The emergence of pyrethroid resistant Anopheles funestus (a major African vector) in
malaria affected parts of KwaZuluNatal,
South Africa was correlated with the
malaria epidemic of 1996 2000.
This finding prompted the necessity of
incorporating insecticide resistance management strategies into formal malaria
control policy in South Africa. Resistance management strategies often rely on the
assumption of reduced fitness associated with insecticide resistance and are based on
the principle that resistance genes will tend to drift out of vector populations in the
absence of insecticide selection pressure. This study aimed to determine whether a
fitness cost is associated with pyrethroid resistance as well as to determine the
stability and mode of inheritance of the resistance genes in a pyrethroid resistant
(FUMOZR)
strain of An. funestus. It also aimed to sequence and analyze a segment
of the sodium channel gene for any kdrtype
mutation(s) that may be associated with
pyrethroid resistance. The final aim was to determine the resistance mechanisms
involved in a Ghanaian field population of An. funestus resistant to DDT and
pyrethroids.
Results obtained suggest that pyrethroid resistance in southern African An. funestus
did not incur any loss of fitness. FUMOZR
had a reproductive advantage over a
pyrethroid susceptible An. funestus strain (FANG) in terms of higher fertility,
proportion of females laying eggs and eggtoadult
survivorship, and a lower sterility
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iv
rate. However, FUMOZR
had a slower developmental time from egg hatch to adult
emergence than FANG.
Results of crosses and backcrosses carried out between FUMOZR
and FANG were
consistent with a monofactorial and autosomal mode of inheritance in which the
resistant genes presented as incompletely dominant. The resistant gene was found to
be stable over several generations in the absence of insecticide selection pressure.
Analysis of the genomic and mRNA sequences of the IIS5 IIS6
segment of the
sodium channel gene showed a high sequence identity between FUMOZR
and
FANG suggesting that the two strains are genetically similar. The kdrtype
mutation
was absent from this region supporting previous evidence that the resistance
mechanism is primarily metabolic.
Bioassay data showed that a Ghanaian field population of An. funestus from Obuasi,
Ghana, was resistant to DDT and pyrethroids. Molecular analysis of the IIS5 IIS6
segment of the sodium channel gene showed an absence of kdrtype
mutations
previously associated with insecticide resistance. Biochemical analysis suggests that
resistance is metabolically mediated primarily by elevated levels of and esterases
with monooxygenases and GSTs playing a lesser role. The presence of an altered
acetylcholinesterase conferring carbamate resistance was also evident in the
population. These results have implications for the management of resistance in
malaria control programmes in Africa.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/5761 |
| Date | 15 October 2008 |
| Creators | Okoye, Patricia Nkem |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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