A quantitative risk assessment (QRA) of the risk of introduction of the Japanese encephalitis virus (JEV) in the United States via infected mosquitoes transported in aircraft and cargo ships

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

Submitted to: Preventive Veterinary Medicine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2018
Publication Date: 9/24/2018
Citation: Oliveira, A.S., Piaggio, J., Cohnstaedt, L.W., McVey, D.S., Cernicchiaro, N. 2018. A quantitative risk assessment (QRA) of the risk of introduction of the Japanese encephalitis virus (JEV) in the United States via infected mosquitoes transported in aircraft and cargo ships. Preventive Veterinary Medicine. 160(18)1-9. https://doi.org/10.1016/j.prevetmed.2018.09.020.
DOI: https://doi.org/10.1016/j.prevetmed.2018.09.020

Interpretive Summary: We performed a qualitative risk assessment of the likelihood of JEV introduction in the US (manuscript in preparation). The viable pathways of introduction of JEV we 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). 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, varying from low to high, given the presence of both competent vectors and hosts and depending on the area of introduction within the US. Because the probability of establishment of JEV in the continental US was considered negligible, we stopped the risk assessment at this point of the framework. From the pathways identified as viable for the introduction of JEV into the US, only the one pertaining to entry through infected vectors, and specifically via aircraft and cargo ships, was identified as likely in the framework. Thus, these entryways were considered further in a quantitative risk assessment (QRA) model. The objective of this study was therefore to quantitatively assess the risk of introduction of JEV via (1) infected mosquitoes transported in aircraft and (2) cargo ships coming from Asia to the US, by means of a QRA.

Technical Abstract: Following a qualitative risk assessment, in which we identified and assessed all viable pathways for the in-troduction of the Japanese encephalitis virus (JEV) into the United States (US), we identified entry throughinfected vectors via aircraft and cargo ships as the most likely pathway, and thus considered it further in aquantitative risk assessment (QRA) model. The objective of this study was to evaluate the risk of introduction ofJEV in the US via infected mosquitoes transported in aircraft and cargo ships arriving from Asia, using a QRAmodel.We created a stochastic model to quantify the probability of introduction of at least one infected mosquito inthe continental US via aircraft and cargo ships, per at-risk period (March to October) or year, respectively. Wemodeled the following parameters: number offlights (per at-risk period, i.e., March to October) and cargo ships(per year) and per region, number of mosquitoes perflight and ship, number of mosquitoes that were not foundand sensitivity of the mosquito collection method in aircraft, mosquito infection rates, and number of mosquitoescoming in aircraft per at-risk period (March to October) and cargo ships per year. Flight and cargo ship datapertained to years 2010-2016. For model building purposes, we only considered port-to-port vessels arrivingfrom Asia to the US, we assumed that mosquitoes survive the trans-Pacific Ocean ship crossing and that thenumber of mosquitoes in cargo and passengerflights is similar.Our model predicted a very high risk (0.95 median probability; 95% CI = 0.80-0.99) of at least one infectedmosquito being introduced in the US during the at-risk period, i.e., March to October, via aircraft transportationfrom JEV-affected countries in Asia. We also estimated that a median of three infected mosquitoes can enter theUS during the at-risk period, i.e., March to October (95% CI = 1–7). The highest probability of introduction viaaircraft was attributed to the Mediterranean California ecoregion (0.74; 95% CI = 0.50-0.90). We predicted,however, a negligible risk (0; 95% CI = 0.00-0.01) of at least one infected mosquito being introduced via cargoships.Although the risk of introduction of JEV-infected mosquitoes by cargo ships was negligible, the risk viaaircraft was estimated to be high. Ourfindings indicate the need to prioritize JEV prevention and controlmethods for aircraft-based pathways, such as aircraft disinfection. The quantitative estimates provided in thisstudy are of interest to public health entities and other stakeholders, as they may support future interventions forpreventing JEV introduction, as well as other vector-borne diseases, in the US and other countries.