Assessing Dengue Virus Importation Risks in Africa: A Climate and Travel-Based Model

Abstract

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

Methods: The risk of dengue introduction into Africa from countries of high incidence in Africa, 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, along with travel information in a risk flow model, to estimate importation risk.

Findings: We find that countries in East Africa face higher estimated risk of importation from Asia and other East African countries, whereas for West African countries, larger risk of importation is estimated from within the region. Some countries with high risk of importation experience low local transmission suitability which likely hampers the chances that importations lead to local transmission and establishment. Conversely, Mauritius, Uganda, Ivory Coast, Senegal, and Kenya are identified as countries susceptible to dengue introductions during periods of persistent transmission suitability.

Interpretation: Our work 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. This will be critical in detecting and managing imported cases and can improve local response 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.org, Oxford Martin School Pandemic Genomics programme, John Fell Fund.

Keywords: Africa; Arboviruses; Dengue; Introductions; Mobility; Risk Flow.

Figure 1.. Mean risk of dengue introduction into African countries in 2019 from 14 countries in Asia and Latin America.

The risk of dengue introduction into African countries from 14 origin countries in Asia and Latin America is represented by circles on the African continent. The size of the circles represent the size of the risk averaged over the 12 months 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.

Figure 2:. Mean risk of dengue introduction into African countries in 2019 from 18 African countries with Dengue circulation.

Originating African countries considered here are Chad, Sao Tome and Principe (Central Africa), Comoros, Ethiopia, Kenya, Tanzania (East Africa), Benin, Burkina Faso, Ghana, Guinea, Mali, Niger, Nigeria, Senegal, Togo (West Africa), Angola, Mauritius (Southern Africa) and Mauritania (Northern Africa). 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 represent the size of the risk averaged over the 12 months for each airport in Africa. The border 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.

Figure 3.. Time-varying risk of introduction into selected African countries in 2019.

The blue, red and orange lines represent the risk of importation from Asia, South America and Africa, respectively, and the dotted line represents the total risk of importation from both continents and African countries across the year. 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. The CS value represents the cosine similarity between the two timelines, where a value of 0 indicates low synchrony and a value of 1 indicates high synchrony. Here, we demonstrate countries that had the most synchronicity between transmission suitability and risk of introduction - see supplementary S7, p.6 for additional countries.

Figure 4:. Overall proportional risk of importation into African countries before and after adjusting for period of persistence suitability (transmission suitability greater than 1).

A) The proportion of risk from Asia,South America and African regions throughout the year for each district. The size of the pie charts are proportional to mean risk of importation across the year and the coloured pies represent the origin continent/region. We zoomed in on specific countries within the plot, namely: Ghana, Togo, Benin, Nigeria, Rwanda, Uganda, Senegal Tanzania, Egypt, Sudan, Ethiopia, and Kenya. B) The proportion of risk from Asia,South America and African regions across the year, for months with high persistence suitability. We zoomed in on specific countries within the plot, namely: Ghana, Togo, Benin,

Figure 5:. Risk of Dengue importation into various African countries, grouped by regions: East Africa, West Africa, Central Africa, Northern Africa and Southern Africa.

Boxplot of risk across months and districts with high persistence suitability. Africa in orange, Aisa in blue and South America in red.