What is the burden of vector borne diseases?
Vector-borne diseases are infections transmitted by infected insects such as mosquitoes, sandflies and tsetse flies. Diseases like malaria, leishmaniasis, lymphatic filariasis, dengue and others disproportionately affect poor communities living in low and middle income countries in tropical and sub-tropical zones. The most well-known vector-borne disease, malaria, is a major cause of ill health, particularly in sub-Saharan Africa where there were an estimated 191 million cases and 394,000 deaths in 2015. In addition, the threat from viruses carried by Aedes mosquitoes is growing sharply, with an unprecedented spread of dengue and chikungunya viruses, together with the recent global epidemic of Zika virus disease and major outbreaks of yellow fever. There are an estimated 64 million dengue infections per year in Africa.
What is the link between the built environment and vector-borne diseases?
Poor quality housing and environmental conditions undermine the health of citizens with regard to vector-borne diseases. For example, the home is a place of high risk for malaria transmission, with over 80% of malaria transmission by the night-biting mosquito Anopheles gambiae occurring indoors. Mosquitoes can enter leaky houses through open eaves, doors and windows in order to bite people. Towns and cities undergoing unplanned urbanisation and accompanying environmental degradation provide an ideal habitat for the day-biting Aedes aegypti mosquito. Immature forms of this mosquito are commonly found in plastic containers and discarded tyres which abound due to poor waste management. Insecure water supplies lead to storage of water in containers in the home which also harbour immature forms of Ae. aegypti.
Malaria and other vector-borne diseases are typically prevented through the use of vector control methods such as insecticide-treated bednets. However, in many areas current vector control tools are insufficient to control these diseases. Mosquitoes are also becoming increasingly resistant to the insecticides used against them and the need for non-chemical and inter-sectoral approaches to control is widely recognised. Despite this, improvements to the built environment, traditionally a core pillar of public health, are not often used for vector-borne disease control.
How can we improve the built environment to prevent vector-borne diseases?
There is growing evidence that improving the built environment can be protective against vector-borne diseases. For example, screening houses can be a powerful means to lower transmission of malaria and Aedes-borne diseases. Resilience can also be built into urban environments through better environmental management and urban planning. For example, solid waste management can help to clean up neighbourhoods to remove containers where Aedes mosquitoes lay their eggs. Provision of reliable piped water means that households do not need to store water in their homes. Clearing drains by removing vegetation and rubbish can help to avoid standing water where malaria mosquitoes and those carrying lymphatic filariasis can flourish.
Rapid economic and population growth in sub-Saharan Africa presents a remarkable opportunity to reduce the risk of vector-borne diseases through improvements in the built environment. If nothing is done, then the risk of future outbreaks in the future is huge. The continent’s population is projected to increase from 1.2 billion in 2015 to 2.1 billion in 2050 and it has the world’s fastest rate of urbanisation. Accommodating the expanding population – while working towards Sustainable Development Goal (SDG) 11 and the New Urban Agenda to ensure adequate housing for all by 2030 and safe, resilient human settlements – will require careful planning and hundreds of millions of well-designed new homes.
Leveraging this revolution in rural and urban development should be considered an exceptional opportunity to exert a powerful, continent-wide impact on vector-borne disease control. This aspiration also aligns with the World Health Organization’s (WHO) Global Vector Control Response, at the core of which is inter-sectoral collaboration and the use of interventions outside the health sector, such as improved housing.