Japanese Encephalitis (JE) is an emerging, zoonotic disease transmitted primarily by Culex species mosquitoes (particularly Culex tritaeniorhynchus) carrying the flavivirus Japanese encephalitis virus (JEV). Japanese encephalitis virus 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) that can cause 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. Effectivity and quality of JE surveillance in endemic countries vary (Jayatilleke et al. 2020), as does availability of diagnostic testing throughout the world. In 2006, the WHO published a position paper on JE vaccines reporting an annual estimation of at least 50,000 new JE cases among those living in countries considered endemic. Campbell et al. (2011) updated prior estimations and predicted a global incidence of JE cases to be nearly 67,900 per year. Most recently, Quan et al. (2020) reported a global estimation of JE incidence of approximately 100,000 per year. 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). Furthermore, JE is an untreatable and incurable disease that, once introduced in a community, 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 the perfect next-stop in the JEV travel itinerary. In fact, the US is the world’s third-largest producer and consumer of pork and pork products (USDA - ERS). The size of the swine industry in the US can not only be positively correlated with the ability of this virus to invade and establish itself, but also to the impact that an incursion would cause to the economy and the populations’ health. As pigs are considered the main amplifying host of JEV, an extensive review of the literature and identification of knowledge gaps may guide researchers, stakeholders, and policy makers on effort prioritization, development of precautionary intervention measures (to prevent JEV introduction), and evaluation of disease control measures (in case of JEV incursion). 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 and executing interventions to control the spread of JEV. Therefore, our objectives are 1) to investigate the role of swine on the risk of JEV transmission in the US as an effort for preparedness in the case of an introduction, and 2) to identify knowledge gaps that may serve as a guide to future research efforts.
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