Researchers have developed a model that predicts which viruses can jump from animals to humans can also be transmitted from person to person – and therefore may be a source of human disease.
Studies published recently on PLOS One, identifying several viruses that have not been known to spread among humans but may have that potential, suggesting possible targets for future disease surveillance and research efforts.
"When we get new pathogens that we see as new human diseases, most of the time they come from pathogens previously circulating in animals," said John Drake, Professor of Ecological Research and Director of the Center for Ecological Infectious Diseases at the University of Georgia. "As ecologists, it makes us think that there must be something about the way parasites and pathogens interact with their hosts or the environment that bestows tendencies on this process."
To understand this interaction, Drake and his team compiled the most comprehensive list of viruses known to infect humans and the biological characteristics of the virus.
"We are looking to identify viral features related to transmissibility between humans," said lead author Joseph Walker, a key statistic that works under the direction of Drake through the UGA Center for Undergraduate Research Opportunities.
The team identified some of the most common traits among viruses on their list that were known to spread among humans. This includes the ability to infect non-human primates such as monkeys and apes, lack of lipid envelope folds around viruses, and the presence of viruses in the human liver, central nervous system or respiratory tract. These characteristics – characteristics that show the ability of the virus to survive in different environments and evolve – accurately predict 84 percent of viruses known to spread from human to human.
The next step is to analyze viruses that are not known to spread between humans and determine how likely it is that the virus can be transmitted based on its properties. They found 47 viruses that ranked higher than the virus that was most unlikely to be known to be transmitted. Of these, the most likely spread among people was Carnivore amdoparvovirus 1, Hendra virus, Cardiovirus A, Rosavirus A, HTLV-3, HTLV-4 and Simian Foamy virus.
The researchers warn that although the model predicts human-to-human transmission with high accuracy, it does not lose some viruses that are known to spread among people. These tend to belong to five families that contain many species. And because this study considers viruses at the species level, it cannot explain the differences in human transmissibility between viral subtypes. They recommend that future research focus on understanding transmissibility on this finer scale.
The ability to predict which viruses are capable of spreading among humans, and therefore potentially causing human epidemics, has practical implications.
"Public health workers can use our model as a tool to prioritize disease surveillance and inform their responses to emerging pathogens," said co-author Barbara Han of the Cary Institute of Ecosystem Studies. "Our data-based framework is 84 percent accurate in identifying virus species with potential human-to-human transmission."