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PYRET
IM PRE(
MOSCW
Protection from Mosquitoes and Malaria
MALARIA RESEARCH CENTRE
(Indian Council of Medical Research)
22, Sham Nath Marg :':;
Delhi-110 054
Malaria control becomes nearly impossible in certain
areas. Such situations are usually caused by the
following factors occurring singly or in combination:
•
High rainfall with water logging
•
Innumerable mosquito breeding sites with enor
mous surface areas
o
High vector densities and continuous man-vec
tor contact
o
Areas refractory to spraying
•
Tribal dominated, backward areas, forested and
difficult terrain.
Rivers, streams, seepages, high water table, noncooperative communities and poor health/communication facilities further exacerbate the problem. In
such situations malaria control could be achieved by
certain personal protection methods. One of the most
successful method is the use of mosquito nets
(bednets).
IMPREGNATED MOSQUITO NETS
Since time immemorial mosquito nets have been used
for protection from mosquitoes, malaria and nuisance
insects. However, they do not provide sufficient pro
tection because hungry mosquitoes may rest on the
mosquito net and bite on the first available opportu
nity. This could either be due to damaged or im
proper tucking of mosquito net. Mosquitoes may
bite when trapped inside the mosquito net. Those
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outside may also bite, if any part of the body comes
in contact with the mosquito net. There are some
studies indicating nets being a favourable site for
female mosquitoes to rest.
Attempts to treat mosquito nets with repellents to
ward off mosquitoes failed. However, treatment (im
pregnation) of mosquito nets with synthetic pyrethroid
with residual action removes the problem of plain
mosquito nets and these are ideally suited to pre
vent man-mosquito contact.
PYRETHROIDS
Pyrethroids are synthetic analogues of natural pyrethrins derived from the plant Chrysanthemum
cinerariifolium. These include permethrin, cyfluthrin,
deltamethrin, lambdacyhalothrin etc. Pyrethroids suit
able for impregnating mosquito nets are available as
emulsifiable concentrates (EC), oil-in-water emulsion
(EW) and flow. Impregnation with wettable powder
(WP) formulation is not accepted by the users due to
flaking of powder during regular use.
PROPERTIES OF PYRETHROIDS
•
Cause fast knock down of mosauitoes on con
tact.
•
Effective at low dosage on mosquito nets com
pared to conventional insecticides.
•
Have long residual action (single impregnation
lasts for more than 6 months if the mosquito
net is not washed).
2
•
Have low mammalian toxicity; absorption by skin
is very poor.
•
Are odourless and do not stain clothing.
•
Have broad spectrum activity on headlice, cock
roaches, bedbugs, ants etc.
•
Easy to make emulsion of EC or EW formulation
with water for impregnation. Flowable formula
tion mixes well with water.
MOSQUITO NET SPECIFICATION
Mosquito nets of varying colour made of nylon or
cotton fibre are suitable. Mosquito nets should be
large enough to cover a bed properly. For a single
bed mosquito net of 10 m2 and for a double bed of
15 m2 would be appropriate. Approximately, 10-15
cm cotton cloth should be properly hemmed with the
net for tucking under the mattress or bed. Rectangu
lar mosquito nets are generally preferred in India,
however, mosquito nets of any other shape could
also be used.
For proper ventilation mesh size of about 3 to 4 mm
(i.e., 6-8 holes per linear inch or 3-4 holes per linear
cm) is recommended.
IMPREGNATION PROCEDURE
Impregnation of mosquito net with pyrethroid is
achieved in three steps. They are:
Step X
The surface area of the net (Fig. 1) is determined by
3
•Height
Fig. 1:
Surface area of an appropriate mosquito
net S.A.= (a+b)+c
using the following formula:
Surface area
Where,
=
2 (a+b)+c
a
length x height
b
height x width
c
length x width
The amount of formulation of insecticide required for
target dose of 25 mg/m2 is calculated as:
Weight required (gm) = Surface area in m2 x 0.025
4
The volume of formulation required is determined by:
Volume =
required
Weight (gm) x 100
Per cent formulation of insecticide (ml)
For example, to impregnate a mosquito net of 10 m2
using 2.5% EC formulation the volume of formulation
required would be:
(10 X 0.025) x 100
--------------------------2.5
= 10 ml
Once the volume of insecticide required for one mos
quito net is standardized, the volume of water just
sufficient for completely soaking the mosquito net
without any dripping is determined by trial and error.
Approximately a nylon mosquito net of 10 m2 takes
about 350 ml water. Always use cold water for im
pregnation.
Step 2
The insecticide formulation and water (as per vol
umes determined) are mixed thoroughly in a wide
plastic basin. Hand gloves should be used, while
handling pyrethroid. The insecticide emulsion is ap
plied thoroughly to the mosquito net by repeated rub
bing and squeezing to distribute the emulsion evenly
to all parts of the net. Netting part should be soaked
first, followed by cotton hem.
Step 3
The mosquito nets thus impregnated with insecticide
are spread on a non-absorbent surface (such as a
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plastic groundsheet) and allowed to become semi
dry. Semi-dry mosquito nets are then hung on a wire
and allowed to dry completely. Mosquito nets could
also be dried on cots or leaf mats. Both stages of
drying should be accomplished in shade. One im
pregnation will last for more than six months, if the
mosquito net is not washed. If washed before 6
months, reimpregnation is advisable for better re
sults.
Recommended dosages for Impregnation
Net
size
(sq m)
Target dose
(mg/sq m)
Volume
of formuulation (ml)
2.5%
10
15
25
25
10
15
5%
10
15
10
15
25
25
50
50
5
7.5
10
15
Concentration
of formulation
PRECAUTIONS
After impregnation hands and face should be washed
thoroughly with soap and water. In some cases con
tact with emulsion during impregnation may result in
transient mucosal irritation. Recommendations on con
tainer labels or sachets, if any, must be adhered to.
Use of hand gloves is essential during impregnation.
In case of non-availability of gloves, polythene bags
could also be used.
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RESULTS OF BEDNET TRIALS
Assam
The impact of mosquito nets treated with deltamethrin
@ 25 mg/m2, untreated nets and no nets (control) is
shown in Fig. 2. Results clearly show that treated nets
were very effective in malaria control. Untreated nets
provided partial protection and there was no protec
tion in areas without mosquito nets.
Fig. 2 : Impact of deltamethrin treated mosquito nets
on malaria incidence in Sonapur PHC, Assam
7
25
Months
Fig. 3: Impact of cyfluthrin treated mosquito nets
on the density of malaria vector An. fluviatilis
in mining settlement in Orissa
30
01-------------------------------------------------------------------------------------------------MJ JASONDJ FMAMJ JASONDJ FMA
92
|
93
|
94
Months
Fig.4 : Impact of cyfluthrin treated mosquito nets on
malaria incidence in the mining settlements
in Orissa
8
Orissa
In the settlements of iron ore mines in District
Sundargarh, Orissa introduction of mosquito nets im
pregnated with cyfluthrin @ 50 mg/m2 led to signifi
cant decline in the density of malaria vector Anoph
eles fluviatilis (Fig. 3) and malaria incidence (Fig. 4).
ECONOMIC CONSIDERATIONS
Cost and availability of pyrethroids: Ny
lon mosquito nets are easily available in most of the
towns/cities in India. A single size mosquito net
costs about Rs. 75. Insecticide application and dis
tribution cost may be estimated at Rs. 15 per year.
Thus, the cost of treated mosquito net may be esti
mated at Rs. 90.
TARGET POPULATION/GROUPS
Identification of target groups who will benefit most
from this method of personal protection is absolutely
necessary. Some ideal target groups are:
•
Tribal communities in backward areas whose tra
ditional clothing maximises vector contact.
•
Shifting ("Jhoom”) cultivators who camp in the
fields.
•
Areas with high malaria vector density and con
tinuous man-vector contact and where indoor
spraying is not effective.
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•
Problem areas which have extensive breeding
sites/resistant vector/drug resistant malignant
malaria.
•
Inaccessible areas such as hills/forest with poor
communication facilities.
•
Highly vulnerable groups namely pregnant
women, infants, migrants from non-malarious ar
eas to malarious areas (e.g. tourists), labour
congregations, industries, mines, army installa
tion etc. in forest.
FIELD EXTENSION AND EDUCATIONAL
SUPPORT
Better compliance with mosquito net usage at com
munity level would increase their effectiveness. This
can be achieved by education/extension activities
along with distribution of mosquito nets. Users/
target groups should be prepared to accept mosquito
nets as a way of life. The main discussion points
with regard to use of mosquito nets are:
•
Always sleep under a mosquito net.
•
Make sure that all members of the family, espe
cially children and expectant mothers, sleep un
der the net.
•
Tie the net properly, preferably with cane poles
or with strings on walls. If the net is properly
stretched air flow is maintained and the user is
more comfortable.
•
Tuck the net properly under the mattress or bed
from all sides.
10
o
Use a larger net to avoid contact of exposed
body parts with the net.
o
Take good care of your net. If it gets torn,
mend it carefully so that no holes are left.
o
The pyrethroid is effective for more than 6
months, but washing removes it. Therefore, avoid
washing as far as possible. If washing is inevi
table treat the net again.
Educating communities is very important for the suc
cessful introduction of mosquito nets in any area.
But once introduced they are habit forming and re
peated persuasion is not required. Group meetings,
video shows, lectures in local schools, colleges and
door-to-door contact programme will enhance commu
nication with the people and ensure community par
ticipation.
ADVANTAGES
Mosquito nets are cost-effective, socially acceptable,
free from health hazards and offer simple solution to
an intractable problem. Impregantion with pyrethroid
ensures greater effectiveness because of rapid knock
down of all insects that come in contact. Since
impregnation is long lasting and socially acceptable
their effectiveness is ensured.
The method is environment-friendly as it obviates un
productive spraying. Since man-vector contact is great
est indoors, during night mosquito nets are a situa
tion-specific remedy for the same.
oco>*’
U603S
A nylon mosquito net lasts for five to seven years.
The recurring cost of insecticide impregnation is about
Rs. 7-10. So, protection against mosquitoes is pro
vided for Rs. 15-20 per annum. This is almost negli
gible when compared to the cost of repellents.
Thus the use of impregnated mosquito nets for ma
laria control is highly cost-effective, socially accept
able, sustainable and free from health hazards.
Printed by Akhasdeep Printers New Delhi-2
MRC Technical Information Series No 002/96
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