Synthesizing evidence and identifying knowledge gaps in the role of swine in Japanese encephalitis virus transmission: a rapid systematic review of the literature

Authors: HORTON, VANESSA - Kansas State University; HANTHORN, CHRISTY - Kansas State University; DIXON, ANDREA - Kansas State University; EDACHE, STEPHEN - Kansas State University; THACKRAH, ASHLEY - Kansas State University; Mitzel, Dana; NORONHA, LEELA - US Department Of Health & Human Services; Cohnstaedt, Lee; BROWN, V.R. - Animal And Plant Health Inspection Service (APHIS); Mire, Chad; CERNICCHIARO, NATALIA - Kansas State University

Submitted to: Frontiers in Sustainable Food Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2024
Publication Date: 11/27/2024
Citation: Horton, V., Hanthorn, C.J., Dixon, A.L., Edache, S., Thackrah, A.M., Mitzel, D.N., Noronha, L., Cohnstaedt, L.W., Brown, V., Mire, C.E., Cernicchiaro, N. 2024. Synthesizing evidence and identifying knowledge gaps in the role of swine in Japanese encephalitis virus transmission: a rapid systematic review of the literature. Frontiers in Sustainable Food Systems. 8. Article 1455455. https://doi.org/10.3389/fsufs.2024.1455455.
DOI: https://doi.org/10.3389/fsufs.2024.1455455

Interpretive Summary: The United States is susceptible to the introduction of the Japanese encephalitis virus (JEV) because of travel and trade from countries that have human cases in South and Southeastern Asia and the two environmental and weather similarities between the two regions. While these activities will introduce the virus to suitable climates in the United States, establishment or virus transmission in the US will depend on mosquito, bird, and pig species capable of maintaining and transmitting the virus. Facilitating the virus transmission and late detection of an introduction or establishment of the virus is the lack of JEV surveillance in mosquitoes, birds, or pigs. Pigs are considered the primary amplifying host and further research is needed to identify their role in JEV transmission to provide guidance to decision-makers so they are handled appropriately during emergency responses. This project gathered and synthesized the scientific literature to identify knowledge gaps and potential areas amenable for future research. A total of 3,638 records were initially identified. Data were extracted from 227 records. Transmission of JEV occurs primarily via infected mosquitoes; however, some evidence of direct transmission between pigs was reported. In swine, breed or sex had no association with JEV transmission. Sound biosecurity practices and vector control are recommended as preventive measures against introduction and spread of JEV in swine farms. Although there is no JEV vaccine licensed for pigs in the U.S., live attenuated vaccines were reported to elicit superior efficacy compared to inactivated vaccines. Summarizing the current understanding of JEV infection will guide researchers, stakeholders, and policymakers to prioritize research efforts and develop effective countermeasures. This is particularly crucial prior to an outbreak in the U.S., where preventative measures will minimize the spread of the virus, safeguard both human and animal populations, and ensure the long-term sustainability of the swine production sector.

Technical Abstract: The United States (U.S.) is considered a susceptible region with great potential for the introduction of the Japanese encephalitis virus (JEV) given the presence of competent mosquito vector species, susceptible maintenance avian hosts, large populations of susceptible domestic and feral swine, intensive travel and trade activities to and from JEV-endemic countries, similar climatic and environmental conditions to epidemic countries, and no active JEV surveillance in place. As pigs are considered JEV’s primary amplifying host, comprehensively reviewing the available body of evidence, and respective knowledge gaps, pertaining to the role of swine in JEV transmission can provide valuable guidance to decision-makers. Our objectives were to synthesize scientific literature on the role of domestic and feral swine in the transmission of JEV via a rapid systematic review and identify knowledge gaps to determine potential areas amenable for future research. A total of 3,638 records were initially identified. Data were extracted from 227 reports. Transmission of JEV occurs primarily via infected mosquitoes; however, some evidence of direct oronasal transmission between pigs has been reported. Despite pigs exhibiting a short-lived viremia, JEV has been demonstrated to persist longer in their tonsils. In sows, JEV infection may cause reproductive disorders, and although maternal antibodies can confer protection for several months under field conditions, naïve piglets can exhibit neurologic signs which may progress to wasting disease. Studies evaluating breed or sex reported no association with JEV seropositivity. Application of biosecurity practices and vector control are recommended as preventive measures against introduction and spread of JEV in swine farms. Although there is no JEV vaccine licensed for pigs in the U.S., live attenuated vaccines were reported to elicit superior immunogenicity compared to inactivated vaccines used in endemic countries. Summarizing the current understanding of JEV infection in swine can guide researchers, stakeholders, and policymakers in prioritizing research efforts and developing effective countermeasures. This is particularly crucial in the event of an outbreak in the U.S., where preemptive measures can help minimize the spread of the virus, safeguard both human and animal populations, and ensure the long-term sustainability of the swine production sector.