Super-Spreaders and Genetic Susceptibility: Study Looks to Pull the Curtain Back on Colds and Flu

World-famous for its dinosaurs, the American Museum of Natural History is offering visitors a chance to take part in an experiment with decidedly human subjects: the microbiome. Since mid-May, hundreds have had their nose, tongue, and hands swabbed so scientists can better understand the diversity of healthy bacteria and viruses living in our bodies, an idea explored in the exhibit The Secret World Inside You.

Led by Jeffrey Shaman, Mailman associate professor of Environmental Health Sciences, the experiment at the museum is related to a larger study funded by the U.S. Department of Defense that will collect and analyze samples from local high schools and a pediatric emergency department to shed light on some less friendly microbes—respiratory viruses—and the varying ways our immune systems respond to them.

“While we all suffer from colds and flu, we still know very little about their transmission dynamics,” says Shaman, known for his work developing computer models to forecast outbreaks of influenza and Ebola. Today’s public health system has good information on severe respiratory infections based on hospital admissions; far less is known about how many people are infected with mild illness or without any symptoms at all—and what role these semi-healthy people play in spreading the virus to others whose immune system may react more strongly.

“A person may be asymptomatically infected but may shed so little [virus] as to not participate in the chain of transmission,” he says. “Without coughing and sneezing, there may not be a viral load sufficient to make someone else sick. On the other hand, it may be that there are asymptomatic ‘super-spreaders’ who are very contagious but without symptoms.”

If someone with the flu typically infects two other people, a super-spreader might infect many more. School-age children may act as super-spreaders since they interact with many other children in close quarters, often without washing their hands. And since they’ve been exposed to far fewer viruses than adults, children have fewer antibodies, and are therefore more likely to get sick.

Once a week during cold and flu season, the researchers will take samples from study participants irrespective of whether they feel any symptoms. Using genetic testing, they will determine if someone is infected with one of the suspect viruses and to what degree. Then they will map this information with the individual’s genetic makeup.

Could genes play a role in whether a cold puts us home in bed or goes unnoticed? Are some immune systems prone to overreact? “We all know people with a propensity to get sick more often,” says Shaman. “Is this due to a genetic difference that makes their innate immune system more reactive so that they feel really sick? Some people may be at risk for dying from the severity of their immune response to infection. Understanding why that takes place is very important.”

Ultimately, Shaman hopes the information gleaned from the study will help the development of the next-generation computer models for understanding and forecasting how infections like flu spread in a population. This information will help public health officials and the public at large to take the necessary precautions.

It’s a goal that the study’s funders, the DOD’s Defense Advanced Research Projects Agency (DARPA), has made a priority. “The military has always been interested in infectious disease, and for good reason,” Shaman says. “In the history of the U.S. military, more people have died from infectious disease than combat.”