Targeting mosquito breeding sites could help fight malaria

Stagnant water is found in many towns but help spread malaria. uncultured

As a young civil engineer in the 1950s, my grandfather was posted to Khartoum in the Sudan, tasked with helping to build a new water supply, drains and sewers for the city. Over the years, this system began to leak and became one of the main sources of standing water in which malaria-transmitting mosquitoes breed.

However today, as part of a new concerted effort to control malaria in the city, these pipes are being mended. Other potential breeding sites are also destroyed on a regular basis. Those that can’t be dried out are treated with larvicide and this has contributed to a huge reduction in malaria in the city.

We recently carried out research that suggests that this traditional method of tackling malaria, which aims to prevent mosquitoes from breeding in swampy land and standing water, can have an important role to play in controlling malaria in the future.

Malaria has long been a major source of human illness and death. Today the disease remains a major global public health problem, causing between an estimated 655,000 to 1.24m deaths each year.

Since 2000, great progress has been made in tackling the disease, with massive campaigns to distribute insecticide-treated mosquito bed nets; to spray peoples’ homes with insecticide to kill adult mosquitoes, and to improve diagnosis and treatment. Together, these strategies have helped reduce global malaria mortality by a quarter in the past decade.

However, this success is now threatened by resistance to drugs and chemicals in the malaria parasite and its mosquito carriers, which could render insecticide-treated bed nets, indoor house spraying and widely available drugs less effective. Not only this, but malaria control is expensive. Even at its funding peak in 2011, malaria control fell far short of the US$5 billion required annually and tightened western budgets haven’t helped.

Preventing mosquitoes from breeding in standing water could be an effective and relatively inexpensive supplementary strategy. This method, known as larval source management (LSM), formed the mainstay of early malaria control operations, and was used with great success historically in Brazil, Egypt, Zambia, Indonesia, Europe, the US and many other parts of the world. This approach was famously used to protect workers constructing the Panama Canal from malaria between 1904 and 1914. However, LSM fell out of fashion in the mid-20th century, with the use of DDT for indoor house spraying.

Today, the World Health Organisation recommends LSM as a supplementary malaria intervention, but advocates that further evidence is required to fully support its use in all settings. To evaluate how effective LSM is in preventing malaria, we systematically examined thousands of studies, to identify 13 which met our strict criteria.

We found that LSM reduces the number of people falling ill with malaria by up to three quarters, and the number of people infected with malaria parasites in their blood by up to 90% - which suggests that in certain situations, LSM can be an effective strategy against malaria in Asia and Africa.

LSM is not a panacea. We need to know more before we can support its use in certain contexts; for instance, where swamps or ricefields stretch for many kilometres. As a programme it must also be carefully tailored to local mosquito species and ecology, requiring intensive effort and close management throughout. However, it could prove a relatively low-cost addition to our current suite of malaria interventions.

LSM also heralds a return to a broader approach to controlling this disease by involving sectors outside health. In Khartoum, responsibility for malaria control is shared between the Ministries of Health, Public Works, Agriculture and Education. Together these ministries work to repair damaged water pipes, remove water basins, drain and flush major mosquito breeding sites, and introduce new irrigation techniques that reduce standing water. All at an annual cost of US$600,000 - or around 10 cents per person protected.

Of course, we must continue to advocate for high levels of funding for malaria control. It is also imperative to maintain high coverage with current first line interventions. Insecticide-treated bed nets, indoor house spraying, preventive medication for high-risk groups and good case management are all integral to fighting malaria.