Photograph credits © Jakob Knudsen 2019: left - Kibera, Nairobi, Kenya; right - Drone photo, suburb of Tanga, Tanzania. Houses constructed over an estimated 20 years. The oldest roofs are rusty, the newest in bright colours. Also visible are foundations and half built houses. People build in a long, incremental process whenever money is available.
Dr Lucy Tusting, Assistant Professor at the London School of Hygiene & Tropical Medicine and co-director of the BOVA network, discusses the relationship between housing, urbanisation and health and how housing improvements may reduce malaria transmission.
Q: Could you tell us a little bit about yourself and the focus of your current research?
Lucy Tusting (LT): I’m an infectious disease epidemiologist working on the control of malaria and other vector-borne diseases. My first exposure to health research was in The Gambia, working on a cluster randomised controlled trial of a malaria intervention. I started my research career interested in the relationship between economic development and malaria. This led me to the realisation that the quality of housing was a major factor in determining why the burden of malaria often falls to the poorest households within communities.
Q: Why do you think housing improvements can have an impact in reducing malaria transmission?
LT: People’s homes should be a place of refuge and safety, but unfortunately for vector-borne diseases the opposite is true. Anopheles gambiae, the major African vector of malaria, preferentially bites people indoors at night-time. This means house structure is incredibly important for risk. Eaves, the space between the top of the wall and roof, are typically left open to allow air to circulate. But these are a point of entry for An. gambiae. Simple modifications such as closing the eaves, screening doors and windows and reducing crowing indoors can have a dramatic effect on mosquito densities indoors.
Q: Could you talk a little bit about the relationship between housing, urbanisation and health?
LT: Sub-Saharan Africa has one of the world’s fastest-growing populations. At the same time, the proportion of people living in towns and cities is going up. Consequently, the total number of urban residents is expanding very quickly and is predicted to treble by 2050. Much of this growth is in secondary urban centres and peri-urban areas, where planning, services and infrastructure are poor and unable to keep up with rapid expansion.
Improving housing and the built environment is essential for urban health. Apart from malaria, good housing (including water, sanitation and hygiene) is linked to many other health outcomes known to increase child mortality, such as diarrhoea, anaemia, undernutrition and acute respiratory infection, as well as physical security and mental health.
Our research has shown that Africa’s housing is transforming. Population growth is creating demand for hundreds of thousands of new homes. Economic development is also leading to incremental improvements to existing housing, such as the replacement of thatch roofs with metal or tiles. We have found that from 2000 to 2015, the prevalence of improved housing (with sufficient living area, finished building materials and improved water and sanitation) doubled from 11% to 23%. There is a major opportunity for health if we can tap into these changes.
Q: Evidence suggests that environmental and social factors play a key role in driving poor health outcomes. Could you give more details about this?
LT: Our health is intrinsically linked to the environment – everything from climate to air quality and land use.
Vector-borne diseases are first and foremost a problem of standing water. Aedes aegypti, the primary vector of viruses such as dengue, yellow fever and zika, thrives in small bodies of water created by litter, exposed cisterns and water storage containers, which proliferate in urban areas. Good management of the environment is the backbone of any vector control program.
Social factors are also one of the biggest drivers of ill health. For malaria, the poorest children within communities have approximately double the risk of infection, compared to the least poor children. Economic development is likely to explain part of the reductions in malaria burden across sub-Saharan Africa since 2000. We saw in Uganda that the relationship between malaria and household wealth is mediated by housing quality, nutrition and access to health care. However, these factors are complicated to disentangle – improvements to health can increase wealth, too.
Q: In your opinion, which are the main challenges faced when trying to improve house design?
LT: Historically, the three pillars of public health were water, sanitation and housing. Today, water and sanitation remain firmly on the global health agenda, but housing is neglected. The biggest challenge is that housing falls outside the remit of community health care. To effect change, the health sector must build bridges with architects, engineers, urban planners and city authorities, as we have tried to encourage through the BOVA Network. This has been done very successfully in Khartoum, Sudan, where vector control is tackled across sectors. But it is not easy to do and takes vision and leadership.
Q: How do you think urbanisation can impact malaria transmission, especially in the context of the COVID-19 pandemic in malaria-endemic settings?
LT: Malaria is a growing concern in urban areas, particularly in secondary and peri-urban areas that lack proper planning, infrastructure and housing. The spread of the South Asian urban malaria vector An. stephensi is also a concern, but we do not yet know how this will affect malaria transmission.
Q: In your opinion, which are the next steps that the malaria community should take in order to advance towards malaria elimination?
LT: The immediate priority is to ensure the continued effectiveness of our core interventions – long-lasting insecticide-treated nets (LLINs), indoor residual spraying (IRS), chemoprophylaxis and prompt and effective diagnosis and treatment, accompanied by strong surveillance and program capacity. For example, for LLINs & IRS we need to maintain high coverage and tackle questions of longevity and insecticide resistance. But we also need supplementary strategies to bring down transmission in high burden countries and to achieve elimination in low burden countries. Ultimately, elimination will not be sustained by technological solutions, but by economic and environmental factors. Improvements to housing and the built environment are central to this.
Dr Tusting is an infectious disease epidemiologist and holds an MRC fellowship. She is an Assistant Professor at the London School of Hygiene & Tropical Medicine and co-director of the BOVA network. Her research applies epidemiological and statistical methods to understand the dynamics of infectious diseases and improve prevention and control, particularly of malaria.