YANGON, Aug 1 (Reuters) - Myanmar found its second bird flu outbreak in July on a farm northwest of the commercial capital Yangon, the U.N. food agency said on Wednesday.

"About 3,800 chickens have been culled as part of the measures to control the situation," Tang Zhengping, country representative of the Food and Agriculture Organisation, told Reuters.

The virus was detected on July 26 on a poultry farm in Letpadan Township, about 80 miles (130 km) northwest of Yangon, he said.

The OIE, the global organisation for animal health, reported an outbreak among chickens in Mon State in southern Myanmar on July 24.

India, which shares a 1,600-km (1,000-mile) border with the former Burma, said this week it had stepped up surveillance to stop poultry smuggling from its neighbour.

The H5N1 strain remains largely a bird virus but experts fear it might mutate into a form that easily passes between people, setting off an influenza pandemic in which millions could die.

The virus is known to have infected at least 319 people worldwide since 2003 and has killed at least 192, according to the World Health Organisation.