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   May 30

Herbal repellants that prevent malaria

Mosquitoes have become the most important single group of insects well known for their public health importance, since they spread many tropical and subtropical diseases such as dengue fever, yellow fever, malaria, filariasis and encephalitis. Thus, one of the approaches for control of these mosquito-borne diseases is by killing or preventing mosquitoes from biting human beings.

Herbal products with proven potential as repellants can play an important role in the interruption of the transmission of mosquito-borne diseases. However, the development and use of synthetic organic chemicals with persistent residual action not only overshadowed the use of herbal products against mosquitoes, but also became the major weapon for controlling mosquito populations.

It has also resulted in the development of resistance of mosquito to synthetic insecticides, undesirable effects on non-target organisms and fostered environmental and human health concern. This has necessitated the need for search and development of environmentally safe, biodegradable, low cost, indigenous methods for mosquito control which can be used with minimum care by individuals and communities in specific situations.

Owing to the adverse effects of synthetic insecticides, either used in killing or preventing mosquitoe bites, there has been increasing need to search for natural and environment-friendly insecticides of plant origin as agents of control of vector of malaria parasite.

There are a number of suitable alternatives to using topical pesticides on human skin. These types of products are completely non-toxic, with no side effects, and are just as effective as dangerous chemical pesticides.

Interestingly, over 10 herbs are used as mosquito repellents in Ibadan. These are neem (dongoyaro), lemon grass leaves, basil leaves, Ageratum conyzoides (goatweed leaves), Annona squamosa (sweetsop leaves) and Hyptis suaveolens(bush tea leaves).

Others are Tridax procumbens (coat buttons leaves), Citrus sinensis (orange fruit peels), Lantana camara (wild sage leaves) and Solanum nigrum (black night shade leaves).

Researchers in a study that compared the effectiveness of these plants as mosquito repellents indicated that seven of these plant extracts showed promising repellent activity against mosquitoes. These are lemon grass leaves; sweetsop leaves; orange fruit peels; black night shade leaves; coat buttons leaves and neem.

While low repellency was observed in basil leaves, goatweed leaves and bush tea leaves, complete protection was observed within 30 minutes of application of hexane and methanol extracts of lemon grass leaves and wild sage leaves.

The 2010 study, published in the Journal of Applied Biosciences and entitled “Comparative effectiveness of ethnobotanical mosquito repellents used in Ibadan” was carried out by Egunyomi A, Gbadamosi I.T. and Osiname K.O., all from the University of Ibadan.

The researchers suggested that these plants can be used alone or combined for effective protection against mosquitoes. In addition, they can also be used for control of mosquito breeding under integrated disease vector control programme in various situations.

Moreover, Nigeria Natural Medicine Development Agency, taking advantage of traditional knowledge of plants with insect repellent properties also developed a mosquito repellent cream from eucalyptus oil, neem oil, sweet basil oil, lemon grass oil, Hyptissuaveolens, palm kernel oil and shea butter.

Moreover, sweet basil oils have comparable to a commercial wipe containing synthetic repellents. Its oil ensures bite protection for two to three hours at all the concentrations tested after application of the oil.

Previously, researchers at the Obafemi Awolowo University, Ile-Ife said Piper guineense and Xylopia aethiopica fruits oils in liquid paraffin can be used as mosquito repellents. Xylopia aethiopica is guinea or african pepper.

The study, documented that eucalyptus oil had a similar effectiveness to X.aethiopica and P, guineense in warding off mosquitoes.

P. guineense and X. aethiopica oils showed complete protection from mosquito bite for two hours at 35 per cent(v/v) and 30 per cent respectively. The activity of eucalyptus oil (positive control), a commercial repellent, at 30 per cent was only able to protect for two hours. Both oils used could be applied as repellents where protection from mosquito bite is sought for, over a short period of time.

Its repellence is dependent on both the concentration of oil in solution and time after application. Repellence increased with concentration and also decreased with time after application.

“No significant protection could be obtained when using the oil at below 15 per cent and 20 per cent for X. aethiopica and P. guineense respectively,” the researchers pointed out.

Protection from mosquito bites could not be sustained for a longer time due to evaporation of the oils from the skin shortly after application. In order to achieve a longer protection using any of the oils, it may be necessary therefore to consider reapplication after an expiration of two hours of the first use.

In many communities at Ogbaru Local Government Area, Anambra State orange peels are placed on top of lighted lamps,. They put scent leaves, lemon grass or bush tea leaves on the windows and corners of their rooms.

According to a study titled “Formulation of an effective mosquito-repellent topical product from lemon grass oil”, published recently by the Department of Pharmaceutics, Obafemi Awolowo University, Ile-Ife, extracts of lemon grass cannot only bring relief in malaria fever, but can repel mosquitoes.

The team of researchers: Oyedele A.O, Gbolade A.A, Sosan M.B, Adewoyin F.B, Soyelu O.L and Orafidiya O.O evaluated ointment and cream formulations of lemon grass oil in different classes of base and the oil in liquid paraffin solution for mosquito repelling property in a topical application.

The one per cent v/v solution and 15 per cent v/w cream and ointment preparations of the oil exhibited not more than 50 per cent repelling lasting two to three hours, which may be attributed to citral, a major oil constituent. Its effectiveness was comparable to that of a commercial mosquito repellent.

Meanwhile, several potent anti-malaria cocktails from local plants have been developed. A typical cocktail consists of leaves of Morinda lucida, Nauclea latifolia, lemon grass, male pawpaw, Moringa oleifera, stem back of Mango tree, bitter kola, and guava tree.

Researchers have compared the efficacy of crude aqueous extract of Mango, pawpaw and sulphadoxine pyrimethamine on mice infested with malaria parasite in vivo.

Uhegbu, F. O., Elekwa, I., and Ukoha, C. of the Department of Biochemistry, Faculty of Biological and Physical Sciences, Abia State University, Uturu, investigated the comparative efficacy of sulfadoxine-pyrimethamine (Maloxine) and leaf extracts of Mangifera indica (mango) and Carica papaya (paw-paw) in Plasmodium berghei-infected mice.

According to the study published in Global Journal of Pure and Applied Sciences, Maloxine had the highest efficacy, reducing the parasite count after six days of treatment. However, a combination of the two leaf extracts exhibited a higher antimalarial efficacy than the separate leaf extracts.

Source: Nigerian Tribune

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