A dog is suspected to be the origin of an outbreak of pneumonic plague in northwest China that has killed three people and left 10,000 under strict quarantine, state media reported.
Ziketan, a remote town in a Tibetan area of Qinghai province, has been locked down since Saturday in an effort to contain the spread of the highly virulent disease.
One patient was in critical condition and seven others were infected, most of them relatives of the first fatality, a 32-year-old herdsman, or local doctors, Xinhua news agency said.
Initial tests had shown that the herdsman's dead dog was the likely origin of the outbreak, Xinhua reported late Wednesday, quoting professor Wang Hu, director of the Qinghai disease control bureau.
Wang said it was likely that the dog died after eating a plague-infected marmot and that the man became infected while burying the dead dog. He died three days later.
"The first victim buried the dead dog without any protection. After he became infected, his relatives and neighbours were in close contact with him without taking any protective measures, leading to their infection," Wang was quoted as saying.
The World Health Organization says the bacteria which causes the plague is endemic in some rodents in the region, such as marmots.
Chinese health ministry experts quoted by Xinhua said the strict quarantine measures were proving effective and the outbreak was unlikely to spread further.
"There is no need to worry about the infection if you travel to Qinghai, not to speak of panic," professor Liang Wannian, deputy director of the ministry's emergency office, was quoted as saying.
The remote and mountainous area is sparsely populated, which is also helping to contain the outbreak.
Residents of Ziketan contacted by AFP Wednesday said some people had tried to flee but it was unclear if any had managed to breach the quarantine zone, which covers an area of 3,500 square kilometres (1,400 square miles) centred on the town.
Pneumonic plague spreads through the air, making it easier to contract than bubonic plague, which requires that a person is bitten by an infected flea.
The WHO says pneumonic plague is the most virulent but least common form of plague. The mortality rate is high and patients can die 24 hours after infection.