Insecticide resistance and vector status of Anopheles funestus and An. gambiae populations at a sugar estate in Mozambique
Date
2010-04-12T09:55:50Z
Authors
Kloke, Ronald Graham
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Abstract
Malaria is on the increase in Mozambique since 2001 and impacts primarily on
children < 5 years of age. Insecticide resistance in the malaria vector mosquitoes is on
the increase in Mozambique and Africa and is cause for serious concern. Maragra
sugar estate is situated in close proximity to the nKomati river floodplain in a rural
area in Mozambique and requires intense irrigation for cane growing and as a result
provides extensive breeding sites for An. funestus and other mosquitoes. In the areas
surrounding the estate there are two important vectors of malaria, Anopheles funestus
group and An. gambiae complex. There is intense malaria transmission in the areas
surrounding the sugar estate and the last entomological study on the vectors in the
Manhica area was done in 1998. It was becoming increasingly urgent to identify to
species level the vectors in this area and to monitor the insecticide resistance status of
these vectors. Due to leakage (theft) of insecticides and a change by the National
Malaria Control Programme (NMCP) to an insecticide to which the predominant
vector is resistant, an entomological survey was carried out in this area from January
2009 to March 2009 to ascertain by Polymerase chain reaction (PCR) what species of
malaria vectors were present inside and outside of the Maragra vector control area,
their population levels and their vectorial status in these two areas. Insecticide
resistance studies by insecticide exposure and the synergist piperonyl butoxide (pbo)
were carried out using the World Health Organisation (WHO) bioassay method on
collected An. funestus mosquitoes. This was done to establish this species resistance
status to the four classes of insecticides recommended by the WHO for malaria vector
control. The collections of An. arabiensis and An. merus that were identified were too
few to carry out insecticide resistance tests on these two species. Enzyme linked
v
immuno-sorbent assay (ELISA) tests were undertaken to establish the vectorial
capacity of Anopheles funestus and An. gambiae complex in this area. The
predominant malaria vector species in this area is An. funestus s.s., with the secondary
vector being An. arabiensis. An. funestus has a high vectorial capacity in this area and
found to have a Plasmodium falciparum sporozoite rate of 6.02%. This is an increase
in the sporozoite rate of 1.2% from 1998 when the last survey in this regard was
carried out. Coupled with this increase is an increase in the An. funestus populations
in this area since this time. One An. gambiae complex sample was found to be
positive but the species is not known as this particular sample did not amplify on
PCR. Anopheles funestus is highly resistant to synthetic pyrethroids and exhibits a
lower level of resistance to bendiocarb, a carbamate insecticide in use at Maragra
sugar estate. The synergist pbo mediates the resistance mechanism in both these
insecticides indicating that the metabolic resistance mechanism present in this
mosquito is strongly mediated by monooxygenase detoxification. The role of the
medical entomologist is increasingly necessary and important in the monitoring of this
resistance phenomenon in malaria vector mosquitoes, as is the role of the vector
control programme manager in implementing and managing vector control
programmes. The implication of cane sugar farming and its impact on vector
production and malaria transmission is discussed. Insecticide resistance and the
change by the NMCP to a synthetic pyrethroid to which the predominant vector of
malaria is resistant is discussed.
Description
MSc (Med), Faculty of Health Sciences, University of the Witwatersrand, 2009
Keywords
insecticide, malaria, Mozambique, Anopheles funestus, Anopheles gambiae