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Zanzibar: Where have all the patients gone?

October 6, 2009 - 09:38 -- Bart G.J. Knols

In a recent commentary published by CNN, Tachi Yamada, President of the Global Health Programme at the Bill & Melinda Gates Foundation, expressed his euforism about the malaria control activities on the island of Zanzibar. And not without reason. He visited a paediatric ward and found empty beds. No sick children, no suffering because of malaria. Indeed a reason to be happy. Zanzibar has hammered malaria over the last five years to the extent where it 'has virtually eliminated the disease' according to Yamada.

But note the word 'virtually' in this sentence. Does 'virtually' mean 'almost', in the sense that activities will continue until eradication is accomplished? Or does it mean 'we've accomplished a great reduction in malaria and that's it'. Let's review both meanings here and try to make sense of what is said here.


First, suppose Yamada meant that 'virtually' indicates that control activities will continue until the disease has disappeared from the island. Eradicated. Gone. The only way in which this could possibly be done is by wiping out all the mosquitoes on the island. Eradicating the vector, not the parasite. If mosquitoes would not be eradicated than people from the mainland would bring in parasites and re-ignite malaria transmission. The question thus becomes: How does one eradicatie the malaria vector from the island? The currently used methods, indoor-residual spraying and treated nets, may help to get rid of Anopheles funestus, but An. gambiae will remain. An all-out war that would include area-wide treatment of breeding sites would be needed. And if this would succeed, re-introduction of the mosquito from the mainland is to be feared.


If Yamada merely pointed to the huge drop in cases without any further assumptions that eradication efforts would follow, then a scenario that existed in the late 1950s surfaces once more. Following intensive spraying on Zanzibar with Dieldrin, and later DDT, malaria was, just like now, almost history in those days. It was 'virtually' eliminated. Ten years later, after spraying had stopped, prevalence levels were at par with those before the campaign. The situation that Yamada is so pleased with is therefore a repetition of the past. And as Einstein said: 'If you do what you did, you get what you got'. In other words, unless the millions of dollars will continue to flow into Zanzibar and operations can be sustained, the euforism will disappear. Slowly but surely.


In the late 1950s, the annual number of malaria cases in Sri Lanka had dropped from 2.5 million to a mere 17, after intensive spraying campaigns. No doubt, if Yamada would have been involved then he would have written a similar commentary for CNN. But we all know what malaria is like on Sri Lanka today.


Time for a poll: Will Zanzibar eradicate malaria in the next five years?