Revisiting the role of swine on the risk of Japanese Encephalitis Virus (JEV) transmission in the United States: a rapid systematic review of the literature

Abstract

Japanese Encephalitis (JE) is an emerging, zoonotic disease caused by the Japanese encephalitis virus (JEV), which is transmitted primarily by Culex species mosquitoes (particularly Culex tritaeniorhynchus). The JEV maintains its life cycle between mosquitoes and vertebrate hosts, primarily pigs and wading birds (Le Flohic et al., 2013). In humans, JEV infection causes inflammation of the brain (encephalitis) as well as fever, headache, respiratory distress, gastrointestinal pain, confusion, seizures, and, in some cases, death (Fischer et al., 2012; Hills et al., 2014). The global incidence of JE is uncertain. Effectiveness and quality of JE surveillance in endemic countries vary (Jayatilleke et al. 2020), as does availability of diagnostic testing throughout the world. Between 50,000 and 100,000 JE cases per year are estimated to occur in endemic countries (WHO, 2006; Campbell et al., 2011, Quan et al., 2020). Among all clinical cases, children under the age of 10 comprise the majority affected (WHO, 2006). Whereas less than 1% of the cases are accompanied by symptoms, 30% of the symptomatic cases are fatal (Campbell et al., 2011). Being untreatable and incurable, once introduced in a community, JE can lead to devastating economic and health impacts. The United States (US) is considered a susceptible region with great potential for JEV introduction. The availability of competent vectors, susceptible maintenance hosts (avian), intensive travel and trade activities to and from JEV-affected countries, areas with similar climatic and environmental conditions to countries where the virus is epidemic, and large populations of susceptible, amplifying hosts (domestic and feral pigs), makes the US suitable for JEV emergence. In fact, the US is the world’s third-largest producer and consumer of pork and pork products (ERS, USDA 2022). The importance of the swine industry to the US economy and the sizeable naïve pig populations, magnify the severity of a potential viral incursion. As pigs are considered the main amplifying host of JEV, an extensive review of the literature and identification of knowledge gaps will assist researchers, stakeholders, and policy makers with effort prioritization, development of precautionary intervention measures, and evaluation of disease control measures. Although current conditions have not been favorable for JEV to establish in the US, increases in international trade and globalization, as well as changes in climate and land use, and reductions in pesticide use, can contribute to its rapid and wide geographical spread (Oliveira et al., 2018). A good understanding of the role of swine as an amplifying host for this virus is critical to public health authorities when planning prevention and preparedness measures.