NEW DELHI, India (CNN) -- India has culled more than 4,000 birds in Sikkim since the outbreak of avian influenza in the remote northeastern state last week, federal authorities said Thursday.
Health officials also detected dozens of cases of upper respiratory infection among humans, but none of the patients had any history of handling sick poultry, a government statement said.
Sikkim, which borders Nepal and China, declared a bird flu outbreak on January 19.
"So far, 4,129 birds have been culled," the federal health ministry said, announcing that operations were now over.
Sikkim is the third Indian state to report a bird-flu outbreak recently after Assam and West Bengal.
There has been no case of human infection so far, according to health authorities.
Since the end of 2003, the H5N1 virus has infected numerous species of birds in more than 60 countries in Asia, Europe and Africa. It has not been found in birds in North or South America or the Caribbean, according to the United Nations' Food and Agriculture Organization.
Human-to-human transmission of avian flu is rare, but in some cases the virus has passed from poultry to humans. It has killed more than 200 people since 2003.