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Most emerging infections come from the transmission of viruses from animals to humans but aren’t capable of sustained human-to-human transmission, which is necessary to cause an epidemic. With the continuing increase of people living in urban areas, the frequency at which pathogens jump from animal to human hosts is expected to rise.
The research team, from the University of Sydney, arranged and analyzed a database of 203 viruses. They used statistical models to identify and quantify the biological factors of viruses that best predict which viruses are most likely to sustain human-to-human transmission. The data showed the viruses with the highest likelihood of being transmissible among humans were chronic, non-segmented, non-vector-borne, non-developed, and had a low host mortality rate.
"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 lead author Jemma Geoghegan. A good example of this is a polyomavirus, Geoghegan said. Polyomaviruses infect humans, but 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,” Geoghegan said.
The identified biological factors could be used to predict which viruses are more likely to cause epidemics, allowing public health officials to take measures to avert and contain these outbreaks.
Still, the study does not guarantee that epidemics won’t catch us by surprise in the future.
The research was published on March 21, 2016, in the Proceedings of the National Academy of Sciences.
Sources: The University of Sydney via phys.org