单项选择题

Thailand confirmed three new human bird flu cases Thursday as health officials warned it could take two years to conquer Asia’s outbreak. Meanwhile, the World Health Organization said the latest tests show no sign of a killer hybrid virus that could easily pass between people.
Tests on a cluster of bird flu cases in a Vietnamese family showed there was no mixing of genes between the bird flu strain and human flu, according to WHO.
In the United States, a strain of bird flu was found at four live chicken markets in northern New Jersey, just days after outbreaks at two farms in Delaware led to the destruction of thousands of birds.
WHO has said the best way to control the spread of the disease is by culling the birds. In Asia, tens of millions of chickens have been killed by infections or slaughtered in containment efforts as bird flu spread, jumping to people in Vietnam and Thai-land.
The human death toll stood at 19 on Thursday.
While two of the three people labeled as new cases in Thailand have recovered, the third, a 13-year-old boy, was in intensive care in northeastern Chaiyaphum province, Thai officials said.
Fears of an outbreak prompted Singapore, believed free of bird flu, to announce plans to euthanize 5,000 healthy chickens in a drill to prepare for any possible infection.
Ten governments in the region have dealt with the disease over the past couple of months, with China boosting its culling efforts as reports of infections there increased.
Beijing said Thursday it was mobilizing 16,000 workers for anti-bird flu efforts in a province bordering Vietnam where China’s first bird flu case of the season was confirmed in late January. Among their tasks is to try to pinpoint the source of the first infection.
Destroying infected fowl is the best way to contain the outbreak, according to WHO.
Thai officials have said slaughters of more than 26 million chickens have brought the disease largely under control there, while Vietnam has said its outbreak is easing. In Pakistan, U. N. officials said the disease has been contained. But the U. N. Food and Agriculture Organization said it would take much longer to bring the region’s outbreak under control.
"I would have thought that we’d be looking at a period of six months...but it could be as long as two years," FAO animal health officer Peter Roeder said in Geneva. In New Jersey, state veterinarian Nancy Halpern said the markets likely got the virus from one of their many farms and distributors. New Jersey has about 35 live chicken markets.
Which one of the following countries has not been infected with human bird flu