Four family members in Thai northern province of Phitsanulok are suspected to be infected with avian flu after they ate a dead duck from their farm, Thai local media reported on Thursday.

Thawatchai Kamoltham, the Phitsanulok provincial health chief, said Thursday that four members of a family in Phitsanulok fell sick after eating a dead duck recently. Since their symptoms are similar to those of the deadly H5N1 bird flu virus, they are now been isolated in a nearby hospital.

Local health authorities had declared the duck farm in Tortae sub-district of Phitsanulok off-limits for two weeks as a precaution. About 600 ducks in the farm have been slaughtered, Thawatchai was quoted by the Bangkok Post as saying.

It is reported that there are also about 30 pigs in the farm which may have contracted bird flu.

Thawatchai disclosed that there are many herds of free rang ducks within one kilometer radius from the farm which need to be closely monitored.

Meanwhile, the Ministry of Public Health has instructed all provincial health officials to keep close watch on bird flu outbreak in their respective provinces now and in the next two months, which are considered as risky period when bird flu usually spreads out.