More bird flu cases in Vietnam, H5N1 strain
There have been 41 cases of bird (avian) flu in Vietnam over the last four months - of which 16 have been deadly.
This present strain is becoming less virulent but spreads faster, apparently.
What is bird flu?
Bird flu or avian influenza is a contagious viral infection that can affect all species of birds. In intensive poultry rearing systems young fattening turkeys and laying hens are usually the most affected.
Free-living birds may carry influenza viruses without becoming ill due to a natural resistance. Wild waterfowl such as ducks can have the virus without being ill but can transmit the virus to domestic (not wild) poultry.
What causes it?
The virus which causes bird flu is an Influenzavirus A virus of the family Orthomyxoviridae. Influenza A viruses infecting poultry can be divided on the basis of their ability to cause disease (pathogenicity).
The very virulent viruses cause highly pathogenic avian influenza (HPAI).
Other AI viruses cause a much milder disease (low pathogenic avianinfluenza, (LPAI). Signs of sickness are much less evident or even absent and far fewer birds die.
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