China's chief veterinarian says a pig virus outbreak that has killed tens of thousands of pigs is under control. But as VOA's Heda Bayron reports from Hong Kong, doubts remain over the extent and nature of the outbreak as China has yet to share samples with international laboratories.

China has been criticized for not sharing samples of a virus that it says infected 175,000 pigs and killed tens of thousands of those, across most of the country.

China says the disease is now under control after pigs were vaccinated. But without samples, international experts wonder whether the virus is really what China says it is. China identifies it as blue ear disease or porcine reproductive and respiratory syndrome or PRRS, which is read by scientists as "Pers".

Some experts are alarmed at the large number of pig deaths in China, saying it is unusually high.

Juan Lubroth, senior officer of infectious diseases at the Food and Agriculture Organization says Chinese scientists told the U.N. agency the virus has changed.

"What they have alerted us to is that this particular virus seems to be hotter or more virulent than what was previously described in North America, Europe or elsewhere," he said. "So there has been some changes in the virus that perhaps make it a bit more lethal. This needs to be studied further and we have to see whether it's acting alone or acting in synergy with some other pathogens."

This is why, Lubroth says, an independent confirmation from a laboratory specializing on the PRRS virus is needed.

Jia Youling, China's chief vet, said Monday no such request has been made.

Jia says he does not know where to send the samples because he does not know who needs them.

He added that China does not need international help in detection because Chinese experts fully understand the structure of the virus.

PRRS causes high fever, diarrhea and rashes in pigs, turning their ears blue, but is not infectious to humans.

Chinese scientists say that in the past, fatal cases from PRRS mostly involved young pigs. But now it is infecting many adult pigs, the disease duration is shorter and it is more contagious. They conclude that environmental factors such as temperature and high humidity, and secondary bacterial infections, may be sparking mutation.

The Chinese government has been sharply criticized in the past for not promptly sharing information about infectious disease outbreaks.

When the highly infectious Severe Acute Respiratory Syndrome or SARS appeared in 2003, it jumped from animals to humans. It spread quickly and killed many people all over the world before China admitted being the source of the outbreak.

The PRRS outbreak this year has caused economic losses to China's pig farmers and the pig deaths are believed to be helping drive pork prices up.

Veterinary experts are also investigating a blue ear outbreak in Vietnam, raising concerns that the virus may have spread beyond China's borders.

Neighboring Cambodia has banned imports of live pigs because of the outbreaks.