Thursday, October 12, 2006

Why Have We Failed To Control Malaria (and Dengue and Chikungunya)?

Malaria has caused immense suffering to mankind since millennia, killing millions, commoners and kings alike. Having evolved with the human species, the human malaria parasites have stoutly resisted all attempts at wiping them out and have remerged with vengeance, negating some achievements made during the Global Malaria Control Programme of 1950s. Today, malaria causes an estimated 500 million cases a year, kills 2000 African children every day, (that is one African child dying every 30 seconds) and costs an estimated $12 billion a year in lost gross domestic product.

Why is malaria proving such a hard problem? Reasons are many.

  • The malaria parasite exists in two living beings - man, the host who suffers and the female anopheles mosquito, the vector that spreads the disease. Controlling malaria would therefore involve three living beings - the parasite itself, man and mosquito. And two of these, man and mosquito- are moving, spreading malaria from person to person, place to place, even across continents in this jet age.
    • Malaria parasite has the great ability to escape human defenses - the immune system and can survive within the host for years without harming him, but spreading through the mosquito. Compare this with the HIV that causes AIDS and Mycobacterium tuberculosis, the bacteria causing Tuberculosis or TB. These organisms too have a similar ability and no wonder then that these three infectious diseases are now posing the greatest threat to human health and survival. And this is one reason why a vaccine against malaria may not be as effective, say as the ones against polio, small pox etc, diseases that have no vectors and induce strong immune response.
    • The parasite is controlled with antimalaria drugs. But the first line drug chloroquine, that is cheap and safe, is no more effective in many parts of the world as P. falciparum has developed resistance to it. Newer drugs are very few, expensive (and out of reach to most populations) and more toxic.
    • The host is always moving from place to place, for work or leisure. It is these carriers that spread malaria from one place to another and to people around them. It is an onerous task to track these immigrant workers and treat them. In Mangalooru, the coastal city in southern India where I work, for example, boom in constructions and infrastructure building has brought in thousands of workers from all parts of the country, and many of these are from malarious areas. Their living conditions are pathetic if any, without even a roof over their bodies, leave alone mosquito nets. Their exposed bodies are fertile for the female anopheles to bite. And their workplace often encourages mosquito breeding-stagnant water in tanks, puddles, on the concrete surface for curing etc. So we have the hosts with parasite within and plenty of vectors in one place and malaria spreads to neighbouring areas and thence to the city as a whole. Efforts to track and treat the carrier workers has been found to be the most difficult job: They keep changing their work places, those suffering disappear (most have no addresses and some return home) and many arrive each day by buses and trains and it is difficult to screen all of them.
    • Mosquitoes are ubiquitous and more adapted than humans are, being on this planet at least 40 times as long as humans. Breeding profusely in stagnant water, made available in plenty around human habitations, the mosquitoes are difficult to control once they develop wings and start flying. And to add to the woes, even mosquitoes have developed resistance against insecticides.

Is it hopeless then? Parasites are resistant, mosquitoes are tiny, flying and defy insecticides and man is moving and difficult to track and mend. Hope, if at all, lies in the non-flying mosquito larvae. The great Sir Ronald Ross showed it way back in 1900. But we don't learn simple lessons, or DO NOT want to! Just reduce the man made sources of mosquito breeding and that's it! But then what is the problem? No mosquitoes - no insecticides; no malaria - no vaccines, no anti malaria drugs!

Look at how resources for malaria control are meager on the one hand and mostly spent on research rather than simple measures of source reduction on the other.

Malaria gets a fraction of what other less common and less deadly diseases get. In the mid nineties, it was estimated that only about $85 million a year is spent globally on malaria research, about half as much as spent on asthma research. During the same time, a British study estimated that each year $3,274 was spent on AIDS research for each fatal case of AIDS, while $65 was spent on malaria research for each fatal case of malaria. It is estimated that in 2004, total spending on research and development for the disease amounted to $323 million, representing about 0.3% of total health research and development investments. But, malaria is responsible for 3% of all the lost years of productive life caused by all diseases worldwide. By contrast, diabetes gets about 1.6% of the total money spent on medical research, while it accounts for 1.1% of all the productive years of life lost to disease. In other words, the disease burden to society is about one-third of that of malaria, but it gets nearly six times more money in research and development funding.

The Gates Foundation's contribution to malaria in 2005-2006 is reportedly distributed thus:

  • $107.6 million to the PATH Malaria Vaccine Initiative (MVI)
  • $100 million to the Medicines for Malaria Venture (MMV)
  • $50.7 million to the Innovative Vector Control Consortium (IVCC), led by the Liverpool School of Tropical Medicine, to fast-track development of improved insecticides and other mosquito control methods.

A fully-funded malaria control effort - which could cut malaria deaths in half by 2010 - will cost an estimated $3.2 billion annually, but only a fraction of this amount is being spent per year.

Lesser emphasis on source reduction probably explains lack of public participation in malaria control. In Mangalooru, our experience is the same. The officials and workers at the City Corporation, the elected representatives of the City Corporation, the Corporators and the general public all alike clamour for spraying and fogging. And point fingers at each other. The IEC activities conducted over the past 10 years, including door-to-door campaigning, hoardings, films and other audio-visual materials, have all been not so effective in motivating the public to clear the water stagnation in their own surroundings. Every one seems to wait for the spray worker to arrive and spray the chemicals, often into flower pots, gutters and gardens. Chemicals worth lakhs of rupees are dumped on the surroundings of human dwellings and mosquitoes that breed in clean stagnant water are left untouched!

And now, if Dengue and Chikungunya, spread by Aedes aegyptii, a mosquito that breeds in the same situations as Anopheles of malaria, are making headlines and causing headaches to the administrators, the problem lies again in sources of mosquito breeding and the answer is SOURCE REDUCTION.

See My Web Site On Malaria http://www.malariasite.com

Must Read:

Aedes Aegypti and Aedes Aegypti-borne Disease Control in the 1990s: Top Down or Bottom Up
Duane J. Gubler 49th Franklin Craig Lecture delivered before the American Society of Tropical Medicine & Hygiene, Washington, DC 12/7/88 Available at http://wonder.cdc.gov/wonder/PrevGuid/p0000434/p0000434.asp

Also See:

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