World Malaria Day: Emerging threats but reasons to be hopeful

News article 25 Apr 2024
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As we mark World Malaria Day, it is important to remember that malaria remains a major health problem worldwide, say LSTM researchers

As we mark World Malaria Day, it is important to remember that malaria remains a major health problem worldwide. In 2022, the World Health Organization (WHO) estimated that 249 million malaria cases occurred in 85 endemic countries, with 94% of cases reported from Africa.

Since 2015, malaria progress has stalled globally, calling for intensified malaria control efforts. Resistance, climate change and funding are all global threats to effective prevention and treatment – but there are also reasons to be hopeful through new vaccines and the research efforts of the international scientific community, including here at Liverpool School of Tropical Medicine (LSTM).

The WHO and member states are committed to providing universal coverage with effective vector control – methods to stop the spread of mosquitoes that carry the disease - to protect individuals at risk of malaria, including long-lasting nets treated with insecticide and supplemented by spraying of insecticides to residual surfaces in the home, such as indoor walls.

The rapid spread and emergence of insecticide resistance necessitates new tools as well as the smarter use of ones that have been proven to work in the past.

While nets are highly effective and cost-effective, mounting evidence suggests that they alone will not be sufficient to achieve malaria control targets and elimination goals. Widespread resistance to the types of insecticides that have been shown to be effective, inadequate coverage with nets, changes in mosquitoes that carry malaria and their behaviours, increased outdoor biting, and transmission that persists even after preventative measures all threaten this.

The rapid spread and emergence of insecticide resistance necessitates new tools as well as the smarter use of ones that have been proven to work in the past. Changes in mosquito biting times to when people are less likely to be protected by nets highlights the need for tools that are don’t need to be ‘turned on’ by people. Currently available tools include indoor residual spraying, which is well-established, highly effective, and cost-effective. However, this is difficult to roll out and expensive, which means it is not always used effectively. In 2022, the WHO estimated that only 1.8% of those at risk of malaria was protected by indoor residual spraying, down from 5.5% in 2010. Cost-effective vector control interventions are needed to fill coverage gaps, increase protection against malaria, and guard against the emergence and spread of insecticide resistance.

The many effects of climate change also represent a threat to the spread of malaria, as do new, invasive mosquito species that are seeing the disease affect urban populations. At LSTM, we are leading on research to better understand the spread of Anopheles stephensi, a mosquito usually found in South Asian cities which is threatening control efforts in the Horn of Africa after being identified in towns and cities there.

A significant funding gap is also a concern. In total, an estimated US $9.3 billion annually is required to reach WHO’s malaria control milestone targets in 2025, however, the funding gap between resources available and estimated need was US $3.7 billion in 2022.

The many effects of climate change also represent a threat to the spread of malaria, as do new, invasive mosquito species that are seeing the disease affect urban populations

New tools (reasons to be hopeful)

However, there are reasons to be hopeful. In 2021, the (WHO) issued a strong recommendation approving a malaria vaccine for prevention of P. falciparum malaria in children living in areas where malaria is a likely risk, known as RTS,S. The evidence supporting this vaccine included a trial involving over 15,000 children from 7 countries, with a further study evaluating around 2 million children receiving the vaccine in Kenya, Malawi and Ghana. Following WHO’s recommendation, countries requested 80–100 million doses of RTS,S per year, far exceeding the limited supply. A second malaria vaccine was approved by WHO in 2023 and is expected to boost the available supply of vaccine to meet the high demand.

New technologies and innovative methods to prevent malaria transmission also offer hope. For example, new ‘spatial repellents’ – commonly devices that continuously emit insecticide in enclosed spaces – could have further benefits. It is hoped that the results of two recent trials of their effectiveness could provide positive evidence needed to inform WHO guidelines and policy recommendations for vector control.

However, there are reasons to be hopeful. In 2021, the (WHO) issued a strong recommendation approving a malaria vaccine for prevention of P. falciparum malaria in children living in areas where malaria is a likely risk

There is also promise in research to better understand the genetics of mosquitoes, much led here at LSTM, which will allow us to identify new biological targets for designing new interventions. It will also allow us to understand the causes of insecticide resistance, identify them rapidly in the field and adjust our control strategies accordingly in order to slow the emergence of resistance and give us another tool in the global fight against malaria.