Exterminate! Exterminate!

Updated: Oct 29 2007, 07:23am hrs
Weve made vaccines from pus and poop, we make them now using eggsso why not make them in live mosquitoes So says Stefan Kappe, a researcher at the Seattle Biomedical Research Institute. To prove the point, his team is breeding millions of Anopheles mosquitoes and infecting them with malaria-causing parasites.

Not any old parasites, either. Those he uses have had some of their genes knocked out to stop them breeding in humans. Their destiny, like that of the attenuated viral strains grown in eggs, is to form part of a vaccine.

Once the parasites have had time to breed in the mosquitoes, the insects are killed and dissected under a microscope. The gold inside them is their salivary glands, the parts richest in parasites. These are extracted, processed and turned into what Dr Kappe hopes will become a successful vaccine. By injecting this vaccine of pared-down parasites into uninfected individuals, he intends to provoke an immune response to malaria that will be strong enough to kill a real infection before it gets going.

Provoking such a response is, of course, the idea behind any vaccine, and there are various ways of doing it. Dr Kappes looks promising in the laboratory, but has yet to undergo clinical trials. Another method, however, has been on trial for several years by Pedro Alonso of the Barcelona Centre for International Health Research.

The vaccine created by Dr Alonso and his colleagues has been tested on infants aged under five months in a region of Mozambique where the disease is endemic. It did not provide complete protection, but the infection rate observed over the course of the subsequent six months was 65% lower than in members of a control group, who were given a hepatitis B vaccination instead. Unlike Dr Kappes vaccine, this one does not rely on injecting whole, attenuated parasites. Instead, some of the proteins that adorn the parasites surface have been made in bulk. The vaccine is thus, in effect, all surface. Since the immune system can see only the surface of even a whole parasite, that is the only part it can learn to recognise, so a vaccine consisting of parasite surface and nothing else should be good at stimulating an immune responseand it is.

A newish and very effective drug called artemesinin is now being deployed, and the campaign to distribute insecticide-laced bed nets through large parts of Africa is also showing signs of success. A few people are therefore daring to whisper a word that has not been heard much in malaria circles since the 1960s: eradication.

On October 17th, someone dared do more than whisper the word. Bill Gates almost shouted it at a conference on the disease which was organised in Seattle by his foundation. The Gates Foundation helped to finance the trials in Mozambique and Mr Gates used their success to give a rousing speech to the gathered experts, challenging them to raise their sights. Rather than continue with todays strategy of merely controlling malaria, he argued that it is time for the world to aspire to exterminate it altogether.

This is not a new idea. The last attempt to eradicate malaria began in 1955 (coincidentally, the year Mr Gates was born) and relied on a new wonder chemical called DDT to kill the mosquitoes. For a time, it was successful, but then evolution struck back, as natural selection favoured the spread of insecticide-resistant genes. Shortly afterwards, politics struck back, too, as the environmental movement successfully demonised DDT because of the damage it does to many other animals.

Given this history, cynicism about the idea of eradication is understandable. Steven Phillips, chief medical officer of Exxon Mobil, a firm whose African operations are inevitably affected by malaria, argues that eradication is technically impossible and favours emphasis on bread and butter disease control. But Regina Rabinovich and Tachi Yamada, the scientists responsible for running the Gates Foundations anti-malaria effort, argue that eradication was never seriously attempted in Africa in the past.

Eradication would not be cheap. A back-of-the-envelope estimate suggests it would cost about $9 billion a year for two or three decades to make and distribute the necessary vaccines, drugs and equipment. But that compares with $3 billion a year indefinitely, merely to contain the problemnot to mention the economic damage done by the disease. Big ideas have to await the right time to be realised. But for malaria that time may be now.

The Economist Newspaper Limited 2007