By Tan Ee Lyn

HONG KONG, Aug 17 (Reuters) - Battling a severe pig disease, Vietnam has dispatched virus samples to the United States and is poised to implement fresh measures to try to rein in the unprecedented epidemic, a government expert said on Friday.

The outbreak of Porcine Reproductive and Respiratory Syndrome (PRRS), or blue ear disease, began in Vietnam in June and is worst in the central provinces of Quang Nam and Quang Ngai, said epidemiologist Do Huu Dung of the Department of Animal Health.

Although the disease has been detected in the past in imported pigs, it has never spread on such a scale, Dung said.

At least 28,000 pigs were infected by end July, according to government statistics. And around 20 percent of these have died, epidemiologist Dung told Reuters in a telephone interview.

Experts from the Food and Agriculture Organisation arrived on Sunday to visit some of Vietnam's worst-affected sites.

"They will give a report to the agriculture minister next week. We hope they will come up with recommendations," Dung said.

Vietnam's epidemic began at a time when the disease was sweeping through many provinces in neighbouring China, whittling down pig populations and raising prices of pork there.

The disease inundated almost half of China in 2006 and China's top veterinarian said in June that the disease killed about 1 million pigs in the country last year.

TRACKING THE SPREAD

Experts are not sure how the virus, which causes high fever, still-births, appetite loss, diarrhoea and redness of the skin, got into Vietnam but they are trying to nail down its origins.

Samples of the Vietnam virus arrived on Wednesday in the United States, where they would be genetically sequenced, Dung said. Virus samples will also be sent to China for sequencing.

Such analyses enable scientists to determine how close it is to the strain proliferating in China, or if they are identical.

The genetic footprints will allow experts to postulate on the likely direction and ways the virus spread, so more targeted action may be taken to arrest its movement.

Asked if the virus may have spread to Vietnam from China, Dung said: "We cannot be so sure. You can suspect it but we will soon know about that once the gene sequencing data is available."

"We are cooperating with China on different control measures, like vaccination, and we are getting a China expert very soon."

SYMPTOMS SIMILAR TO THOSE IN CHINA

Chinese scientists said in a published paper recently that China's PRRS epidemic was caused by a new and highly pathogenic strain of the disease which caused several new and unusually severe symptoms in adult pigs.

Although a serious swine disease, PRRS usually causes reproductive failure in pregnant sows or respiratory tract distress in suckling pigs. Usually, it was the piglets that died.

Dung said signs of the disease in Vietnam were similar to those in China, like high fever. Animals which fell ill also included adult pigs, which were normally not susceptible.

The epidemic has rattled Cambodia, which banned the import of pigs and pork from neighbouring Vietnam, Laos and Thailand.

The PRRS virus was first recognised in the United States in the mid-1980s and the disease costs the U.S. swine industry some $600 million each year.

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