Wednesday, November 17, 1999 Published at 18:56 GMT
Peppermint oil hits mosquito breeding
Peppermint oil may protect against mosquito bites
An extract of a common herb is being touted as a cheap alternative to existing pesticides in the war against mosquito-borne disease.
Peppermint oil is recommended by fans of alternative medicine to ease symptoms like indigestion, nausea and even to treat colds and flu, reports New Scientist magazine.
However, research by malaria experts suggest that the herb extract can not only repel adult mosquitoes, but kill their larvae before they even hatch.
Some experts say that peppermint oil could become a low-cost and more environmentally sensitive solution to eradicate the insects that carry potentially dangerous diseases such as malaria, filariasis, dengue fever and West Nile virus.
The team from the Malaria Research Centre in Delhi, India, extracted the oil from locally-grown peppermint, then tested it on the larvae of three mosquito species by spreading it in a film on water supplies.
Once the concentration had reached three millilitres per square metre of water, between 85% and 100% of the larvae died within a day, depending on their species.
In addition, volunteers doused in the oil were offered up as bait for mosquitoes, and found to be 85% protected.
The oil was particularly effective against Anopheles culicifacies which is responsible for approximately three-quarters of malaria transmitted in northern India.
Too much peppermint needed
However, a London expert expressed doubt whether their findings could ever translate into a viable pesticide, as, at this dosage, the amount of plant required would be enormous to cover even a small area.
Far lower amounts of existing commercial pesticides would be required, said Christopher Curtis, from the London School of Hygeine and Tropical Medicine.
He said: "You would need tonnes of leaves to treat all the breeding sites around a village."
Malaria is still one of the world's biggest killers, responsible or partly responsible for as many as 2.7 million deaths each year, 90% of which are in tropical Africa.
It is caused by a parasitic organism called plasmodium which is passed on when an infected mosquito bites a human.
Although there are both preventative and curative medicines for the illness, malaria control programmes also focus on the treatment with insecticide of the habitats of malarial mosquitoes close to human settlements.