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
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 achieved.by the collaborative efforts
of entomologicsts, chemists and other experts.
The ever on-going process of continuous improvement and production
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
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..