(Recasts, adds byline, details)

By Kamil Zaheer

NEW DELHI, Aug 3 (Reuters) - India has quarantined 51 people in the remote northeastern state of Manipur following an outbreak of the H5N1 strain of influenza in chickens last month, a senior official said on Friday.

"Since all these people had worked in culling or sanitising operations or monitoring people's health around the affected poultry farm they have to be quarantined and monitored," said Vineet Chawdhry, joint secretary in the health ministry.

Most had complained of being "unwell", he added, but did not say whether any had flu-like symptoms.

All 51 were on Tamiflu, the popular drug to prevent and treat bird flu, as a precaution, the health ministry said.

Hundreds of cullers were involved in killing nearly 300,000 fowl over the past week in Manipur, a state bordering Myanmar that saw two outbreaks of bird flu in chickens in July alone.

The culling, which took place within a 5-km (3-mile) radius around the affected poultry farm near Imphal, capital of Manipur, ended on Thursday.

Health officials have completed checks of around 235,000 people in the area, but said they would closely monitor the situation.

Globally, the H5N1 virus has killed at least 192 people out of 319 who have been affected since late 2003, with health experts fearing it could one day mutate into a form that could pass easily between humans, triggering a pandemic.

On Friday, authorities cleared four boys who had been suffering from fever after handling dead or sick poultry in Manipur.

But officials in Tripura, another northeast Indian state, were on alert after around 500 chickens died in a commercial poultry farm in a district bordering Bangladesh, where avian flu has spread to a number of areas this year.

Officials said blood and tissue samples had been sent for testing, but added they suspected the deaths to be caused by infectious bursal disease, a viral illness, along with coccidiosis, a parasitic illness found in animals.

Western India had two major outbreaks of the H5N1 virus in chickens last year, but has not yet reported any human case. (Additional reporting by Biswajyoti Das in Guwahati) (Editing by Nita Bhalla; Reuters Messaging: kamil.zaheer.reuters.com@reuters.net: +91-11-4178 1000))

AlertNet news is provided by