Source: Bernama, Malaysia, 24 September 2008
Kuala Lumpur. Despite rapid advances in medical sciences during the past decades, mosquito-borne diseases like dengue, Japanese encephalitis (JE), 'filiarisis', malaria and chikungunya continue to haunt mankind. This is due to the fact that the mosquito vectors as well as causative agents like bacteria and fungi have developed resistance against the pesticides and anti-microbial drugs.
"Dengue, which has spread across the globe, is caused by the breeding and adaptation of the Aedes aegyptii and Aedes albopictus mosquito."This is the reason why dengue is still rampaging in Asia," Forest Research Institute of Malaysia (FRIM) Dr Nor Azah Mohamad Ali told Bernama here recently. Dr Nor Azah is a senior researcher with medicinal plants programme at FRIM's Forest Biotechnology Division.
According Dr Nor Azah the best move to curb the breeding of the mosquito is to destroy its larva or through the use of insect repellents. "At the moment, the control of the mosquito vectors depends on the chemical-based and synthetic repellents like dimethyl phthalate, malathion and dimethyl-m-toluamide (DEET). She said even though the chemicals are effective, some could be hazardous apart from being ozone-depleting and continuous use could turn the mosquito vectors resistant to insecticides.
Dr Nor Azah suggested the possibility of using herbs and spices, whose essential oils are able to repel insects, be used in insecticides. This is due to the presence of monoterpenoids like limonene, citronellol, geraniol and citronellal that have been reported as having insect repellent properties. "As aroma play an important role towards controlling the insects behaviour, essential oils can be used as insect repellents", she said.
From FRIM's research, a number of essential oils such as Cymbopogon nardus, Litsea eliptica, Melaleuca cajuputi and Cinnamomum spp demonstrate repellent properties against the Aedes agyptii mosquito. She said essential oils from other plants, reported to be able to repel insects are that from geranium (Pelargonium citrosum), sandalwood (Aquilaria malaccensis) and Sweet Basil (Ocimum spp).
"There are other aromatic species that can be found in the Malaysian forest or that cultivated in parks for their medicinal properties and culinary reasons. Essential oils from these species are also preferred by the essential oil industry," said Dr Nor Azah, who has been with FRIM since 1987.
Since the early 1990s, FRIM has carried out research on the potential for their extracts to be used for various purposes. "Our research is focused on the extraction process. We also make trips to the jungle for random sampling of plants that contain essential oils. FRIM's efforts are among the earliest research work on essential oils in Malaysia," she said.
Since 1994, the research centred on the production of essential oils that emit strong aroma. When FRIM set up its medicinal plants division in 1995, the research work is geared towards bioactivity work. Then, dengue was a frequent occurrence, she said.
Dr Nor Azah said the use of various repellents to kill Aedes mosquito could inevitably turn the insect to be resistant to such chemicals. She said the study conducted was on more than 30 plant extracts including that from serai wangi (Cymbopogon nardus), citrus fruits, medang, sandalwood, kemoyang and betel plant.
Further research work is needed on scent-producing plants, which can be utilised for the making of insect repellents and aromatic agents.
She said from studies held at FRIM, it was found that aroma-producing plants like citrus, selasih (Ocimum), serai (Cymbopogon) and medang (Cinnamomum) exhibited their potential in repelling mosquito when tested on Aedes aegyptii via the American Society Testing and Materials (ASTM) standard E951-85.
Dr Nor Azah said the most effective essential oils discovered so far are that from the citrus plants. "Mosquito is repelled by certain aromas from essential oils. Our aim now is to find the essential oils that can kill or knock down this insect," she said.
She said the research conducted at FRIM is to also know more about these therapeutic effects on, among others, the human skin. "All ingredients, no matter how natural they are, would have side effects if excessively used. Essential oils are not ideal for direct use (and) they should be blended in the form of creams or lotions. Dr Nor Azah also cautioned that some essential oils might cause allergies to pregnant women.
Among the success chalked by FRIM on its research over essential oils is the discovery of 'Deesrept' which contains one or a blend of essential oils from the citrus family. "This essential oil can be included in creams and lotions," she said.
FRIM's research showed that this essential oil product is able to repel the mosquito to the extent of killing it," said Dr Nor Azah.
These products could also be used as body sprays or air fresheners, she said, adding that a Bumiputera firm is working on commercialising the product.
Further research is needed to ensure non-toxicity and optimum efficiency of the essential oils. FRIM would carry out more research, as there are still more of the untapped medicinal plants in the country's forests.
Public awareness on alternative products for repelling mosquito is high but there are only few of such products in the market due to limited resources of raw materials, she said. The use of natural herbs as raw products has pushed up the processing costs.
FRIM has set up a sub-station in Maran, Pahang for the cultivation of medicinal herbs like serai wangi for research and commercial purposes. At the same time, FRIM is also taking pro-active measures in maintaining the natural resources. "Our jungles contain numerous herbal treasures that have potential, but if we acquire any species for research, then we will plant it back."
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