Dengue virus importation risks in Africa: a modelling study

Abstract

Background: Dengue is a significant global public health concern that poses a threat in Africa. Particularly, African countries are at risk of viral introductions through air travel connectivity with areas of South America and Asia in which explosive dengue outbreaks frequently occur. Limited reporting and diagnostic capacity hinder a comprehensive assessment of continent-wide transmission dynamics and deployment of surveillance strategies in Africa. In this study, we aimed to identify African airports at high risk of receiving passengers with dengue from Asia, Latin America, and other African countries with high dengue incidence.

Methods: For this modelling study, air travel flow data were obtained from the International Air Transport Association database for 2019. Data comprised monthly passenger volumes from 14 high-incidence countries outside of Africa and 18 countries within the African continent that reported dengue outbreaks in the past 10 years to 54 African countries, encompassing all 197 commercial airports in both the source and destination regions. The risk of dengue introduction into Africa from countries of high incidence in Asia, Latin America, and within Africa was estimated based on origin-destination air travel flows and epidemic activity at origin. We produced a novel proxy for local dengue epidemic activity using a composite index of theoretical climate-driven transmission suitability and population density, which we used, in addition to travel information in a risk flow model, to estimate importation risk.

Findings: Countries in eastern Africa had a high estimated risk of dengue importation from Asia and other east African countries, whereas for west African countries, the risk of importation was higher from within the region than from countries outside of Africa. Some countries with high risk of importation had low local transmission suitability, which is likely to hamper the risk that dengue importations would lead to local transmission and establishment of a dengue outbreak. Mauritius, Uganda, Côte d'Ivoire, Senegal, and Kenya were identified as countries susceptible to dengue introductions during periods of persistent transmission suitability.

Interpretation: Our study improves data-driven allocation of surveillance resources, in regions of Africa that are at high risk of dengue introduction and establishment, including from regional circulation. Improvements in resource allocation will be crucial in detecting and managing imported cases and could improve local responses to dengue outbreaks.

Funding: Rockefeller Foundation, National Institute of Health, EDCTP3 and Horizon Europe Research and Innovation, World Bank Group, Medical Research Foundation, Wellcome Trust, Google, Oxford Martin School Pandemic Genomics programme, and John Fell Fund.

Figure 1

Mean risk of dengue introduction into African countries in 2019 from 14 countries in Asia and Latin America The size of the circles represents the mean risk of dengue importation in 2019 for each airport in Africa. The colour of the circles represents the country from which the risk is coming from and the fill colour of those countries are consistently matched. The fill colour of the African continent represents the index of transmission suitability multiplied by population density to highlight the hotspots of high transmission at the destination. AGO=Angola. BDI=Burundi. BEN=Benin. BFA=Burkina Faso. BGD=Bangladesh. BLZ=Belize. BOL=Bolivia. BRA=Brazil. BWA=Botswana. CAF=Central African Republic. CIV=Côte d’Ivoire. CMR=Cameroon. COD=Democratic Republic of the Congo. COG=Republic of the Congo. COL=Colombia. COM=Comoros. DJI=Djibouti. DZA=Algeria. EGY=Egypt. ERI=Eritrea. ETH=Ethiopia. GAB=Gabon. GHA=Ghana. GIN=Guinea. GMB=The Gambia. GNB=Guinea-Bissau. GNQ=Equatorial Guinea. IND=India. KEN=Kenya. KHM=Cambodia. LBR=Liberia. LBY=Libya. LKA=Sri Lanka. LSO=Lesotho. MAR=Morocco. MDG=Madagascar. MLI=Mali. MOZ=Mozambique. MRT=Mauritania. MUS=Mauritius. MWI=Malawi. MYS=Malaysia. NAM=Namibia. NER=Niger. NGA=Nigeria. NIC=Nicaragua. PER=Peru. RWA=Rwanda. SDN=Sudan. SEN=Senegal. SGP=Singapore. SLE=Sierra Leone. SOM=Somalia. SSD=South Sudan. STP=São Tomé and Príncipe. SWZ=Eswatini. SYC=Seychelles. TCD=Chad. TGO=Togo. THA=Thailand. TUN=Tunisia. TZA=Tanzania. UGA=Uganda. VNM=Viet Nam. ZAF=South Africa. ZMB=Zambia. ZWE=Zimbabwe.

Figure 2

Mean risk of dengue introduction into African countries in 2019 from 18 African countries with dengue circulation The risk of dengue introduction into African countries is represented by circles on the African continent coloured by the corresponding region of the originating African country. The size of the circles represents the size of the risk averaged over the 12 months for each airport in Africa. The borders for African countries considered as originating locations in the study are outlined in black. The fill colour of the African continent represents the index of transmission suitability multiplied by population density to highlight the hotspots of high transmission at the destination. AGO=Angola. BDI=Burundi. BEN=Benin. BFA=Burkina Faso. BWA=Botswana. CAF=Central African Republic. CIV=Côte d’Ivoire. CMR=Cameroon. COD=Democratic Republic of the Congo. COG=Republic of the Congo. COM=Comoros. CPV=Cabo Verde. DJI=Djibouti. DZA=Algeria. EGY=Egypt. ERI=Eritrea. ETH=Ethiopia. GAB=Gabon. GHA=Ghana. GIN=Guinea. GMB=The Gambia. GNQ=Equatorial Guinea. KEN=Kenya. LBR=Liberia. LBY=Libya. LSO=Lesotho. MAR=Morocco. MDG=Madagascar. MLI=Mali. MOZ=Mozambique. MRT=Mauritania. MUS=Mauritius. MWI=Malawi. NAM=Namibia. NER=Niger. NGA=Nigeria. RWA=Rwanda. SDN=Sudan. SEN=Senegal. SLE=Sierra Leone. SOM=Somalia. SSD=South Sudan. SYC=Seychelles. TCD=Chad. TGO=Togo. TUN=Tunisia. TZA=Tanzania. UGA=Uganda. ZAF=South Africa. ZMB=Zambia. ZWE=Zimbabwe.

Figure 3

Time-varying risk of dengue introduction into African countries in 2019 The risk of importation was aggregated at the national level by summing the individual risks from all airports within each African destination country. The blue bars represent the time-varying transmission suitability index. For CS, a value of 0 indicates low synchrony and a value of 1 indicates high synchrony. In this figure, the countries shown had the most synchronicity between transmission suitability and risk of introduction. Additional countries are shown in the appendix (p 6). CS=cosine similarity.

Figure 4

Overall proportional risk of dengue importation into African countries before and after adjusting for period of persistence suitability (transmission suitability >1) (A) The proportion of risk from Asian, South American, and African regions throughout the year for each district. The size of the pie charts is proportional to the mean risk of importation and the colours correspond to the origin continent or region. (B) The proportion of risk from Asian, South American, and African regions across the year, for months with high persistence suitability.

Figure 5

Risk of dengue importation into African countries in 2019 Boxplots of dengue importation risk in 2019 in African districts with high persistence suitability (P index >1). Boxes indicate the 25th and 75th percentiles, the horizontal lines in the boxes indicate the median values, whiskers indicate the range, and the datapoints outside of the whiskers are outliers.