paediatric Hospital one week after being admitted.
The second, a baby girl less than one-year-old and also from Ha Tay, died on August 4, two days after being admitted.
The third victim, a 23-year-old woman from the southern province of Hau Giang, south-west of Ho Chi Minh City, was admitted to hospital in neighbouring Can Tho province on July 31.
She died on August 2 and a throat swab sample taken from her tested positive for H5N1 at the Ho Chi Minh City-based Pasteur Institute.
Meanwhile, a health ministry official said a 19-year-old woman from Hau Giang and another person from nearby Tra Vinh province were being treated at a hospital in Ho Chi Minh City for suspected bird flu.
Vietnamese Prime Minister Phan Van Khai has ordered a nation-wide alert and the culling of all poultry in areas where the virus is detected.