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Transfluthrin. Insecticide used in the "Repellent Lamp"
used for personal protection against mosquitoes in Dar es Salaam, Tanzania

http://www.lshtm.ac.uk/itd/units/dcvbu/research/lamptext.htm

London School of Hygiene & Tropical Medicine, Keppel Street, London WC1E 7HT, UK. 

The 'Repellent Lamp' 

The 'repellent lamp': using a modified traditional kerosene lamp for personal protection against mosquitoes in Dar es Salaam, Tanzania

1. What is it for?

The Repellent Lamp works as a space repellent. It is intended to act as a complement to a treated net, ie to protect against biting during the evening, before going to sleep under a net.

Many people currently use mosquito coils for this purpose. Entomologists and users both recognise that coils are not very effective, give off an unpleasant smell, and can increase the risk of respiratory disease.

An alternative is the use of 'vapourising mats'. These are little blue cardboard tablets which, when heated in a small device powered by mains electricity, give off pyrethroid vapour. These are more effective but much more expensive than coils, and can only be used where mains electricity is available.

2. What is it?

All the components except for the insecticide were bought locally.

In Tanzania, lamps of this type are the main source of light at night for most people. Manufactured hurricane lamps and candles are also available, but are more expensive.

Technical grade transfluthrin was kindly donated by Bayer. Transfluthrin is a volatile pyrethroid, as is the more widely known bio-allethrin. These compounds are similar to the pyrethroids used on nets, but evaporate at much lower temperatures. They are the active ingredient in the vapourising mats mentioned above, and in some brands of coil.

3. How does it work?

The insecticide evaporates best at temperatures of 150-200 oC. At the much higher temperatures of the flame, it is destroyed, so putting the insecticide into the kerosene fuel does not work. However, by adjusting the height of the legs of the tripod (figure 1), it was possible to keep the vegetable oil in the small tin within the target range. The oil ensures that the insecticide is heated uniformly.

4. Components of the Repellent Lamp

(i) The lamp.

Made by local smiths from scrap metal and solder. The base is made from a tin, with a metal chimney and flame above. Used with string wick and kerosene fuel.

(ii) The tripod.

A small tomato puree tin with no lid, supported above the flame by a platform of welded wire rod with three legs.

(iii) The insecticide.

A thin layer (5ml) of cooking oil containing 0.1% or 0.5% of the volatile pyrethroid transfluthrin.

5. Isn't there a catch...?

Yes there is. If the flame is allowed to become very long and sooty, so that it touches the bottom of the tin, then soot can build up on the base of the tin. Eventually, the soot itself (not the oil) can start to burn. This does not happen rapidly or violently, but it does create an additional and probably unnecessary fire hazard. A design must be found that avoids or minimises this problem.

6. Conclusions

In terms of cost-effectiveness, the lamp appears to be comparable with a coil. At the dosages used here, the factory cost of the insecticide is unlikely to exceed 1 US cent.

More technical evolution is required. Is the lamp really as 'appropriate' as it may appear? Further technical modifications are no doubt possible to make it easier and safer to use.

Does it protect against malaria as well as mosquitoes? Epidemiological evaluation will be necessary to justify substantial public health investment, but perhaps not for further commercial development.

7. Update

Here are pictures of the Repellent Lamp Prototype Mark II. It has yet to be tried in practice, but it looks pretty good. We hope that by adjusting the positioning of the wires, we can prevent the chimney and wick from getting too close to the bottom of the tomato tin. This should prevent the build-up of soot on the underside of the tin, and thus eliminate the fire hazard mentioned above in section 5.

For more information, contact Jo Lines or Helen Pates.

This page was last updated on 23 November 2000 by Jane Wooders

 

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