Potential for monkeypox exportation from West and Central Africa through global travel networks

Abstract

Monkeypox virus (MPV) is a zoonotic pathogen endemic to West and Central Africa.1 A growing number of locally acquired MPV cases, across an expanding number of non-endemic countries, is being reported as of May 2022. Prior exported cases of MPV have resulted in secondary transmission, however these were smaller outbreaks.2 Future outbreaks are likely to increase in frequency and size due to the cessation of smallpox vaccine programs, which confers some cross-protection to MPV, coupled with rising global population mobility.3,4 Here, we identify cities at high risk of MPV importation from endemic regions via commercial air travel. We assessed three scenarios of global spread of MPV, originating from: (i) Nigeria, from which at least one exported case was reported on 7 May 2022 to England; (ii) seven countries where the West African clade MPV is endemic; (iii) six countries where the Central African (Congo Basin) clade MPV is endemic. Endemic countries were identified by cross-referencing reported isolates detailed in a recent review5 to a map of countries with evidence of human cases in the past 10 years (e.g. in medical literature or by a public health organization), as of 2021 (Appendix 1). For countries with reported cases but unknown clade, we assigned a clade based on its proximity to countries with known clades. We assumed the West African clade is endemic in Guinea and Togo and the Central African (Congo Basin) clade is endemic in Central African Republic and Equatorial Guinea.5 For each scenario, we identified the top 20 destination cities using modelled volumes and final destination cities of travellers on commercial flights for May 2022. Traveller volumes were modelled using historical flight itinerary data for February 2022 from the International Air Transport Association (IATA) and scheduled flight itineraries (including airport of origin, destination and flight transfers) for May 2022 from CIRIUM, as February 2022 is the most recent complete dataset for global travel trends. IATA data account for an estimated 90% of global commercial air travel, with the other 10% modelled using market intelligence data. Estimated traveller volumes from flights originating in Nigeria in May 2022 are greatest to London, England (27 547), Dubai (9151) and Johannesburg (5706) (Table 1). Countries reporting human cases of West African clade MPV have greatest traveller volumes to London (37 650), Paris (23 801) and Dubai (17 385), whereas countries endemic for Congo Basin clade MPV have the greatest volumes to Paris (16 954), Brussels (6459) and Johannesburg (5749) (Table 1). For reference, May 2019 traveller volumes from these regions can be viewed in Appendix 2. Top 20 cities with the largest modelled air passenger volumes on flights for May 2022 originating from: (1) Nigeria; (2) countries where West African clade MPV is endemic; (3) countries where Central African (Congo Basin) clade MPV is endemic Based on a review by Alakunle et al.5, West African clade MPV is endemic in: Guinea (assumed based on geographic proximity), Sierra Leone, Liberia, Cote D’Ivoire, Ghana, Togo (assumed based on geographic proximity) and Nigeria. Central African (Congo Basin) clade MPV is endemic in: Cameroon, Central African Republic (assumed based on geographic proximity), Equatorial Guinea (assumed based on geographic proximity), Gabon, Democratic Republic of Congo and Republic of Congo. Large European cities such as London and Paris are the most likely distant regions for MPV exportation from endemic regions; however, transmission within the African continent to cities such as Johannesburg is also a possibility. If unrecognized, MPV infections can spread to others, triggering local outbreaks. Limitations of this analysis include assigning clades by geographic proximity where information was not available. In addition, our analysis assumes a homogeneous risk of MPV infection in endemic countries and equal opportunities for populations in these countries to travel internationally. Supporting endemic countries to rapidly identify and effectively manage monkeypox outbreaks is important for local and global control efforts, and may have secondary benefits in mitigating the risk of other emerging pathogens with epidemic or pandemic potential. Such support could include strengthening laboratory capacity and increasing timely access to smallpox vaccination for close contacts. This analysis also identifies non-endemic areas of the world at risk for MPV importation, where heightened awareness by frontline healthcare providers could increase early identification of cases, with timely implementation of appropriate infection control precautions that disrupt further chains of transmission. I.I.B. has consulted to BlueDot (a social benefit company that tracks emerging infectious diseases) and the NHL Players’ Association. K.K. is the founder and CEO of BlueDot. I.I.B., A.T.B., P.A.D. and K.K. conceived the idea N.H.A., M.T.P., A.M., I.I.B. conducted data collection and analysis. All authors contributed to the interpretation and writing of the manuscript. Grants or Other Financial Support: IIB is supported by the Canadian Institutes for Health Research.

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