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Insecticide resistance in Culex quinquefasciatus from Zanzibar: implications for vector control programmes

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Jones, Christopher, Machin, Camille, Mohammed, Khalfan, Majambere, Silas, Ali, Abdullah S, Khatib, Bakari O, Mcha, Juma, Ranson, Hilary ORCID: https://orcid.org/0000-0003-2332-8247 and Kelly-Hope, Louise ORCID: https://orcid.org/0000-0002-3330-7629 (2012) 'Insecticide resistance in Culex quinquefasciatus from Zanzibar: implications for vector control programmes'. Parasites & Vectors, Vol 5, e78.

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Abstract

Background

Zanzibar has a long history of lymphatic filariasis (LF) caused by the filarial parasite Wuchereria
bancrofti, and transmitted by the mosquito Culex quinquefasciatus Say. The LF Programme in Zanzibar has
successfully implemented mass drug administration (MDA) to interrupt transmission, and is now in the elimination
phase. Monitoring infections in mosquitoes, and assessing the potential role of interventions such as vector control,
is important in case the disease re-emerges as a public health problem. Here, we examine Culex mosquito species
from the two main islands to detect W. bancrofti infection and to determine levels of susceptibility to the insecticides used for vector control.

Methods

Culex mosquitoes collected during routine catches in Vitongoji, Pemba Island, and Makadara, Unguja Island were tested for W. bancrofti infection using PCR. Insecticide bioassays on Culex mosquitoes were performed
to determine susceptibility to permethrin, deltamethrin, lambda-cyhalothrin, DDT and bendiocarb. Additional
synergism assays with piperonyl butoxide (PBO) were used for lambda-cyhalothrin. Pyrosequencing was used to determine the kdr genotype and sequencing of the mitochondrial cytochrome oxidase I (mtCOI) subunit
performed to identify ambiguous Culex species.

Results

None of the wild-caught Culex mosquitoes analysed were found to be positive for W. bancrofti. High frequencies of resistance to all insecticides were found in Wete, Pemba Island, whereas Culex from the nearby site of Tibirinzi (Pemba) and in Kilimani, Unguja Island remained relatively susceptible. Species identification confirmed
that mosquitoes from Wete were Culex quinquefasciatus. The majority of the Culex collected from Tibirinzi and all from Kilimani could not be identified to species by molecular assays. Two alternative kdr alleles, both resulting in a
L1014F substitution were detected in Cx. quinquefasciatus from Wete with no homozygote susceptible detected. Metabolic resistance to pyrethroids was also implicated by PBO synergism assays.

Conclusions

Results from the xenomonitoring are encouraging for the LF programme in Zanzibar. However, the
high levels of pyrethroid resistance found in the principle LF vector in Pemba Island will need to be taken into
consideration if vector control is to be implemented as part of the elimination programme.

Item Type: Article
Additional Information: The electronic version of this article is the complete one and can be found online at: http://www.parasitesandvectors.com/content/5/1/78
Subjects: QX Parasitology > Insects. Other Parasites > QX 530 Culex
QX Parasitology > Insects. Other Parasites > QX 600 Insect control. Tick control
WC Communicable Diseases > Tropical and Parasitic Diseases > WC 880 Filariasis and related conditions (General)
Faculty: Department: Groups (2002 - 2012) > Vector Group
Digital Object Identifer (DOI): https://doi.org/10.1186/1756-3305-5-78
Depositing User: Users 183 not found.
Date Deposited: 14 May 2012 08:23
Last Modified: 06 Sep 2019 10:55
URI: https://archive.lstmed.ac.uk/id/eprint/2835

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