Abstract
BackgroundZika virus (ZIKV) emerged as a global epidemic in 2015–2016 from Latin America with its true geographical extent remaining unclear due to widely presumed underreporting. The identification of locations with potential and unknown spread of ZIKV is a key yet understudied component for outbreak preparedness. Here, we aim to identify locations at a high risk of cryptic ZIKV spread during 2015–2016 to further the understanding of the global ZIKV epidemiology, which is critical for the mitigation of the risk of future epidemics.MethodsWe developed an importation simulation model to estimate the weekly number of ZIKV infections imported in each susceptible spatial unit (i.e. location that did not report any autochthonous Zika cases during 2015–2016), integrating epidemiological, demographic, and travel data as model inputs. Thereafter, a global risk model was applied to estimate the weekly ZIKV transmissibility during 2015–2016 for each location. Finally, we assessed the risk of onward ZIKV spread following importation in each susceptible spatial unit to identify locations with a high potential for cryptic ZIKV spread during 2015–2016.ResultsWe have found 24 susceptible spatial units that were likely to have experienced cryptic ZIKV spread during 2015–2016, of which 10 continue to have a high risk estimate within a highly conservative scenario, namely, Luanda in Angola, Banten in Indonesia, Maharashtra in India, Lagos in Nigeria, Taiwan and Guangdong in China, Dakar in Senegal, Maputo in Mozambique, Kinshasa in Congo DRC, and Pool in Congo. Notably, among the 24 susceptible spatial units identified, some have reported their first ZIKV outbreaks since 2017, thus adding to the credibility of our results (derived using 2015–2016 data only).ConclusionOur study has provided valuable insights into the potentially high-risk locations for cryptic ZIKV circulation during the 2015–2016 pandemic and has also laid a foundation for future studies that attempt to further narrow this key knowledge gap. Our modelling framework can be adapted to identify areas with likely unknown spread of other emerging vector-borne diseases, which has important implications for public health readiness especially in resource-limited settings.
Highlights
Zika virus (ZIKV) emerged as a global epidemic in 2015–2016 from Latin America with its true geographical extent remaining unclear due to widely presumed underreporting
We aim to answer the following key questions, focusing on all countries or first-level subdivisions where no indigenous Zika cases were reported during the 2015–2016 global epidemic: (i) At least how many ZIKV infections were imported in each country or subdivision during 2015–2016 and to what extent were imported ZIKV infections underreported? (ii) Which countries or subdivisions were most likely to experience cryptic ZIKV
Model validation results We observed a high correlation between the estimated total number of imported ZIKV infections and the reported case count during 2015–2016 for each susceptible spatial unit in the US (Pearson r = 0.913 for log10 transformed data)
Summary
Zika virus (ZIKV) emerged as a global epidemic in 2015–2016 from Latin America with its true geographical extent remaining unclear due to widely presumed underreporting. We aim to identify locations at a high risk of cryptic ZIKV spread during 2015–2016 to further the understanding of the global ZIKV epidemiology, which is critical for the mitigation of the risk of future epidemics. The first autochthonous ZIKV case in Europe was reported in October 2019 with its source remaining unknown at the time of writing [8], which underscores our limited understanding of the virus's epidemiology. ZIKV is no longer a public health emergency, the potential reoccurrence of future large-scale epidemics remains a concern, which necessitates continued investments in ZIKV research and surveillance in preparation for such an event [9]
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