Global disease monitoring by the Swine Health Information Center has identified Japanese encephalitis virus (JEV) as an emerging disease to watch. This zoonotic disease is transmitted through the bite of Culex mosquitoes infected with the virus that’s primarily maintained in endemic Southeast Asia and Pacific Island nations. However, outbreaks in Australia have alerted the entire world to keep an eye on this deadly virus.
“The U.S. is currently negative for this mosquito-borne virus which has waterbirds as a natural reservoir host but can infect pigs, humans, and horses,” Megan Niederwerder, executive director of the Swine Health Information Center, said at the American Association of Swine Veterinarians Annual Meeting on March 2. “However, the U.S. represents a geographic region susceptible to the introduction of JEV.”
JEV affects breeding swine herds, causing reproductive failure, delayed farrowing, stillbirths, mummified fetuses, abortions and weak piglets.
“In February 2025, JEV re-emerged in Australia marking the first detections of the virus in Australian commercial swine since July 2022 after no cases were detected in piggeries during 2023 or 2024,” Niederwerder says.
This recent incursion and re-emergence of a new JEV genotype into areas previously free from disease warrants the need for close investigations of this disease and its potential for incursion and establishment in the U.S., she explains.
“One of the lessons learned from the Australian experience with JEV in 2022 was a report that increased mummified fetuses was the most common clinical sign on sow farms and the only clinical sign reported by 100% of veterinarians interviewed about their swine observations during the outbreak,” Niederwerder says. “This is important as it gives U.S. veterinarians and producers firsthand accounts of what they should be watching for on farms for early detection of a potential JEV incursion.”
JEV: What You Need to Know
Biosecurity practices focused on mosquito control are often the most effective way to prevent JEV as it is transmitted through the bite of an infected mosquito.
“Knowing the availability of competent insect vectors, susceptible avian and porcine hosts, and similar environmental conditions in the U.S. compared to JEV endemic countries creates concern for the U.S. pork industry as well as with public health officials,” she says.
The U.S. south was identified as having the highest risk of JEV incursion and impact, according to a SHIC-funded study.
“Research priorities for JEV are designed to further strengthen U.S. swine industry preparedness as well as inform response efforts, should JEV be introduced into the country,” she says. “Understanding the potential impacts of JEV on pork production in the U.S. is critical to protecting the health of the U.S. swine herd as well as mitigating the risk of this emerging disease”.
How JEV Could Impact the U.S. Swine Herd
The potential economic losses to the U.S. pork industry if a JEV outbreak were to occur in this country is estimated to be between $306 to $612 million in a single year, she says.
SHIC partnered with the Foundation for Food & Agriculture Research (FFAR) to develop and fund a $1.3-Million JEV Research Program. The goals of the Program are to enhance U.S. prevention, preparedness, mitigation and response capabilities for JEV. Learn more here.
Critical research investments are necessary to prevent JEV incursion, Niederwerder adds. Research will continue into how to ensure rapid detection of JEV if introduced, inform stakeholder response, mitigate production losses on sow farms, identify effective control measures, and develop clear messaging to consumers on the safety of pork.
