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Cashew nut by-product may help cut sleeping sickness
  • Cashew nut by-product may help cut sleeping sickness

Copyright: Sanjit Das / Panos

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  • More than 300,000 tonnes of cashew nut shell liquid is produced each year

  • A new method can turn this into chemicals that lure tsetse flies to traps

  • One limitation is the method’s dependence on an expensive Palladium catalyst

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A new method for making chemicals that lure tsetse flies to traps has been developed. It uses a cheap by-product from the cashew nut industry as its starting material, so the discovery may mean the flies — which carry sleeping sickness (also known as African trypanosomiasis) — can be trapped at a lower cost.

The method, published in Green Chemistry last month, could offer a sustainable and more-affordable way to make two ‘attractant’ chemicals: 3-ethylphenol and 3-propylphenol.

Many existing odour attractants are prohibitively expensive and not widely available in large quantities. It is possible to use buffalo urine, which naturally contains chemicals that attract the flies, as a substitute — though this has the downside of smelling rather unpleasant.

Because the new method produces the attractants from cashew nut oil starting material, it may mean African countries could produce the chemicals locally. Cashew nut producers, which are widespread in Sub-Saharan African countries including Côte d’Ivoire, Nigeria and Tanzania, generate more than 300,000 tonnes of this waste product every year.

The liquid contains the chemical cardanol, which can be used to make both 3-propylphenol and 3-ethylphenol, through chemical processes developed by Lukas Goossen, a chemist at the University of Kaiserslautern in Germany who jointly led the research.

David Cole-Hamilton, a chemist at the University of St Andrews, United Kingdom, who also led the research, tells SciDev.Net that the resulting attractant can be coated on a plastic sheet or similar surface, along with an ordinary insecticide. “The attractant lures the insects to the sheet where they are poisoned,” he says.

Cole-Hamilton says the team was anxious to avoid using farmland to produce the raw materials for chemical production. This would put effectively food production and insect control in competition. “For this reason, we targeted waste products from food or other production processes,” he says.

The new process to make the attractants from cashew nut liquid is cheaper than existing methods using synthetic compounds. Yet it involves using small quantities of an expensive Palladium-based catalyst, so it the attractants would still end up too expensive for most individuals to buy, Cole Hamilton thinks.

“A whole village might be able to [collectively buy them], particularly if there were a government or international subsidy,” he says.

However, there may be a solution to this problem, he says. One other product from the process his team has developed is 1-octene, a chemical used to make polythene. “World demand for 1-octene is 600,000 tonnes [a year] and it sells at US$2 per kilogram so the profit from this product could be used to reduce the cost of the attractant,” he says.

Andrew Jonathan Nok, a biochemist at Ahmadu Bello University, Nigeria, and one of the country’s leading sleeping sickness researchers, says the work is commendable.

But, he adds, that advances in trapping flies are unlikely to lead to the elimination of sleeping sickness in themselves because tsetse flies may learn to ignore the attractants.

Nok believes drug and vaccine development remain the best paths for tackling the disease.

Link to full paper in Green Chemistry


References

Green Chemistry doi: 10.1039/C4GC01269K (2014)
 
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