Research Ties Flu Pandemic to U.S. Swine

By analyzing viral genes from lung tissue preserved for 79 years, researchers have determined that the 1918 flu epidemic that killed 20 million people worldwide was caused by a virus from American pigs.

In a study published Friday in the journal Science, researchers at the Armed Forces Institute of Pathology said they found the virus traces in tissue taken from the autopsy of an Army private who died of the flu in 1918. He was one of about 700,000 people killed by the epidemic in the United States.

Dr. Jeffery K. Taubenberger, leader of the research team, said the genetic pattern of the virus shows that although it’s closely related to “swine” flu, the 1918 influenza virus is unlike any other flu bug.

“This is the first time that anyone has gotten a look at this virus, which killed millions of people in one year, making it the worst infectious disease episode ever,” he said. “It does not match any virus that has been found since.”

Although the disease that caused the worldwide epidemic was called “Spanish flu,” the virus apparently was a mutation that evolved in American pigs and was spread by U.S. troops mobilized for World War I, he added.

Using specimens collected by Army doctors in 1918 Taubenberger’s team partially sequenced the genes for hemagglutinin and neuraminidase, two key proteins in flu virus, in a virus sample taken from the private’s lung tissue.

“The hemagglutinin gene matches closest to swine influenza viruses, showing that this virus came into humans from pigs,” Taubenberger said.