Features

Now Neem takes on malaria

K. S. Jayaraman

doi:10.1038/nindia.2009.302 Published online 29 September 2009

© WHO

Indian researchers have found more merits of the ubiquitous neem tree (Azadirachta indica) — it is a potential resource for new insecticides to replace chemicals currently used to control mosquito-borne diseases, especially malaria.

Traditionally, Indians use home-made neem preparations as health products and for pest control. Now scientists at the Vector Control Research Centre (VCRC) in Puduchery have evidence that azadirachtin, the bioactive substance in neem can control mosquitos1.

The VCRC scientists have evaluated a commercially available product called 'NeemAzal', derived from neem seed kernels, that contains 1.2 per cent emulsifiable concentrate of azadirachtin. The scientists studied its effect on the larval stage of Anopheles stephensi, Culex quinquefasciatus and Aedes aegypti — vectors responsible for spreading malaria, filariasis and dengue respectively.

The results were highly encouraging, according to their report. Less than 1 part per million (ppm) of the product, added to larval basins, was adequate to interfere with larval development. "It was clear that the formulation disrupted insect growth by affecting different molting stages of the larva thereby inhibiting emergence of adult mosquitoes," the scientists report.

"Our results indicated that because of its emergence inhibition activity, NeemAzal could be a promising candidate for use in integrated vector management programmes replacing chemical insecticides," they said.

"Such validation studies provide a rational basis for integrated disease control exploiting both, modern science and traditional medicine knowledge," says an accompanying commentary2 by a group of Italian public health specialists. "As neem trees are very common in most countries with mosquito-borne diseases, neem based larvicides can be produced locally."

Currently, malaria control strategies target adult mosquitoes using synthetic chemical agents for treating bed nets and indoor residual spraying. "However, due to drawbacks including lack of selectivity, environmental contamination, and emergence and spread of vector resistance, development of natural products for vector control has been our priority," M. Kalyanasundaram, one of the authors told Nature India.

Among the three species tested, the malaria vector A. stephensi was highly susceptible to NeemAzal. The formulation produced an overall mortality or inhibition of emergence of 90 per cent at 0.046, 0.208 and 0.866 ppm in A. stephensi, C. quinquefasciatus and A. aegypti, respectively. Most of the mortality was in larval as well as in pupal stage and only a very few were dead at adult stage.

The advantage of using neem formulation as larvicde is that it is of plant origin, is very selective, and safe for non-target organisms, Kalyanasundaram said. "We however have to carry out a field study before we can recommend this for introduction into the national vector control programme."

According to the VCRC team, there is scope for further improvement to the present formulation to produce higher larvicidal activity at lower concentration.

One drawback of azadirachtin is it can be degraded by sunlight. However, by adding suitable surfactants or stabilisers the formulation can be prevented from photo degradation. Therefore, in a suitable formulation, azadirachtin could be adequately stable in water retaining its bioactivity for as long as 100 days in water, the researchers said.

K.Gunasekaran, the first author of the paper says the cost factor will be worked out after the phase-II trial. He is hopeful neem formulations, currently used only in the agricultural sector, will enter the public health area and potentially replace environmentaly unsafe chemical agents. "When this happens, companies that currently supply synthetic agents for mosquito control programme may be forced to source their products from neem."


References

  1. Gunasekaran, K. et al. Larvicidal & emergence inhibitory activities of NeemAzal T/S 1.2 per cent EC against vectors of malaria, filariasis & dengue. Indian J. Med. Res. 130, 138-145 (2009)
  2. Habluetzel, A. et al. Azadirachta indica as a public health tool for the control of malaria &other vector-borne diseases. Indian J. Med. Res. 130, 112-114 (2009)