Health workers in Nepal are to cull thousands of chickens following the discovery of the H5N1 strain of bird flu in the southeastern part of the Himalayan country, officials said Sunday.

"We sent samples for investigation to London after chickens started to die of a mysterious disease in commercial poultry farms," said Ram Krishna Khatiwada, of the government's Directorate of Animal Health.

"We have received the test reports today that confirms infection of bird flu in poultry farms in Khanar and Ithari of the Sunsari district."

Bird flu has also been confirmed in the eastern hills of Panchathar district and the tea-producing area of Ilam, Katiwada told AFP, adding that surveillance of farms was to be stepped up and 4,000 chickens would be killed in the affected areas.

"There has not been infection to humans in the area so far," he added.

"Some have complained of itching and vomiting but that is only panic. We will get the situation under control in one or two days."

Nepal's first reported outbreak of bird flu in poultry was in January 2009 in the eastern part of the country.

The virus reached the capital Kathmandu for the first time in December last year, with health workers culling hundreds of chickens and ducks.

If it spreads to humans, bird flu can cause fever, cough, sore throat, pneumonia, respiratory disease and sometimes death.