It is unclear if this form of sharing the disease also occurs outside of the lab. “It’s probably not the dominant mode of transmission,” Juliet Pulliam, a virologist at the University of Florida in Gainesville who was not involved in the research, told Science. But pig-to-pig transmission could explain how the virus sometimes persists year-round, even in the winter when mosquito populations decline.
“If you look in the older literature, you find a lot of speculation,” study coauthor Artur Summerfield, a virologist at the Institute of Virology and Immunology in Bern, Switzerland, told Science. “But nobody was able to demonstrate where [the virus] was sleeping in the winter.”
This is the first study to demonstrate mosquito-free spread of the Japanese encephalitis virus, but previous research has shown that the closely related West Nile virus can be transmitted directly from bird to bird. And recent reports have suggested that the mosquito-borne Zika virus may be transmitted sexually between humans. “As we’re getting better at looking at things, people are noticing these weird patterns,” Pulliam told Science. “We’re starting to pick up on things that maybe we wouldn’t have picked up on before.”