MISSOULA – When biologists track how a virus moves among animals, they normally map the path of the disease within just one species. UM Professor Angie Luis realized this wouldn’t work for studying viruses in bats. Viruses pass easily between species of this flying mammal, so she wanted a method to study whole communities of bats.
In a new study published Aug. 24 in Ecology Letters, Luis and her colleagues used a network approach to see how bat communities share viruses and compare those findings with rodent communities. The paper is titled “Network analysis of host-virus communities in bats and rodents reveals determinants of cross-species transmission.”
After sifting through the scientific literature from the past 70 years and compiling data on 339 host species connected by 282 viruses, Luis’ team found the rodent virus-sharing network is only about 60 percent as connected as the bat network, meaning viruses seem to pass more easily between bat species than between rodent species.
Some of bats’ unique characteristics may help facilitate this transmission of viruses between species. Some bat species can have massive colony sizes in the millions and some of these roosts can house a diverse array of bat species. This is the perfect opportunity for viruses to spread between individuals and between species. Luis and her colleagues found bats with larger colonies were more likely to be more connected in the network, making it easier for them to share viruses with more species.
Bats are the only flying mammal, and the study showed bats that migrate regionally are important in the network. These “betweenness” bats might not host or share the most, but they connect different communities of bats to help viruses spread between different groups.
Luis’ study is the first analysis to identify communities of pathogen sharing on a global scale. This is important for protecting human health, as both bats and rodents carry a number of viruses that can infect humans, including ebola and SARS. Bats are more likely to share those viruses with their cross-species cousins.
Bats are the second-most diverse mammalian order (after rodents) with 1,100 species. Differences between species are created by size, diet, whether the bat echolocates or not, and more. These differences aren’t such a big deal when it comes to sharing a virus. That sharing depends mostly on three things: where the species overlap in distribution, the size of the colony (gregariousness), and migration habits.
“One thing that struck me early on in this study is just how many times viruses have jumped between species in both bats and rodents,” Luis said. “The opportunity for contact between two species appears more important than how closely related those species are, at least within taxonomic order. Perhaps the ‘species barrier’ is less of a barrier than we think.”