An official said that bird flu outbreaks in Nepal, which have not yet been controlled, mainly spread due to unverified vaccines being administered haphazardly to chickens by poultry farmers.
Poultry farmers imported and used the vaccines haphazardly without first consulting the government's veterinary doctors, Narayan Ghimire, spokesperson of the government's bird flu control campaign, told Xinhua.
As the vaccines were unverified, the virus grew so rapidly that it became difficult to control, said Ghimire.
Experts said that before injecting a particular vaccine that contains a small amount of bird flu virus, first the species of flu present in a fowl has to be determined.
If one type of vaccine is administered in a fowl infected with another type of bird flu, the vaccine suppresses the symptoms of the disease for a short period. In the long run, the virus spreads both in quantity and quality.
A team of experts from the Food and Agriculture Organisation (FAO) and the World Health Organisation (WHO) would also visit Nepal soon to study the problem and suggest remedial measures.
"We will be able to recommend the appropriate vaccines, only after the team submits its final report," an official said.
Since mid-July, at least 40 bird flu cases have been reported in the Kathmandu valley, while more than 30 cases have been reported from nearby Bhaktapur.
Following the outbreak, the government imposed a one-week ban on sale and supply of chicken products Aug 1-7. The ban has been lifted, but cases of bird flu are still emerging in various poultry farms in the capital.