Introduction of the Japanese encephalitis virus (JEV) in the United States – a qualitative risk assessment

Authors: OLIVEIRA, ANA R. - Kansas State University; PIAGGIO, JOSE - Universidad De La República; Cohnstaedt, Lee; McVey, David; CERNICCHIARO, NATALIA - Kansas State University

Submitted to: Transboundary and Emerging Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2019
Publication Date: 3/22/2019
Citation: Oliveira, A.S., Piaggio, J., Cohnstaedt, L.W., McVey, D.S., Cernicchiaro, N. 2019. Introduction of the Japanese encephalitis virus (JEV) in the United States – a qualitative risk assessment. Transboundary and Emerging Diseases. 66:1558-1574. https://doi.org/10.1111/tbed.13181.
DOI: https://doi.org/10.1111/tbed.13181

Interpretive Summary: We determined that the probability of infection of a first local host and the probability of onward spread of JEV by local vectors to local hosts were variable. For JEV introduction via adult vectors and animal hosts (through all pathways), probabilities may vary from low to very high, depending on specific vector and host parameters that are too complex to fully acknowledge in a RA, the specific path of introduction considered, and the area being assessed. For all other pathways, however, these probabilities were deemed very low. Based on our literature search, we theorize that the short periods of viremia in hosts (two to four days in pigs and ardeid birds), the probable limited (and variable) availability of hosts near airports, the variability of contact rates between hosts and vectors, differences in JEV genotype and strain, environmental factors, idiosyncrasies related to weather conditions, cross-protection of JEV with other circulating Flaviviruses, such as the West Nile virus (WNV) and the St. Louis encephalitis virus (SLEV), and the lability of JEV in the environment do not support JEV establishment in the US. Regarding the influence of JEV genotype in JEV transmission risk, genotype I (the most dominant genotype in some JEV endemic regions, including China) has enhanced replication efficiency in avian hosts compared to genotype III (higher viremia titers and longer viremic duration). This has probably resulted in higher exposure and consequent infection in mosquitoes, contributing to the efficiency of the bird-associated transmission cycle and elucidating on how JEV genotype and strain may influence 408 the dynamics of JEV transmission.

Technical Abstract: The purpose of this risk assessment (RA) was to qualitatively estimate the risk of emergence of the Japanese encephalitis virus (JEV) in the United States (US). We followed the framework for RA of emerging vector-borne livestock diseases (de Vos et al., 2011), which consists of a structured questionnaire, whose answers to questions can be delivered in risk categories, descriptive statements,or yes or no type of answers, being supported by the literature. The most likely pathways of introduction of JEV identified were: a) entry through infected vectors (by aircraft, cargo ships, tires, or wind), b) import of infected viremic animals, c) entry of viremic migratory birds, d) import of infected biological materials, e) import of infected animal products, f) entry of infected humans, and g) import/production of contaminated biological material (e.g., vaccines). From these pathways, the probability of introduction of JEV through infected adult mosquitoes via aircraft was considered very high and via ships/containers was deemed low to moderate. The probability of introduction via other pathways or modes of entry (vector eggs or larvae, hosts, and vaccines) was considered negligible. The probability of transmission of JEV was variable, ranging from low to high (in the presence of both competent vectors and hosts), depending on the area of introduction within the US. Lastly, the probability of establishment of JEV in the continental US was considered negligible. For that reason, we stopped the risk assessment at this point of the framework. This RA provides important information regarding the elements that contribute to the risk associated with the introduction of JEV in the US. This RA also indicates that infected mosquitoes transported in aircraft (and cargo ships) are the most likely pathway of JEV entry and therefore, mitigation strategies should be directed towards this pathway.