This blog is the seventh in a seven-part series examining the nature and reasons for the near elimination of malaria in Zanzibar since 2000. This question forms the basis of a major new research project and big conversation about malaria led by the Zanzibar Research Centre for Socio-Economic and Policy Analysis (ZRCP). A link to the full report from ZRCP can be found here. This blog follows from Part Six: It is Like a Horror Film, the Villain Keeps Coming Back to Life: The Risks of a Malaria Revival in Zanzibar).

Malaria in Zanzibar: a recap

Malaria is spread to humans through mosquito bites, with symptoms ranging from mild (fever, chills and a headache), to more severe (coma, severe anaemia, seizures, and difficulty breathing), and in too many cases death. Infants, children under 5 years, and pregnant women are at higher risk of severe infection. 

In the early 2000s, the World Health Organization (WHO) estimated there were between 300 and 500 million global cases of malaria a year, resulting in between 700,000 and 2.7 million deaths annually. During that time, 90% of the malaria disease burden was located in Africa.

New evidence on the economic and human cost of malaria in the 1990s helped inspire a renewed global elimination effort. A big push backed by global leaders, funders, and researchers and in Africa governments, health care professionals, volunteers, statisticians, and households was launched in the early 2000s, leading to a dramatic global reduction in the incidence of malaria, and after 2012, the successful trial and later in 2022 the scaling up of a malaria vaccine. After 2015 the WHO verified the complete elimination of malaria in a succession of countries.

Across Africa after 2000, the most successful countries were those that reduced the incidence of and mortality from malaria by 50%. Zanzibar went much further, to near elimination.

Urbanisation in Africa: It’s the Future

According to UN forecasts, between 2018 and 2050 the African urban population will increase from 548 million to 1.34 billion people, from below to more than double that of Europe. There is good reason for optimism. Historically, GDP per capita and urbanization have increased together. Countries that experienced an acceleration of economic growth, such as China after 1980, also experienced accelerated urbanization. Cities have historically been drivers of economic growth. There are well-established theoretical and empirical reasons to link urbanization to explain these economic benefits – the agglomeration benefits of density. Since the 1970s the link between urbanization and industrialization has broken down in Africa. Africa is urbanizing when strikingly poorer than other developing regions. Unable to afford the necessary infrastructure, African cities are often characterized by contagion (exposure to communicable diseases through poor water, sanitation, and hygiene), crime, and congestion (60% of Africa’s urban population lives in slums, and people spend hours each day in traffic). This blog is about a new problem that may add to the list of factors that undermine the economic and social benefits of urbanization in Africa – the Anopheles stephensi mosquito.

Urbanisation and Malaria in Zanzibar and Beyond

Long held assumptions about urbanisation and malaria need re-thinking. In the early 2000s it was noted that the “risk of malaria transmission is qualitatively much greater in rural than urban areas”. While malaria did occur in urban Africa, it was concentrated in the city periphery where small-scale commercial gardens collected surface water. There were some concerns as both the rapid growth of urban populations and the trend of urban-only tourism would likely require attention to malaria in African cities. But the wider thinking was optimistic, that the rapid urbanisation of Africa would “reduce malaria transmission”, where malaria is “uniquely amenable to prevention and control”, through for example “the destruction of aquatic habitats of mosquitoes and expanded access to health care”.

This urban ambivalence needs re-thinking.

A worrying trend is seen in the adaptation of malaria species to the urban environment. Unlike other malaria vectors in Africa, Anopheles stephensi mosquitoes are found not only in rural areas but also in cities, where they breed in human created water containers, such as “household water storage containers and garden reservoirs”. In the context of rapid urbanisation and the emergence of a new urban mosquito malaria control needs to be tackled with an urban-specific strategy. The WHO recognises this and has created a new ‘Global framework for the response to malaria in urban settings’ which the WHO declares is,

“designed to provide guidance to city leaders, health programmers and urban planners as they work to control and eliminate malaria in a rapidly urbanizing world”. The framework was developed in collaboration with UN-Habitat.

The population density of Zanzibar is 768.2 people per square kilometre, more than ten-times that in mainland Tanzania (73.05). There is no long-term economic prospects for mass agriculture and the future of densely populated Zanzibar is very much urban^. In Zanzibar the population of Stone Town (800,000) is growing rapidly as are several urbanized tourist hubs. The second main island, Pemba is much less urbanized. The future of Zanzibar is urban and we hope that urban future is not invaded by malaria spreading Anopheles stephensi. 

If the Future of Malaria is Urban, then Anti-Malaria Policy Needs to Turn Urban

There have many studies that find a lower incidence of malaria in high-quality modern-build urban houses (with metal roofs and brick or concrete walls), examples include in Swaziland between 2012 and 2015; across 21 African countries using data from almost 140,000 children between 2008 and 2015 even after accounting for differences in levels of urbanisation, wealth, and use of malaria interventions; across 72 randomly selected houses in Tanzania on a monthly basis between 2008 and 2011 utilising a detailed study of housing characteristics (eave gaps, wall types, roof types, number of windows, rooms and doors, window screens, house size); a study in the city of Yaounde, Cameroon across 467 randomly selected houses across 32 districts which collected 168,039 mosquitos that found opened eaves, the high number of windows, the presence of holes in walls and living close to breeding sites were associated with high densities of mosquitoes indoor; and a representative sample in 2015 of 8148 households in 329 clusters in Nigeria covering Children aged 6–59 months found an increased prevalence of malaria in houses built completely with unimproved materials. Good quality modern housing protects against malaria regardless of the wider malaria transmission context.

The implications of these studies are that urban malaria control needs to focus on the design, maintenance, and construction of housing and that housing improvements may offer an attractive and sustainable additional strategy to support countries in malaria elimination.

If infections are being acquired within urban areas, malaria control measures must be targeted within those urban areas to be effective. Housing is not the only urban risk factor. Studies have identified a host of risk factors that systematically differ from rural areas including travel history, hotter urban temperatures, more crowded exposure to livestock, proximity to water sources, piped water, and drainage systems. This indicates that in future malaria policy needs to be a multi-sectoral engagement to control urban malaria, including environmental management, improved diagnostics and treatment, socio-economic interventions, and better urban planning.

Any urbanisation of malaria will be bound up with poverty. WHO data from Sub-Saharan Africa shows that malaria prevalence among children aged under 5 years is higher among households living in poverty and decreases with rising economic status, highlighting that wealth strongly influences malaria risk. The poorest urban dwellers suffer a double burden of insufficient protection from malaria transmission due to inadequate housing and living conditions, and limited financial resources. People in low-income households frequently lack the financial means to implement mosquito-proofing measures, making them more vulnerable to mosquito bites at night.

The Future of Africa and Maybe Malaria is Urban: Some Reflections

This blog opened by noting that Africa is urbanising rapidly. We can and should be optimistic about this, noting the potential gains to productivity, employment, innovation, poverty reduction, and ease of service delivery that this may generate. We should also be wary, Africa is urbanising at lower levels of income that has been typical in other parts of the world, in both contemporary and historical experience. African urbanisation is characterised by the impact of the downsides of urban density, including crime, contagion, and congestion. We need to add another danger to this list – the risk of malaria joining this urban revolution. Blog 6¹ in this series argued that Zanzibar, despite undoubted successes over the last two decades, remains vulnerable to a resurgence of malaria. This blog notes that that resurgence could be urban in character.

The bigger takeaway from this paper is that any anti-malaria strategy in Zanzibar going forward must move beyond thinking about malaria as a targeted public health campaign. An anti-malaria strategy needs to consider the economic benefits of malaria elimination, the design of housing, infrastructure, and the interaction between poverty and malaria vulnerability. Treating malaria in the next twenty years requires a more holistic strategy than has been the case for the last twenty years.

It is Like a Horror Film, the Villain Keeps Coming Back to Life: The Risks of a Malaria Revival in Zanzibar