The phrase “swine flu” might have been new to most people’s vocabularies this spring, but… The phrase “swine flu” might have been new to most people’s vocabularies this spring, but new research shows that the virus has existed for almost 100 years.

Dr. Shanta Zimmer, an assistant professor of medicine at Pitt, and Dr. Don Burke, dean of the Graduate School of Public Health, dug through medical and veterinary literature and found that the virus traces back to a pig show held in Iowa in 1918, during the Spanish flu pandemic.

Their research, which will be published in the July 16 issue of the New England Journal of Medicine, shows that the H1N1 virus, also known as the swine flu, originated in birds and spread throughout the human and pig populations simultaneously.

Zimmer said documents describing the death of pigs at a Cedar Rapids, Iowa, pig show prove that swine there died of the flu at the same time the H1N1 virus infected humans.

From 1918 to 1957, the virus evolved differently in the pig and human populations, creating two strains with different molecular markers, Zimmer said.

The H1N1 virus is named for and characterized by the presence of two proteins, hemagglutinin and neuraminidase. The human immune system responds to the antigens present on these proteins and develops antibodies that eventually make human populations immune to a specific strain of the virus.

Zimmer said the revelations of the decades-old health records surprised her.

“Before I wrote the review,” she said, “I wouldn’t have thought that so much pig-to-human transition occurred with the H1N1 virus.”

But these isolated incidents between pigs and humans never caused public alarm, because the virus hadn’t yet evolved the capability to spread from human to human, she said.

In 1957, the human strain of H1N1 disappeared because of increased immunity in the human population and competition from a new virus, H2N2.

But H1N1 remained in the pig population and continued to infect humans sporadically, including a 1976 incident at Fort Dix, an army base in New Jersey.

Because of the close quarters of an army barracks environment, the pig virus spread through humans, resulting in 230 cases and one death. The virus didn’t spread beyond Fort Dix, but the U.S. government implemented a mass vaccination program, through which 40 million people were vaccinated.

The program failed.

The vaccine caused some people to get Guillane-Barre syndrome, a disease in which the immune system attacks the nervous system. 32 people died.

In 1977, the human strain of H1N1 mysteriously re-entered the human population. Zimmer’s findings suggest that it escaped from a laboratory in China.

Since the outbreak of the once-dormant human strain, human, pig and bird strains of H1N1 have reassorted to create the newest strain, which generated the current global pandemic that continues to spread.

The strain, originally contracted from pigs, has now evolved full capability to move from human to human.

Officials said they worry that the H1N1 strain will evolve more between flu seasons and return next spring with a deadlier virulence.

Grant money from the National Institutes of Health funded Zimmer’s review, and the review was only a small part of the vaccine research coordinated by Burke at the Graduate School of Public Health.

Burke could not be reached for comment.

“He’s interested in preventing viruses globally with vaccines,” Zimmer said. “He wants vaccines to be transmitted all over the world.”

Zimmer’s review will help people understand the history and behavior of the H1N1 virus, but she said it doesn’t directly affect the current development of a new vaccine.

“The big-picture message here is that global communities need to work together to find out when a virus might adapt to humans,” Zimmer said.

Her historical review shows that increased surveillance of animal populations might help public health officials predict when a virus is likely to spread to humans.