Infecting tens of thousands of people, and claiming the lives of almost half of those, the outbreak of Ebola a few years back was the worst ever experienced. But it now seems that the vast majority of those who were infected with the disease contracted it from a tiny proportion of people.
A recent study, published in the Proceedings of the National Academy of Sciences, has found that 61 percent of all the recorded cases of Ebola that occurred during the 2014-2015 outbreak were likely spread by just 3 percent of those infected. What’s more, there was a distinct pattern in these “superspreaders”, which were more likely to be either under the age of 14 or over the age of 45.
By looking at where and when new cases emerged, the researchers were able to build up a precise pattern of how the disease spread through the region to such a fine resolution that they could even calculate how many people each individual infected person spread the virus to. While most people with Ebola only had a small window in which they were infectious, there was a smaller group who were infectious for much longer periods of time.
“The recent West African outbreak was on an unprecedented scale and many cases, especially those occurring out in the community, appear to have arisen from a surprisingly small number of infected individuals,” explained Professor Jonathan Ball to BBC News. “Whether this was due to biological or social factors is unclear, and these will be important questions to address if we are to understand how Ebola virus super-spread occurs.”
The researchers suggest that those who were the so-called “superspreaders” were not necessarily more infectious than the others. Rather, it may be that the children and older members of the communities were more likely to come into contact with a larger number of people, as friends and family members rallied around to care for them. This would have vastly increased the number of people to which the disease could then be spread, far more so than a single individual living in a house on their own.
By understanding precisely how the virus spread, the researchers hope to build up a much more effective management system for if, or when, it remerges. It would mean that they could then target the superspreaders, and hopefully dramatically slash the number of infections.