JEV threat to U.S. swine industry prompts continued research

U.S. favorable for the introduction of Japanese encephalitis, a zoonotic, emerging disease transmitted primarily by Culex mosquitoes infected with the virus.

August 2, 2023

5 Min Read
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The potential for Japanese encephalitis virus transmission and spread in the United States is the focus of a new investigation led by Natalia Cernicchiaro, 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 and the Foreign Arthropod-Borne Animal Diseases Research Unit, the team of researchers commenced the multi-year grant on Aug. 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 United States may spatiotemporally spread.

The United States represents an area favorable for the introduction of Japanese encephalitis, a zoonotic, emerging disease transmitted primarily by Culex mosquitoes infected with the virus. Previous incursions of other mosquito-borne flaviviruses in the United States include West Nile virus and Zika virus. Knowing the availability of competent insect vectors, susceptible avian and porcine hosts, and environmental conditions similar to those in epidemic countries creates concern in the U.S. pork industry as well as with public health officials as JEV is a mosquito disease capable of affecting humans as well as pigs.

Entities concerned about the potential of a JEV incursion in the United States include the Swine Health Information Center which has funded several projects designed to further strengthen U.S. swine industry preparedness as well as inform response efforts, should they be needed. Some of SHIC's efforts include the implementation of a systematic literature review intended to increase understanding of the virus's biology, components and dynamics of transmission, and environmental factors necessary for incursion and establishment. In addition, the same team at Kansas State University conducting the review is re-assessing pathways of JEV introduction into the United States via a risk assessment with funding provided by SHIC.

In October 2022, SHIC led efforts to hold the JEV symposium, "Emerging Global Threat to Humans and Livestock." The symposium, organized by the Center for the Ecology of Infectious Diseases and the Global Infectious Disease Intelligence Consortium at the University of Georgia, included presentations from several speakers on the early 2022 outbreak of JEV genotype IV in Australia along with response plans to support the North American pork industry. Additional information on the symposium can be found here.

The recent incursion of a new JEV genotype into areas previously free from disease, as observed in Australia with the invasion and expansion of JEV in eastern and southeastern states, warrants the need for a close investigation of this disease and its potential for incursion and establishment in the United States. Given the presence of immunologically naïve human and pig populations, a JEV incursion into the United States, followed by transmission and establishment, could lead to unprecedented disease outbreaks characterized by clinical disease in humans and in pigs, and economic losses.

Over the last 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 United States.

"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," said Cernicchiaro. "As we keep refining our understanding of JEV emergence in the U.S., 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."

In a unique collaboration, Drake is building a JEV infectious disease spatial interaction model to explain how this virus is expected to spread after potential introduction into the United States. Where a domestic outbreak begins and how quickly JEV spreads through both human populations and the U.S. pork industry are questions Drake's research will help address.

Drake's goal is to understand and predict JEV's movement across the United States over weeks or months after a potential introduction. 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.

"We know that the first human case and death from the 2022 outbreak actually occurred in February 2021 on the Tiwi Islands north of Darwin," Drake said. "The Tiwi Islands are about 700 km west of the Cape York Peninsula where previous JEV cases were reported. 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."

Modeling JEV is a unique opportunity for Drake.

"I have been very interested in modeling infectious diseases that are transmitted by mosquitoes that impact people and livestock," he said. "JEV is just one of several important diseases that affect farmed pigs, and considering the size of the U.S. pork industry, I am happy to help industry learn how our models can be used to develop contingency plans in the event of an outbreak. I am grateful to both Natalia and USDA Agricultural Research Service for their collaboration and funding to research and build a JEV model."

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