Studies suggest the U.S. represents an area favorable for the introduction of Japanese encephalitis virus (JEV). JEV, a zoonotic, emerging disease transmitted primarily by Culex mosquitoes infected with the virus. Past mosquito-borne flaviviruses in the U.S. such as West Nile virus and Zika virus illustrate the challenges a virus like JEV that is capable of affecting humans and pigs could pose in the U.S.
The potential for JEV transmission and spread in the U.S. is the topic of new investigation led by Natalia Cernicchiaro of Kansas State University College of Veterinary Medicine and John Drake, Director of the Center for the Ecology of Infectious Diseases at the University of Georgia. With funding from and in collaboration with researchers from the USDA, National Bio and Agro-Defense Facility, Foreign Arthropod-Borne Animal Diseases Research Unit, the team of researchers began the multi-year grant on August 1.
“Researchers will model transmission dynamics in the case of a JEV incursion, integrating climatic and regional factors, under specific local conditions, considering vectored and vector-free transmission among swine and other animal hosts. Additionally, a JEV spatial interaction model will be built to estimate, predict, and forecast how a JEV outbreak in the US may spatiotemporally spread,” the Swine Health Information Center (SHIC) reports.
This project follows the implementation of a systematic literature review and a reassessment of the pathways of JEV introduction into the U.S. via a risk assessment with funding provided by SHIC.
Why Now?
The recent incursion of a new JEV genotype into areas previously free from disease prompted the close investigation of this disease. The early 2022 outbreak of JEV genotype IV in Australia was a wake-up call, experts say.
“Given the presence of immunologically naïve human and pig populations, a JEV incursion into the US, followed by transmission and establishment, could lead to unprecedented disease outbreaks characterized by clinical disease in humans and in pigs, and economic losses,” SHIC reports.
Over the past nine years, Cernicchiaro’s team has investigated vector and host competence, as flavivirus-mosquito interactions are central to the epidemiology of JEV and its epidemic potential, as well as the risk of JEV emergence in the U.S.
“In 2018 our team assessed all potential pathways of JEV introduction via risk models. Entry of adult mosquitoes via aircraft of adult mosquitoes into the west and east coasts was deemed the most likely pathway of incursion,” Cernicchiaro said in a SHIC release. “As we keep refining our understanding of JEV emergence in the US, our team will next work on elucidating factors responsible for transmission through development of models that can capture key features of the disease process and the dynamics of epidemics.”
Drake is building a JEV infectious disease spatial interaction model to explain how this virus is expected to spread after potential introduction into the U.S. Where a domestic outbreak begins and how quickly JEV spreads through both human populations and the U.S. pork industry are key questions Drake will try to answer, SHIC reports.
“One of the expected outcomes of this project is to help the public health authorities and pork industry veterinarians understand how a JEV epidemic might be thwarted. The 2022 JEV outbreak in Australia that rapidly appeared in commercial swine operations across the eastern half of the country resulted in their government declaring a Communicable Disease Incidence of National Significance, further spurring to this project,” SHIC reports.
The first human case of JEV and death from the 2022 outbreak actually occurred in February 2021 on the Tiwi Islands north of Darwin, Drake explained.
“The Tiwi Islands are about 700 km west of the Cape York Peninsula where previous JEV cases were reported,” Drake said. “The virus that spread from the Tiwi Islands into the interior of the country, including South Australia and Victoria, is genetically similar to a JEV virus isolated in Bali, Indonesia in 2017. JEV viruses that have been circulating on the Cape York Peninsula originated in Papua New Guinea, and they did not contribute to the 2022 outbreak.”
Drake said he is looking forward to learning how models can be used to develop contingency plans in the event of an outbreak.
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