It’s easy to develop a paranoia of social situations at this time of year. It seems like every friend, relative, coworker, and stranger on the bus is a potential carrier of the cold and flu viruses that spread during the winter months. Not everyone poses an equal threat, however. It’s estimated that roughly 20% of the population are so-called “super-spreaders” who transmit 80% of infectious disease cases in that population. It’s not entirely clear why this is true, however, or how much of this effect is due to biological or behavioral factors.
A recent study investigated the spread of salmonella infection in mice and discovered something interesting about the immune systems of the super-spreaders in the bunch. It wasn’t that their immune systems were necessarily better or worse at fighting the salmonella, just more tolerant of its potential effects. Identifying the mechanism behind this tolerance might help explain the existence of extreme super-spreaders like Typhoid Mary.
It’s not always true, though, that super-spreaders don’t feel the effects of their illnesses. A 2003 CDC report details the harrowing cases of five super-spreaders, hospitalized in Singapore during the beginning of the SARS epidemic. The magnitude of contagion described in the report is shocking—each super-spreader could be directly or indirectly linked to between 20 and 60 SARS infections, with one potentially infecting over 20 healthcare workers who merely walked down a corridor the patient had used.
Super-spreaders don’t necessarily have to be a single individual, either. This 2006 article explains how a relatively uncommon bird species, the American robin, was disproportionately responsible for the spread of West Nile virus to mosquitoes in DC and Maryland.
Further research into super-spreaders will hopefully decrease our sickness, along with our healthy paranoia of the new sniffles and sneezes we hear around us during wintertime. It goes without saying, though, that until the mystery of the super-spreader is solved, you should absolutely get a flu shot.
Morbidity and Mortality Weekly Report, Vol. 52, No. 18 (May 9, 2003), pp. 405-408, 410-411
Centers for Disease Control & Prevention (CDC)
Proceedings: Biological Sciences, Vol. 273, No. 1599 (Sep. 22, 2006), pp. 2327-2333
The Royal Society