With changes in land use and increased urbanization, the frequency with which pathogens jump species barriers to emerge in new hosts is expected to rise. Knowing which viruses may be more likely to become transmissible among humans, as opposed to only generating dead-end spillover infections, would be of considerable benefit to pandemic planning.

To address this issue, a team from the University of Sydney’s Charles Perkins Centre compiled and analyzed a database of 203 human viruses and used statistical models to identify biological factors that predict which viruses are most likely to successfully emerge in human populations.

Their findings were published this week in the Proceedings of the National Academy of Sciences.

“The probability of human-to-human transmission was increased by low host mortality and the ability to survive in the host for an extended time, both of which allow a virus more time to spread,” said the paper’s lead author, Dr. Jemma Geoghegan. “A good example of this is polyomaviruses – a family of viruses that infect humans but which rarely cause symptoms or illness.

“In contrast, viruses that possess a particular structure called an ‘envelope’ seem less able to emerge in humans because they are more easily degradable and not environmentally stable. In the same way, viruses that are transmitted by insect vectors, such as mosquitoes, are also less likely to spread among humans. So, although diseases like dengue and Zika have received a great deal of attention, they are very much the exception rather than the rule,” she added.

According to the authors, these biological factors could be used to predict which viruses are more likely to cause epidemics, enabling public health officials to take appropriate measures to prevent and contain these outbreaks.