Vietnam Finds New Strains of Bird Flu Viruses
Date: 17-Nov-05
Country: VIETNAM
Author: Nguyen Nhat Lam
Dong Manh Ha, director of Ho Chi Minh City Regional Animal Health Centre, told Reuters a study conducted by the centre found new avian influenza strains of the H3 and H4 subtypes in poultry.
Scientists say strains of the H3 and H4 subtypes are capable of causing death in birds but are generally less virulent and spread more slowly than the H5 subtype they fear could trigger a human pandemic.
The H5N1 virus is endemic in poultry in several countries in Asia and has killed 64 people, including 42 in Vietnam, since late 2003. Experts fear that H5N1 could mutate into a form that passes easily among people, triggering a pandemic.
"The presence of more subtypes of the flu virus in poultry make the virus all the more dangerous," Ha said, adding that samples had been sent to a World Organisation for Animal Health (OIE) laboratory in Australia for further investigation.
State media reports said the new virus strains are H3N4 and H4N5.
HIGHLY VIRULENT
Vietnam is tackling more than a dozen H5N1 outbreaks in poultry and has stepped up culling in its two main cities. The virus is highly virulent and can kill poultry in a matter of hours. It has killed about half the people it has infected.
In the latest outbreak, an Agriculture Ministry report said 286 chickens and geese had died or been slaughtered in the northern province of Son La.
That took the number of the affected areas to 14 of Vietnam's 64 provinces since the virus returned in October.
Hong Kong infectious disease expert Lo Wing-lok said that with heightened surveillance, it was not surprising for other subtypes, such as H3 and H4, to turn up although these are not generally thought of as being highly pathogenic.
But Lo, a member of a scientific committee on zoonotic and emerging diseases in Hong Kong, said if the strains were allowed to spread in poultry, people in close contact with the birds would be at risk.
There was also the risk of these subtypes mixing and exchanging genetic material with the H5N1 virus. There would then be the possibility of the H3N4 and H4N5 strains becoming more pathogenic.
Influenza type A viruses, which include human and avian flu viruses, are categorised by H and N components, which denote specific types of proteins on their surface.
The H component governs the ability of the virus to bind to and enter cells, which become virus-making factories. The N component governs the release of the newly made viruses from the animal host cell.
There are 16 H subtypes and nine N subtypes. Human influenza viruses are usually strains of H1N1, H2N2 and H3N2 but avian flu subtypes H5 and H7 can also infect people.
Media reports said two more people in Hanoi, a 15-year-old girl and a 71-year-old woman, were in hospital with symptoms of bird flu and were being tested. The latest cases bring to five the number of suspected infections in Vietnam.
(Additional reporting by Tan Ee Lyn in Hong Kong)
