Japanese encephalitis (JE) virus causes serious brain inflammation in people and fertility problems in pigs. Mosquitoes were previously the only known transmission route. However, it has now been shown that the virus can also be spread from pig to pig by direct contact, and this could enable it to circulate in pigs during the mosquito-free winter season. The JE virus is the chief cause of serious encephalitis in people in Asia. The virus is found in large parts of Southeast Asia and is now also widespread in India. It circulates between birds and mosquitoes and between pigs and mosquitoes, and is passed to humans through mosquito bites. In children, in particular, infection can lead to acute encephalitis and permanent impairment or even death. In pigs, the main effects of the virus, alongside fever and encephalitis, are fertility problems. The virus is closely related to the West Nile, Zika, and dengue viruses. All these are transmitted by mosquitoes and are flaviviruses that can cause serious illness in humans and animals. A team of researchers, from the Institute of Virology and Immunology and the University Bern at the Vetsuisse Faculty in Switzerland, and led by Dr. Meret Ricklin and Professor Artur Summerfield, have now shown that JE viruses can also be passed directly from pig to pig. The study was published on February 23, 2016 in Nature Communications. The article is titled “Vector-Free Transmission and Persistence of Japanese Encephalitis Virus in Pigs.” Until now, there had been no explanation for how the JE virus could survive over winter in regions such as the northern Japanese island of Hokkaido, and cause new outbreaks the following year. Outbreaks in some cases occurred on the same farms as in the previous year, despite the fact that no infected mosquitoes could be found in the area.
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