Drop down menu
Permanet story

Development of insecticide coated polyester bednet

The development of the long lasting insecticidal net (LLIN)Permanet® is a story of cross-scientific cooperation and a rare-business sentiment.
We feel due credit has been given to other parties involved in the development of Permanet®.
Intelligent Insect Control are no longer in cooperation with VEstergaard-Frandsen. Inquiries regarding Permanet® should be directed at them. Inquiries regarding the ongoing improvements in the control of vector-borne diseases are gladly received and debated. please see contact page

A mosquitonet impregnated with an insectide/ reppellent was first marketed by Sumitomo but to an audience of mainly wealthy Japaneese businessmen who travlled abroad. Although widely used today as a means of protection against vector borne diseases the net was for many years priced at a level that did not allow for use in emergency relief and by donor organisations. SiamDutch had also concieved an impregnated net at an even earlier stage but without said long lasting inescticidal properties.

Dipping nets were used - and still -are but suffered drawbacks in the practical procedure of re-treatment; they rarely were.

Sociological problems were identified in studies showing lack of understanding of the importance of re-treatment.

Efficacy of treated nets was proven by a WHO study but re-dipped remained a less than perfect solution due to their inheirent design flaw; they need re-treatment.

A cheaper factory-impregnated mosquito net was identified as a viable solution and calls were made to companies in relevant industries.

A small Danish company was the only participant to report themselves willing to undertake the development of a factory impregnated net.

Intelligent Insect Control was formed and the development joint-effort was underway.

Knowledge is collected from related industries in order to arrive at a solution

Production facility is setup in cooperation with a manufacturer in VIetnam and Danish foreign organisation. Production is unstable and results vary too greatly for market launch.

Good enough results finally the collaborative efforts of entomologicsts, chemists and other experts.

The ever on-going process of continuous improvement and production upscaling commences.

Permanet® is recognised as the best impregnated mosquito net available and recievesWHO blue ribbon - seal of quality.

Why do impregnated net work in areas of mosquito resistance and what are their limits?

In1998 a colleague of Ole Skovmand returned to our laboratory of mosquito control at Orstom in Montpellier, southern France, telling about a frustrating field test he had participated in. The program concerned testing of impregnated mosquito nets in a malaria infected area of Cameroun. “It works perfectly”, he said, “see how mosquito population declines and malaria cases dwindle in the first year”, showing tables and graphs of the village and the mosquito and malaria data. Then in the second year, data were not so good, nets were not so effective and inhabitants less motivated to keep them well impregnated. “Once the scientists have left and the inhabitants have to organise the net dipping themselves and buy the insecticides, it will fall apart !” This was a frustration he shared with many other biological, medical and social scientists involved in similar programs.

At the same time,we received a more positive report from East Africa where British and American scientists had organised village groups for collecting nets for dipping and later redipping in insecticide. Ole Skovmand wrote a mail to one of the scientists, congratulating him with this success, and he wrote back, that the report, though newly published, was outdated. In this program, they had organised village committees that collected money from the net-users and these money should then be spent on buying new insecticides for dipping the net after washing. Unfortunately, the guy sent to town with the money for buying insecticides, never returned to the village. Still, the program report was very interesting, since it revealed the cost structure of the program. When ongoing, most costs went to motivating people to use nets, to have the nets reimpregnated every 6 months and in this case to make the village committee for gathering money and buy insecticides for the reimpregnations. Another large study in The Gambia ran by their Ministry of Health showed high participation in a program as long as the government paid for it, and once village inhabitants had to pay for the redipping service themselves, effective impregnation fell to 5 %. The same story was repeated in country after country.

At the same time, WHO had organised very big field trials of impregnated bednets in 3 parts of Africa including hundreds of villages and they all concluded that as long as the bednets were effectively used and well impregnated, they consisted a very effective tool against malaria reducing children overall mortality with 25-30 % and malaria identified, serious cases with 50-60 %. Basically, the tool as a concept was good but the way it was made was not.

Clearly, what was needed was another approach and discussions were raised with Pierre Guillet, who headed our laboratory, to cut out away all these problems and extra costs by replacing the local dip and redip procedures by nets that were factory impregnated and could resist washing, since it was the washing of nets that ended their effect by washing off the insecticides in the process.
Guillet organized a meeting in Montpellier with many people from the industry and research: net producers, textile research institutes, pesticide companies and malaria researchers. Most of them said it was a good idea, but not doable, while a few said they would work on it. One of these companies actually already worked on the idea and had hired two American engineers, but so far nothing had come out of it.
A small Danish company Vestergaard Frandsen had a visionary director of product development, Torben Vestergaard-Frandsen, had identified and via talks with their scientific network arrived at the same conclusion. However, their efforst had up to this point not yielded any viable results and their relationship with the American devopers they had contracted was strained.
Since Ole Skovmand worked in the laboratory in France where this meeting was organised, he was asked to organise tests of the products that the Americans were supposed to develop. Since they never arrived at a stage where a product could be tested the assignment became to develop a solution.

This was the beginning of a year long co-operation between Intelligent Insect Control and this slightly bigger (now much bigger) Danish company, Vestergaard-Frandsen A/S (now re-located to Switzerland).

The first year of the project was oine learning, testing and unlearning; the foundation laid by the previous development-team contained more dead-ends than solid leads. Instead companies in the polymers and dye industries were contacted to learn about solutions to problems similar to the one we were looking at. After about a year we finally arrived at process with which nets in one impregnation process could be impregnated with insecticide and with chemicals that protected against washing off. Laboratory data said it resisted 27 washes which is much more than any net in a poor area of Africa will ever be exposed to. Then we set that in production and Ole Skovmand went to Vietnam to set up production procedures in a factory selected by the Danish company. This was done support from Danida’s private sector program.

The factory was known for making good nets, which meant a good sewing quality. They had never tried to impregnate before, and only had an old machine they used for heat fixing the net so it does not shrink on washes. I knew from the laboratory that temperature during the drying process was critical and on this machine, temperature regulation consisted in opening some doors to cool down or start electric fans with a glowing net in front to heat up. Results of course were not very predictable, and it took a year of rebuilding and some reformulations to get a more stable product. That created some frustrations among customers and scientists testing the nets where some were lucky to get good nets, and some where not and their reports were of course accordingly.

There was a lot of learning down the road about demands to the yarns the nets were made of, processes before and after knitting, before and during impregnation and how to handle workers safety when handling so many nets.
It took nearly another year before all this was in place. Two quality control laboratories were established at the factory, one based on mosquito testing and one on chemical analysis. Doing this, responses on quality came much faster and with a good team of entomologists hired from the local malaria institute and very good chemists, new data and data analysis were obtained. That means that to-day, predictive test on net performance and not only the simple concentration of insecticide can be made. The factory expanded and purchased more modern equipment for the production. Somewhere in this development when a special problem in the impregnation process was solved, a line was drawn in the sand knowing that now the product was sufficient stable so results of field tests were predictable.
This was confirmed in tests surveyed by WHO, the World health Organisation. Large test organised by CDC (the American health organisation working with tropical diseases) told that the nets were far superior to dipped nets and also to the only other net that had good a blue ribbon from WHO as effective. It could be used right after washing, it did not need any heat treatment or the like to be reactivated, it really was a wash-and-go formulation that worked.

What are the limits for these nets, because there are always limits. Most entomologists working with insecticides will say: resistance. When mosquitoes already are resistant or become so because of intensive net use, nets will fail.

Permanet® is impregnated with deltamethrin and deltamethrin is in the group of insecticides called pyrethroids. These have been used for mosquito control and bednets for 20 years, but they are also used in agriculture for instance to spray tobacco, cotton and tomatoes. These plants are all bothered by a species that soon is called tomato worm, then cotton budworm, then other names, but it really is Helicoverpa armigera (zea in USA), and it is heavily sprayed all over the globe and resistant to many insecticides, so high dosages are applied. In dry Africa, these plants also needs a lot of water to grow, so people arrange for (overrisling) and that leaves puddles here and there. Fine for mosquito larvae of the malaria mosquito Anopheles gambiae, the worst vector (transmitter) of malaria in the world. But of course, with insecticides in the puddles, there is a high selection pressure for resistance against insecticides, and a fine correlation is found in Africa in areas with intensive agriculture and resistance of Anopheles to pyrethroids. So, Permanet® should not work in these areas - but it does ! Larvae resistance is not fully carried over to adults, and the type of resistance that mostly has developed is an incomplete target resistance. It works the way that mosquitoes can tolerate more insecticide than normal, but the adult also feel the insecticide less. Normally, pyrethroids are irritating on contact, so sitting shortly on a net, the mosquitoes feel the insecticide and leave (which the larvae cannot, of course, so if not resistant, it dies). Since the reduced feeling of irritancy and the toxicity goes hand in hand, the adult mosquito eager to find a hole in the bed net, touch the net too much - and dies. (well, since I wrote this some months ago, I now know that they may actually be killed once they enter the room and even they never touch the net – results that I will present in Washington in December from a NIH project in Kenya).
Other populations of insects have resistance mechanism based on breaking down the insecticide while having normal contact irritancy, but this type of resistance is so far not common among malaria mosquitoes, so the tool is still effective.

Therefore, Permanet® and Olyset® net became very important tools in the global fight against malaria. In West Africa, sleeping under a bednet that works, increase the survival of children under 6 years age from 3 out of 5 to 4 out of 5 plus it makes life better for many more.

This is not a bad feeling and a nice outcome of this co-operation.We hope to engage ourselves in new partnerships and project ventures that will bring innovative and better solutions to people suffering under the burden of vector borne diseases..

Last Edited: Dec-17-2008


Intelligent Insect Control