DEPARTMENT OF AGRICULTURE

Bird flu is highly lethal to some animals, but not to others. Scientists want to know why

​In the United States, animal outbreaks have been reported at dozens of dairy cow farms and more than 1,000 poultry flocks, according to the U.S. Department of Agriculture. Four human infections have been reported among the hundreds of thousands of people who work at U.S. poultry and dairy farms, though that may be an undercount.