Against the mosquito, humans have proved incompetent warriors; but we can win

Malaria kills 1.2 million people each year, according to new research published in the British medical journal Lancet in February 2012.

This is more than twice as many deaths as reported by the World Malaria Report published in 2011.

Africa is hit the hardest, accounting for nearly 81 per cent of malaria deaths globally. These deaths primarily occur among children under five years of age and pregnant women.

How do we turn the tide against an ancient scourge, and ultimately eradicate the canny malaria parasite?

Leading economists have estimated that malaria is responsible for an “economic growth penalty” of up to 1.3 per cent per year in malaria-endemic African countries.

Malaria costs African countries an estimated $12 billion per year (about 36 per cent of Kenya’s annual GDP) in lost productivity.

Treatment of severe episodes takes up to 25 per cent of household income and accounts for up to 40 per cent of public sector health expenditures in sub-Saharan Africa.

Prof Jeffery Sachs of the Earth Institute at Columbia University has shown that the global distribution of per-capita GDP has a striking correlation with malaria and poverty.

The debilitating effect of malaria undermines household productivity.

The real effect of malaria is through the productive time lost by the sick and family members who provide care for the sick. Repeated bouts of malaria in smallholder farm households have been shown to cause a decline in both food security and income.

It is estimated that malaria accounts for about 15 per cent of health-related absenteeism from school and may impair as much as 60 per cent of schoolchildren’s learning ability.

Cross-country studies of percentages of school-age children in school have been inversely linked to the prevalence of malaria.

Malaria and HIV

Scientists have shown that malaria may be accelerating the spread of HIV in areas of sub-Saharan Africa where there is a substantial overlap between the two diseases.

HIV infection disrupts the acquired immune response to malaria, increasing the incidence and severity of malaria.

Acute malaria has been shown to elevate HIV viral load and may increase the risk of HIV transmission. Hence malaria co-infection in HIV-positive individuals could play a key role in promoting the spread of HIV in sub-Saharan Africa.

Human activity through land use and land use change has been recognised as critical to mosquito ecology and vector efficiency.

Studies in western Kenya have shown that deforestation is associated with a marked increase of malaria risk, with vector efficiency increasing by 78 per cent.

Similar studies in the Peruvian Amazon have shown that mosquito-biting rate was 278 times higher in non-forest sites compared with forested areas.

Similarly, a global review of the effect of irrigation and large dams on the burden of malaria revealed that irrigated villages in Rusizi Valley in Burundi had higher malaria prevalence and 150 times higher vector efficiency compared with neighbouring villages without large dams.

Maize pollen is known to provide nutrition for mosquito larvae.

A study published in 2005 in the American Journal of Tropical Medicine and Hygiene showed that the cumulative incidence of malaria in high maize cultivation areas was 9.5 times that in areas with less maize in Ethiopia.

The Intergovernmental Panel on Climate Change (IPCC) concluded that climate change would be associated both with geographical expansion and contraction of malaria distribution.

According to the projections of the integrated weather–disease model, malaria will disappear in the northern Sahel but will expand in the highlands.

An increase in temperature, rainfall, and humidity may cause a proliferation of the malaria-carrying mosquitoes at higher altitudes, resulting in an increase in transmission in areas in which it has not been previously reported.

Under current climate change projections, the East African highlands will turn into malaria epidemic-prone areas by 2050.

Malaria Control Initiatives

International funding for malaria control increased sharply over the past decade, reaching $1.5 billion in 2009.

Increased global funding resulted in robust expansion of antimalarial programmes, with rapid scale-up of distribution of long lasting insecticide-treated mosquito nets – reaching 76 per cent of the population at risk and expansion of indoor residual spaying, reaching 13 million in 2005 to 75 million in 2009.

It also increased the use of rapid diagnostic tests prior to treatment for all patients with suspected malaria from less than 5 per cent at the start of the decade to 35 per cent in 2009.

Because of these interventions, it is estimated that more than 274 million cases and 1.1 million deaths have been avoided in the past decade. 

New commitments for malaria control programmes have stalled, falling short of the estimated $6 billion needed.

This is especially worrying because progress and gains against malaria remain fragile in a majority of high-risk malaria countries in Africa. Moreover, a vaccine against malaria, like an HIV vaccine, remains an elusive goal.

But there is some hope.

A vaccine candidate known as RTS,S/AS01 is in the midst of a large phase three clinical trial.

In his book Mosquitoes, Malaria and Man: A History of Hostilities Since 1880, historian Gordon Harrison wrote of the persistence of malaria:

“Failure so universal, so apparently ineluctable, must be trying to tell us something. The lesson could be of course that we have proved incompetent warriors. It could also be that we have misconstrued the problem.”

Researchers from Australia’s Queensland Institute of Medical Research argue that three factors account for the failure to control malaria, namely: Parasite resistance to safe and affordable anti-malarials and insecticides; the shambolic state of vector control programmes in developing tropical countries; and the failure to develop a vaccine that prevents malaria.

Beyond vaccines, pyrethroids, and antimalarials

To deal robustly with malaria, Africa must look beyond drug therapy, insecticides and vaccines. New strategies for malaria control and prevention must deploy integrated malaria management.

Integrated malaria management solutions include flexible and adaptive management of ecological, environmental, hydrological conditions and knowledge of patterns of malaria transmission, and human settlement planning.

These solutions improve management of reservoirs and irrigation systems; eradicate vector larvae through biological control; reduce vector breeding sites; locate human settlement away from corrals and potential mosquito breeding sites; and provide better housing design and construction.

Integrated solutions work. Studies have shown that the cost of environmental management for malaria in copper mining communities in Zambia is lower than the cost of control programmes that utilise insecticides and chemoprophylaxis implemented in countries like South Africa and Kenya.

For Africa, integrated management is the sensible policy approach. 

Dr Alex O Awiti is the director of the East African Institute at Aga Khan University.