Evaluation of KOTab 123: a washresistant

1
Evaluation of KO-Tab 1-2-3 a wash-resistant
dip-it-yourself insecticide formulation for
long-lasting treatment of mosquito nets Alison
Yates, Raphael NGuessan, Harparkash Kaur, Martin
Akogbéto, Mark Rowland London School of Hygiene
and Tropical Medicine, UK Centre de Recherche
Entomologique de Cotonou, Benin
Background Conventional insecticide treated nets
(ITN) need to be retreated with insecticide after
2-3 washes or about once a year. This is a major
constraint on the sustained effectiveness of
individual nets. The majority of nets in use were
treated only once, on receipt, or never
treated. Bayer Environmental Sciences (BES) has
developed a long-lasting insecticidal
formulation, KO-Tab 1-2-3, which raises the
prospect of converting conventional nets into
wash-resistant insecticidal nets in the
home. LSHTM evaluated a series of polyester nets
treated with KO-Tab 1-2-3, two additional
long-lasting formulations produced by BES, a
conventional formulation of deltamethrin (KO-Tab)
and a PermaNet long-lasting net.

Three-minute exposure bioassays in cylinders
There was no loss of biological efficacy even
after 30 washes for any of the long-lasting
treatments (Fig 2). For the conventional
deltamethrin treatment there was survival after 5
washes. There was some mortality even after 30
washes compared to untreated nets, despite
negligible amounts of deltamethrin detected.
Methods Preparation Test nets were treated by
hand and laid flat for drying. Samples were
washed 5, 10, 20 or 30 times in 2 g/litre soap
solution using the standard WHO shaker bath
method.
Median time to knockdown (MTKD) bioassays Using
the netting ball method, time was recorded for
the median mosquito (6th out of 11) to be knocked
down by the insecticide.
Figure 2. Three-minute exposure bioassays
mortality after 24h
Median time to knockdown (MTKD) increases as
insecticide is removed by washing (Fig 3). Over
30 washes MTKD increased by 628 sec for KO-Tab,
by 181 sec for KO-Tab 1-2-3, by 163 sec for
BES903, and by 52 sec for PermaNet. MTKD is
correlated with the amount of deltamethrin
present on the net (Fig 4).
Three-minute exposure bioassays WHO cylinder
test kits lined with netting were used as
exposure chambers. Mortality was scored after
24h.
Chemical analysis Deltamethrin was extracted and
quantified using an AcclaimR C18 HPLC column.
Figure 4. Relationship between median time to
knockdown and deltamethrin on net.
Results
Figure 3. Median time to knockdown tests
HPLC analysis confirmed that the loading doses
were close to the target doses (Fig 1).
Deltamethrin was readily removed by washing from
the conventionally treated ITN after 5 washes
only 2.7 (0.8mg/m2) of the loading dose
remained. For KO-Tab 1-2-3, the loss of
deltamethrin was much slower insecticide content
was 73 of loading dose after 5 washes, 26 after
20 washes and 16 after 30 washes. For PermaNet,
the loss was slower still 41 after 20 washes
and 28 after 30 washes. For formulation BES903,
there was more variation, presumably due to
uneven distribution of insecticide after
hand-dipping.
Discussion The KO-Tab 1-2-3 formulation was a
major improvement over conventional deltamethrin
treatments. A significant deposit was present
even after 30 washes. Deltamethrin has high
affinity for polyester and a minute amount
remained bound to the conventional treated net to
give eventual knockdown even after 30 washes.
The next phase will be to test KO-Tab 1-2-3
treated nets against natural mosquito populations
in experimental huts. The ultimate test is
whether the treatment can withstand routine
wear-and-tear and washing over the lifetime of a
net in normal everyday use.
Conclusion KO-Tab 1-2-3 was confirmed to be a
long-lasting wash-resistant formulation. This
finding raises the hope that conventional nets
may require treatment only once through simple
home dipping. This single development, if widely
adopted, could greatly prolong the effectiveness
of conventionally treated nets and have a major
impact on malaria in Africa.
Figure 1. Concentration of deltamethin on netting
after washing