Biochemical basis of permethrin resistance in Anopheles arabiensis from Lower Moshi, north-eastern Tanzania.
BACKGROUND
Development of resistance to different classes of insecticides is a potential threat to malaria control. With the increasing coverage of long-lasting insecticide-treated nets in Tanzania, the continued monitoring of resistance in vector populations is crucial. It may facilitate the development of novel strategies to prevent or minimize the spread of resistance. In this study, metabolic-based mechanisms conferring permethrin (pyrethroid) resistance were investigated in Anopheles arabiensis of Lower Moshi, Kilimanjaro region of north-eastern Tanzania.


METHODS
WHO susceptibility test kits were used to detect resistance to permethrin in An. arabiensis. The levels and mechanisms of permethrin resistance were determined using CDC bottle bioassays and microplate (biochemical) assays. In bottle bioassays, piperonyl butoxide (PBO) and s,s,s-tributyl phosphorotrithioate (DEF) were used as synergists to inhibit mixed function oxidases and non-specific esterases respectively. Biochemical assays were carried out in individual mosquitoes to detect any increase in the activity of enzymes typically involved in insecticide metabolism (mixed function oxidases, alpha- and beta-esterases).


RESULTS
Anopheles arabiensis from the study area was found to be partially resistant to permethrin, giving only 87% mortality in WHO test kits. Resistance ratios at KT50 and KT95 were 4.0 and 4.3 respectively. The permethrin resistance was partially synergized by DEF and by PBO when these were mixed with permethrin in bottle bioassays and was fully synergized when DEF and PBO were used together. The levels of oxidase and beta-esterase activity were significantly higher in An. arabiensis from Lower Moshi than in the laboratory susceptible strain. There was no difference in alpha-esterase activity between the two strains.


CONCLUSIONS
Elevated levels of mixed function oxidases and beta-esterases play a role in detoxification of permethrin in the resistant An. arabiensis population of Lower Moshi.
Matowo
Johnson
J
Pan-African Malaria Vector Research Consortium www.pamverc.org. johntowo@yahoo.com
Kulkarni
Manisha A
MA
Mosha
Franklin W
FW
Oxborough
Richard M
RM
Kitau
Jovin A
JA
Tenu
Filemoni
F
Rowland
Mark
M
D000818:Animals; D000852:Anopheles / Q000187:drug effects* / Q000201:enzymology*; D001681:Biological Assay; D004791:Enzyme Inhibitors / Q000378:metabolism / Q000494:pharmacology*; D004950:Esterases / Q000378:metabolism*; D007305:Insecticide Resistance; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D009032:Mosquito Control / Q000379:methods; D063086:Organothiophosphates; D026023:Permethrin / Q000378:metabolism / Q000494:pharmacology*; D010574:Pesticide Synergists / Q000378:metabolism / Q000494:pharmacology; D010882:Piperonyl Butoxide; D013636:Tanzania
D004791:Enzyme Inhibitors; D063086:Organothiophosphates; D010574:Pesticide Synergists; D026023:Permethrin; C006863:butyl phosphorotrithioate; D006899:Mixed Function Oxygenases; D004950:Esterases; D010882:Piperonyl Butoxide