Bioensayos de efectividad

1. PUBLIC HEALTH JOURNAL 17/200532
A P P L I C A T I O N & A S S E S S M E N T
Successful knock-down and mortality
A long-lasting insecticidal net (LLIN) should retain its efficacy against malaria
mosquitoes even after 20 washes or more. To confirm this for the
K-O TAB
®
1-2-3 technology, Bayer Environmental Science has carried out an
extended series of biological testing and chemical analysis.
Internal efficacy testing by Bayer Environmental Science
he investigations carried out by
Bayer Environmental Science
are based on the WHO requirements
on mosquito knock-down and
mortality. Mosquito nets treated
with K-O TAB
®
1-2-3 were evaluated
against the mosquito Anopheles
stephensi under laboratory condi-
tions to determine their efficacy after
a series of washes. All the results
refer to 100% polyester mosquito
nets, white and colored, 75 and 100
denier, purchased from a commercial
net supplier. Washing methods and subsequent
bioassays were derived from WHOPES protocols.
Confirming the quality of net treatment
First, all nets were pre-washed in a washing
machine at 30 °C without detergent to remove any
water repelling additives present. Then large nets
(14.25 m
2
) were treated with K-O TAB
®
1-2-3
according to the recommendations by Bayer
Environmental Science (see page 30). To ensure
that the desired amount of deltamethrin is fully
applied, this was checked by an extended series of
chemical analysis, both in-house at Bayer
Environmental Science and at the WHO
Collaborating Centre at the ARC Gembloux,
Belgium. Results showed an average target rate of
deltamethrin of 23.3 mg per m
2
, a value corre-
sponding to the FAO guidelines for
active ingredients. Moreover, an even
distribution of deltamethrin over the
entire surface of the net was also con-
firmed by chemical analysis.
Defined washing procedure
In order to test the wash resistance
and efficacy against Anopheles
stephensi, suitable samples of the
treated nets were washed with Savon
de Marseille, a soap recommended
by WHO. The required amount of soap (usually
2000 mg/liter) was diluted in 2 litres of water at a
temperature of 30 °C in a plastic bucket. Washing
involved placing the net samples in the bucket
with soap solution, mixing it twice and allowing it
to stand for 4 minutes. The washing mix was then
stirred a further six times and allowed to stand
once more for 4 minutes. The net samples were
then squeezed by hand (wearing gloves) and
dipped six times in the washing water, followed by
soaking for a further 2 minutes. The net samples
T
The author:
DR KARIN HORN,
Bayer Environmental
Science, Monheim

2. PUBLIC HEALTH JOURNAL 17/2005 33
A P P L I C A T I O N & A S S E S S M E N T
WASH RESISTANCE
of K-O TAB
®
1-2-3
treated nets meets
WHO criteria for more
than 25 washes and
efficacy against
Anopheles stephensi.
Washing methods
derived from WHOPES
protocols.
Laboratory studies by Bayer Environmental
Science have confirmed the wash resistance
and bio-efficacy of K-O TAB
®
1-2-3 treated
nets against malaria mosquitoes. Additional
trials are still underway to test other net mate-
rials (e.g. polyethylene) as well as different
detergents or detergent quantities.
CONCLUSION
You can find the full report on internal
efficacy testing of K-O TAB®
1-2-3 on
the enclosed Public Health CD-ROM
Summary of wash resistance results with K-O TAB
®
1-2-3
were then rinsed in cold flowing tap water twice
and squeezed to remove excess water. The net
samples were dried flat on aluminium foil for at
least 24 hours until the next washing.
Bioassay according to WHO testing
guidelines
WHO testing guidelines involve exposing adult
mosquitoes to net samples for three minutes, then
returning them to a “clean” tube with food (sugar
water) provided. After 60 minutes, the number of
“knocked down” (but not dead) mosquitoes is
recorded, after 24 hours the number of dead
mosquitoes. WHO has set criteria for efficacy
of a LLIN: mosquito knock-down at 60
minutes greater than or equal to 95%,
and greater than 80% mosquito
mortality after 24 hours.
Unwashed
% %
kd Kill
100 100
kd = mosquito knock down after 60 minutes Kill = mosquito mortality after 24 hours
Convincing results
Bioassay testing of polyester nets treated with
K-O TAB
®
1-2-3 fulfil all of the WHO criteria (see
table). After 25 washes a knock-down rate of
100% was still achieved and mortality after 24
hours was 94%. If less washing detergent was used
than specified by WHOPES, K-O TAB
®
1-2-3
treated nets still met WHO criteria after 30
washes, when the trial was discontinued due to
time constraints.
10 × washed
% %
kd Kill
100 100
15 × washed
% %
kd Kill
100 97
20 × washed
% %
kd Kill
100 97
25 × washed
% %
kd Kill
100 94
Net washed with 2000 mg Savon de Marseille/liter