KNOCKDOWN RESISTANCETYPE PYRETHROID RESISTANCE IN

1
KNOCKDOWN RESISTANCE-TYPE PYRETHROID RESISTANCE
IN ANOPHELES GAMBIAE SENSU STRICTO FROM
SOUTH-EASTERN GHANA K Adasi J Hemingway SCHOOL
OF TROPICAL MEDICINE PEMBROKE PLACE LIVERPOOL
L3 5QA UNITED KINGDOM
LIVERPOOL SCHOOL OF TROPICAL MEDICINE
Background and methods Pyrethroid resistance due
to kdr in Anopheles gambiae s.s., the most
efficient malaria vector in sub-Saharan Africa,
seems to be widespread in West Africa. However,
in Ghana the insecticide resistance status of
this vector had not been investigated. Anopheline
larvae were collected from south-eastern Ghana in
2002, reared to adults and morphologically
identified as An. gambiae sensu lato and further
identified by PCR-RFLP as An. gambiae s.s. and
molecular M and S forms. Almost 1,400 three-day
old female mosquitoes were selected for
susceptibility tests with 0.75 permethrin, 0.05
deltamethrin and 0.05 lambda-cyhalothrin. The
extent of pyrethroid resistance in the
field-collected mosquitoes was determined by
comparison with similar tests using 476 female
mosquitoes of laboratory strain An. gambiae
Kisumu, known to be susceptible to pyrethroids.
The kdr allele that confers resistance to
pyrethroids and DDT was detected by diagnostic PCR
Results
Species identification All 527 mosquito samples
identified by PCR-RFLP were An. gambiae s.s.,
with 95.3 (502) S-forms, 3.8 (20) M-forms and
0.9 M-S hybrids
Pyrethroid susceptibility tests
Example of probit analysis of susceptibility
tests data Comparison of efficacy of permethrin
in resistant (field) and susceptible (laboratory)
An. gambiae
Figure 1 0.75 Permethrin bioassay-Field-collecte
d mosquito samples
Figure 2 0.75 Permethrin bioassay-susceptible
Kisumu strain of An. gambiae s.s
Resistance ratios - Permethrin 5.8-8.5
L-cyhalothrin 3.0-3.5 Deltamethrin 2.0-2.4
Diagnostic PCR for detecting knockdown resistance
(kdr) mutation
Table 1 Kdr detection by PCR
Kdr status
Figure 3 Sodium channel. Kdr mutation in
transmembrane VI of Domain II (Denac et al.,
2000).
Conclusions

• The predominant malaria vector in south-eastern
  Ghana is An. gambiae s.s and does not occur in
  sympatry with other members of the species
  complex
• The kdr gene occurs with very high frequency (
  0.90) and is found mainly in the S-form of An.
  gambiae s.s
• Kdr may not necessarily reduce the efficacy of
  pyrethroid-impregnated bednets

Acknowledgment My research is funded by Gates
Malaria Partnership Doctoral Scholarship