A relatively new hybrid form of cholera, a disease underscored by recent deadly outbreaks in Zimbabwe and Haiti, may be more dangerous than past strains, according to researchers at Massachusetts General Hospital and Harvard University.

Edward T. Ryan, an associate professor at the Harvard Medical School and the Harvard School of Public Health, said that cholera has undergone two major mutations in the last twenty or so years. The first, in the early 1990s, involved a change in the bacteria’s “coat,” which allowed it to infect those previously thought to be immune to the disease.

The second mutation has made the disease more deadly, according to Ryan. In an editorial published in Jan. 25 in the journal “PLoS Neglected Tropical Diseases,” Ryan wrote that the cholera caused by the new hybrid strain may be more severe, which “may explain why we are seeing case fatality rates of 1 to 5 percent in recent outbreaks as opposed to under 1 percent historically accepted as the goal for response teams.”

For the past five years, researchers at Harvard University’s Edward T. Ryan Laboratory have been studying the immune responses of humans infected with the cholera bacterium, Vibrio cholerae. According to the Ryan Laboratory’s website, the researchers hope to identify the “mediators of protection against cholera” to better inform the development of new vaccines and methods of prevention.

“Our work focuses on the immune response to a new cholera vaccine,” said Ryan, who runs the laboratory. “We want to identify protection factors to help develop knowledge and find a vaccine.”

“The current usable vaccines provide a protective immune response that lasts just six months to two years,” said Richelle C. Charles, an instructor at Massachusetts General Hospital and a researcher at the Ryan Laboratory. Charles said that a goal of the research would be to extend the period of time for which people remain immunized.

Charles recently spent three weeks in Haiti providing clinical help to Haitians affected by the ongoing cholera pandemic. During that time, she also collected samples for research.

The Ryan Laboratory is collaborating with four other Harvard professors and the International Centre for Diarrhoeal Disease Research in Dhaka, Bangladesh. Researchers at the center famously discovered oral rehydration therapy, a treatment for cholera and diarrhea, which Ryan said has saved over 40 million lives since its discovery in 1969.

The media has extensively covered the ongoing cholera outbreaks in Haiti and Zimbabwe. Currently, the world is experiencing the seventh cholera pandemic since the 1820s. The pandemic, which began in 1961 in Indonesia and has since spread across Asia and Africa, among other places, is now in its 50th year.

“It catches the attention of the media for a couple major outbreaks, but we’re concerned with the long-term [effects],” Ryan said.

—Staff writer Benjamin M. Scuderi can be reached at bscuderi@college.harvard.edu.