Potential for Zika virus introduction and transmission in resource-limited countries in Africa and the Asia-Pacific region: a modelling study

Abstract

Background: As the epidemic of Zika virus expands in the Americas, countries across Africa and the Asia-Pacific region are becoming increasingly susceptible to the importation and possible local spread of the virus. To support public health readiness, we aim to identify regions and times where the potential health, economic, and social effects from Zika virus are greatest, focusing on resource-limited countries in Africa and the Asia-Pacific region.

Methods: Our model combined transportation network analysis, ecological modelling of mosquito occurrences, and vector competence for flavivirus transmission, using data from the International Air Transport Association, entomological observations from Zika's primary vector species, and climate conditions using WorldClim. We overlaid monthly flows of airline travellers arriving to Africa and the Asia-Pacific region from areas of the Americas suitable for year-round transmission of Zika virus with monthly maps of climatic suitability for mosquito-borne transmission of Zika virus within Africa and the Asia-Pacific region.

Findings: An estimated 2·6 billion people live in areas of Africa and the Asia-Pacific region where the presence of competent mosquito vectors and suitable climatic conditions could support local transmission of Zika virus. Countries with large volumes of travellers arriving from Zika virus-affected areas of the Americas and large populations at risk of mosquito-borne Zika virus infection include India (67 422 travellers arriving per year; 1·2 billion residents in potential Zika transmission areas), China (238 415 travellers; 242 million residents), Indonesia (13 865 travellers; 197 million residents), Philippines (35 635 travellers; 70 million residents), and Thailand (29 241 travellers; 59 million residents).

Interpretation: Many countries across Africa and the Asia-Pacific region are vulnerable to Zika virus. Strategic use of available health and human resources is essential to prevent or mitigate the health, economic, and social consequences of Zika virus, especially in resource-limited countries.

Funding: Canadian Institutes of Health Research and the US Centers for Disease Control and Prevention.

Figure 1. Seasonal geographical suitability for Zika virus transmission in Africa and seasonal volume of airline travellers arriving from the Americas

Monthly maps are shown for Africa. Travellers arriving from the Americas refers to travellers originating from regions of Latin America and the Caribbean that are suitable for year-round transmission of Zika virus.

Figure 2. Seasonal geographical suitability for Zika virus transmission in Asia-Pacific and seasonal volume of airline travellers arriving from the Americas

Monthly maps are shown for Asia-Pacific region. Travellers arriving from the Americas refers to travellers originating from regions of Latin America and the Caribbean that are suitable for year-round transmission of Zika virus.

Figure 3. Volume of airline travellers arriving from the Americas by peak resident population at risk of Zika virus exposure and health expenditures per capita

The x-axis shows log of the annual volume of travellers arriving from airports within the ecological niche of Zika virus in the Americas, y-axis shows the transformation of health expenditures per capita (square root of 1/health expenditures per capita), and the size of circles shows the populations residing within the geographical range of Zika virus during the month of its broadest activity. Travellers arriving from the Americas refers to travellers originating from regions of Latin America and the Caribbean that are suitable for year-round transmission of Zika virus. Due to highly skewed distribution of values, volume of airline travellers was plotted on a logarithmic scale. Population at risk of Zika virus exposure refers to resident populations living in areas suitable for Zika virus transmission during the month when the geographical range of suitability is broadest. Health expenditures are measured in 2014 US$; because of highly skewed distribution of values, we transformed health expenditures per capita for visualisation purposes.