Prick against the Prick

18. February 2009
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From the bark of the cinchona to DDT. All approaches to wipe out malaria in the tropes were just as versatile as unsuccessful so far. An effective vaccine could at least stem the epidemic in a couple of years.

Africa is free of malaria. An utopia our generation won’t live to see? If the mathematical calculations of Gabriela Gomes at the Portugues Instituto Gulbenkian de Ciência are correct, we can stop the occurrence of malaria at least in regions with moderate transmission. Only few areas in Africa do not fulfil that criterion. Although the article in the professional magazine PLoS ONE conceals which remedy would be most suitable.

Resistances against the mugwort-active ingredient

According to Unicef 800,000 children die every year from this tropical disease, other estimates figure triple as many. With completely different approaches, tropical disease specialists try to stem the disease which is still threatening the future of Africa as well as of South East Asia and Latin America. A combination therapy with Artemisinin has proven to be effective over the past years. The active ingredient of the annual mugwort has shown good results in several studies. And it has an additional advantage: The plant grows locally. With a little know how, effective medications can be produced in countries without a billion dollar budget. At the conference of the American tropical disease specialists last fall in New Orleans several articles pointed to the back of the oh-so-shining medal. In Cambodia where the mugwort active ingredient often is applied without any additional therapy, more and more resistances of the parasite occur. The wall of optimism and confidence in the fight against malaria starts getting first cracks.

Vaccines: Exact function unknown, results good

Where effective therapies fail the hope on vaccines remains to nip the break out in the bud. The most promising candidate currently is a vaccine against a sporozoit-antigen of the pathogen Plasmodium falciparum. Two phase II studies, results were published in December in the New England Journal of Medicine, report of a protection of more than 50 percent of children in Kenya and Tanzania. About 900 children at the age between five and seventeen months received the vaccine RTS,S developed by Glaxo or an anti-rabies inoculation as control. An additional study in Tanzania used the vaccine in combination with routine vaccinations against diphtheria, tetanus, hemophilus influenza, pertussis and polio. Both studies also vary regarding the used auxiliary substances. In the Kenyan-Tanzanian study a new adjuvant increases the antibody titer about ten-fold. Nonetheless the data shows a comparatively good protection against the disease. The fact that the vaccine – compared to prior studies – worked a lot better come as a surprise even to experts, as the malaria specialist Volker Heussler at the Hamburger Bernhard Nocht Institute reports during a meeting with DocCheck. “The comparable efficiency of the two vaccines despite the different adjuvants points towards it that not only antibody- but also a T-cell remitted immunity plays a role in the defense against plasmodia-sporozoits”. “After a development time of more than twenty years still nobody knows exactly how RTS,S works”, says Kevin Marsh, director at the English-Kenyan research center in Kilifi.

The scientists at the Hamburg institute are waiting anxiously for some results of a current study in Ghana. Anyhow, experts like William Collins and John Barnwell at the American CDC hope that the new adjuvant could provide a longer protection than the one to two years achieved so far.

Bacteria against aging mosquitos

The team of Scott O’Neill in Bisbane, Australia describes a strategy of quite a different nature in the penultimate edition of “Science“. Their idea is based on shortening the life span of the mosquitos as a carrier so the parasite cannot develop any more. The Australians managed to transfer a symbiontic bacterium of the drosophila, Wolbachia, to the carrier of the Dengue virus. Since only infected Aedes Aegypti-females pass on their unwanted bacterium guest and the reverse combination produces no viable offspring, the scientists figure out good chances to augment the bacteria in the wild as well. Wolbachia shortens the life span of its host by about half. In a comment published in Science, Andrew Reed and Matthew Thomas speculate: If scientists succeeded in shortening the life span of the Anopheles-flies to three weeks as well, the fly would have just one week to take in the pathogen during a prick on an infected person. Because researchers assess about two weeks as the time the malaria gametocyte takes to develop into sporozoits mature enough for a further progency in humans. Such a “time pressure” could at least strongly stem the plague. But up to now nobody knows whether such hypotheses will also function in Africa.

Why does the malaria pathogen succeed to get around all experiments with vaccines and active ingredients against itself and its carrier? “There is no simple animal model”, says Gerd Pluschke at the Basel Tropical Institute. Just with owl monkeys and apes in which the pathogens proliferate, research can advance only slowly. Most likely a combination of all strategies could lead to the calculations of Gabriela Gomes becoming reality and to giving the tropical countries new hope for chances of future development.

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2 comments:

Heilpraktikerin Elinor Robinow
Heilpraktikerin Elinor Robinow

Anything that helps defeat this terrible infection is welcome!
Keep on trying, some day some effective means will be found.
although resistence will always be a threat.

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Mr William Bradley
Mr William Bradley

A very interesting article that offers some hope that a vaccine might be possible. At the moment , it is very early days and a protection rate will need to be over 80% if vaccinationis going to work.

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