By Ho Binh Minh

HANOI, July 23 (Reuters) - Two people have died in northern Vietnam from a virus that has killed thousands of pigs in recent weeks while bird flu has returned to the central region, killing hundreds of ducks, government and media reports said.

Twenty two people, most from northern areas, have been taken to a Hanoi hospital so far this year after they fell sick from the Porcine Reproductive and Respiratory Syndrome (PRRS) virus, the Vietnam News Agency said on Monday.

Two of the infected had died, it said without giving more details.

On July 14, Agriculture Minister Cao Duc Phat said more than 16,000 pigs had been infected by the virus, also known as Lelystad virus, in the central province of Quang Nam since June 25.

"The disease in Quang Nam now is very serious, it is spreading wide and risks to infect other provinces and cities," Phat said in a letter circulated to provincial authorities nationwide, a copy of which was seen by Reuters.

He said the transport of pigs and pork from infected areas must be banned to help halt the virus spread..

The syndrome was first recognised in the United States in the mid 1980s and was called "mystery swine disease". In some other countries including Vietnam it is referred to as "e;blue ear disease"e;.

People infected by the virus suffer from rapid internal haemorrhage and high fever after they eat pork from a sick pig or inhale the air near the sick swine, doctors said.

Since late June the virus has spread to neighbouring Quang Ngai province and Danang city, infecting more than 27,000 pigs, nearly 1,500 of them had died, the Animal Health Department said.

On Sunday state-run Vietnam Television said pig raisers in Quang Nam province had thrown hundreds of dead pigs into a local river, causing serious water pollution near the UNESCO-recognised tourist town of Hoi An.

BIRD FLU KILLS DUCKS

The Animal Health Department said bird flu returned to the central region killing 220 ducks at a farm province of Quang Binh last Saturday. Tests of the dead ducks showed they had the H5N1 virus, it said.

In all, bird flu infections have been detected in ducks and chickens in two northern provinces, Quang Binh province in the centre and the southern Mekong delta province of Dong Thap.

Vietnam has detected five human infections by bird flu since May, three had been cured but two others had died, the first human casualties in the Southeast Asian country since November 2005.

State media said on Monday that the Medical Military Academy would start testing the domestically produced anti-bird flu vaccines on humans from August, with the first group involving 20 volunteers.

Globally, the H5N1 virus has killed 192 people out of 318 known cases, according to the World Health Organisation, while hundreds of millions of birds have died or been slaughtered.

Experts fear the virus could mutate into a form easily transmitted from person to person and sweep the world, killing millions.