Malaria-- New Tools Needed to Combat an Old Disease

Richard Tren | 28 Apr 2008
The Cutting Edge
April 25th marked World Malaria Day---an occasion to assess progress, galvanize support, and of course, solemnly recognize the suffering that this devastating disease causes.

Every year, over one million people, mostly young children, die from malaria and up to 500 million become ill. However, it need not be this way. Malaria is both preventable and curable. With US taxpayers' money, much is being done to save lives, but investment in new tools and methods of control is essential to sustaining success. The Bill and Melinda Gates Foundation, the National Basketball Association, and Boys and Girls Clubs of America have also contributed funds, and fund-raising, to help eliminate the scourge, especially in Africa. Parts of Africa are considered hyper-endemic since they have transmission rates up to 100 times the rate of those areas where the disease has been eliminated.

Malaria is caused by the plasmodium parasite which is transmitted from person to person by the female Anopheles mosquito. Controlling malaria successfully and breaking the transmission cycle requires treating patients with effective medicines so that parasites are cleared out of the body, as well as controlling mosquitoes.

Targeted mosquito, or vector, control only began in earnest in the early part of the 20th century when scientists discovered how the disease was transmitted. Spraying insecticides on the inside walls of houses where mosquitoes rest was first tried in the 1930s, though these efforts were expensive. However, spraying interior walls appears to be making something of a come-back. At that time the best available insecticide - pyrethrum - only remained effective for approximately two weeks; houses had to be re-sprayed frequently which limited the scope of the programs.

Things changed dramatically with the discovery of DDT.

First used during World War II to prevent the spread of lice-borne typhus, DDT was adopted by malaria control programs into the indoor residual spraying (IRS) programs shortly after the war. DDT is remarkable for several reasons; it is non-toxic to humans and therefore easy to use. It is cheap and very effective against mosquitoes when sprayed on walls. DDT has three main modes of action; it repels mosquitoes which stops them from entering houses where they would feed on humans, it irritates mosquitoes so that if they do enter houses they often exit before feeding, and lastly, if the mosquito is neither repelled nor irritated the chemical will kill it. Perhaps the most remarkable thing about DDT is that it remains effective for up to a year. This long residual action meant that malaria control programs could be expanded, and in the 1950s and 60s malaria was eradicated from many areas, including the US and most of Europe. Countless millions of lives were saved from DDT spraying.

DDT's overuse in agriculture gave it a bad name and led ultimately to its banning for agricultural use. Some countries halted use of DDT and insecticide spraying programs generally as the political tide turned against insecticides. As control programs were scaled back, malaria cases and deaths rose inexorably. In South Africa DDT was removed from malaria control in 1997 and due to insecticide resistance to the alternative chemicals used, malaria cases rose by over 1000% in just three years. In 2000 the South African government reintroduced DDT and malaria cases declined by 80% in one year.

Increasingly, malarial countries are attempting to resuscitate their IRS programs and many wish to use DDT. The US President's Malaria Initiative, which was formed in 2006, aims to spend $1.2 billion over five years to halve the burden of malaria. The PMI is using DDT to prevent malaria in some of the 15 African countries targeted.

Despite the fact that DDT still works well in malaria control, there is a need for more investment and research into alternative insecticides and to find better ways of using the existing tools.

Essentially, IRS is conducted today in much the same was as it was conducted 60 years ago. Over the past few decades, millions of dollars has been spent in the search of a malaria vaccine. Although we are closer now to a vaccine that works than ever before, it will still be some years before it is available. There is of course value in this kind of research, even if it has not produced a workable product yet.

Contrast this however to the astonishing lack of investment in new public health insecticides. The US Government and many other Western governments have devoted countless millions in studies to investigate the potential environmental and human health harm from insecticides, but almost nothing to the search for new insecticides. There has been little investment from the private sector as the search for short-acting agricultural insecticides trumps the need for long-lasting public health insecticides in what remains a tiny market.

Furthermore, the US government is the only major donor providing any substantial support for the IRS intervention itself. Other donors have not funded IRS substantially, probably because it is a more complex intervention than simply providing insecticide treated nets for people to sleep under, the other major malaria control intervention. Currently, some one billion dollars is being spent annually on eliminating malaria worldwide. President Bush's Malaria initiative was launched in 2005 with the goal of spending $1.5 billion over five years.

Most malarial countries have a desperate shortage of trained malaria control officers, medical entomologists, and medical personnel. Here again the US is training malaria program officers to run programs. Of course, malarial countries can change their own policies to prioritize and fund healthcare in an attempt to stem or even reverse the tide of skilled people leaving the countries.

Developing much needed new tools, particularly those for vector control will be essential if the battle against malaria is to be won. In the long run however, it is clear from evidence in many malaria-free countries, that the disease will only be eradicated by increased wealth and development. Malaria epidemics were widespread across the United States and Europe, claiming thousands of lives every year. Two generations have now grown up in these parts without the debilitating and deadly threat from malaria spreading mosquitoes.

Spraying DDT inside houses rid most developed countries of malaria. However, the disease was declining in the 19th century due to increased development, long before we even knew that mosquitoes transmitted the malaria parasites. Mosquito breeding pools were developed for agricultural land and people had better housing, diets, and access to medicines. Ridding Africa of malaria will require a similar process of development so that progress against all diseases can be sustained but, until then, much can be done now to save lives.