Multiple insecticide resistance in the major malaria vector Anopheles funestus in southern Ghana: implications for malaria control

Riveron et al. Parasites & Vectors (2016) 9:504 DOI 10.1186/s13071-016-1787-8 RESEARCH Open Access Multiple insecticide resistance in the major malaria vector Anopheles funestus in southern Ghana: implications for malaria control Jacob M. Riveron1,2* , Michael Osae3, Alexander Egyir-Yawson3, Helen Irving1, Sulaiman S. Ibrahim1,4 and Charles S. Wondji1,2 Abstract Background: Understanding the dynamics of insecticide resistance in African malaria vectors is crucial for successful implementation of resistance management strategies in the continent. This study reports a high and multiple insecticide resistance in Anopheles funestus from southern Ghana which could compromise the Malaria Operational Plan in this country, if not tackled. Adult Anopheles mosquitoes were collected in Obuasi and Adawukwa, in southern Ghana. Plasmodium infection rates, susceptibility to the main insecticides used in public health and the molecular basis of insecticide resistance were established. Results: An. funestus (sensu stricto) (s.s.) was the predominant mosquito species found resting inside the houses in Obuasi, while at Adawukwa it was found together with An. coluzzii. Parasite rates were high in An. funestus (s.s.) populations from both localities, with Plasmodium infection rates greater than 12.5 %. Both, An. funestus (s.s.) and An. coluzzii, from the two sites exhibited high resistance to the insecticide from various classes including the pyrethroids, carbamates and DDT, but remained fully susceptible to the organophosphates. A preliminary characterization of the underlying molecular mechanisms of resistance in An. funestus (s.s.) populations from both sites revealed that CYP6P9a, CYP6P9b, CYP6M7 and GSTe2 genes are upregulated, markedly higher in Obuasi (between 3.35 and 1.83 times) than in Adawukwa population. The frequency of L119F-GSTe2 and A296S-RDL resistance markers were also higher in Obuasi (42.5 and 68.95 % higher), compared with An. funestus (s.s.) populations from Adawukwa. These findings suggest that the similar resistance pattern observed in both An. funestus (s.s.) populations are driven by different mechanisms. Conclusions: Resistance to multiple insecticides in public health use is present in malaria vectors from Ghana with major resistance genes already operating in the field. This should be taken into consideration in the design of resistance management strategies to avoid operational failure. Keywords: Malaria, Insecticide resistance, Vector control, An. funestus, An. gambiae, An. coluzzii, Ghana * Correspondence: 1 Vector Biology Department, Liverpool School of Tropical Medicine, Pembroke Place, Liverpool, UK 2 Research Unit Liverpool School of Tropical Medicine, Organisation de Coordination pour la lutte contre les Endémies en Afrique Centrale, P.O Box 288, Yaoundé, Cameroon Full list of author information is available at the end of the article © 2016 The Author(s). Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Riveron et al. Parasites & Vectors (2016) 9:504 Background Malaria is endemic in Ghana with the entire population of 24.2 million at risk of infection and more than 3 million cases of clinical malaria reported annually, of which 900,000 cases are in children under the age of five [1]. To reduce this burden, the President’s Malaria Initiative (PMI), in collaboration with Ghana National Malaria Control Program and other partners, has developed the PMI/Ghana Malaria Operational Plan (MOP). Besides early diagnosis, intermittent preventive treatment of pregnant women and artemisinin-based combination therapies, MOP targets malaria vectors through free distribution of long-lasting insecticide-treated nets (LLINs) and a progressive scale up of indoor residual spraying (IRS) campaigns. Unfortunately, increasing insecticide resistance in malaria mosquitoes to the main insecticides used for both LLINs and IRS in Ghana and other African countries [2, 3] is threatening the continued effectiveness of these interventions. Insecticide resistance in malaria vectors is a dynamic process where the resistance pattern might change quickly because of selection pressures from both public health and agricultural practices [4, 5]. Implementation of successful resistance management strategies requires up-to-date information of insecticide resistant patterns in malaria vectors, as advised by the WHO Global Plan for Insecticide Resistance Management in Malaria Vectors [6], in order to utilise appropriate insecticides, and also to establish the molecular mechanisms driving the resistance. In Ghana, An. funestus (sensu stricto) (s.s.) along with An. gambiae (sensu lato) (s.l.), are the most important vectors of malaria, with An. funestus (s.s.) being prevalent in some areas of the country [7]. Several studies carried out between 2004 and 2010 throughout Ghana have shown that An. funestus (s.s.) populations are fully susceptible to deltamethrin (a type II pyrethroid), commonly used in LLINs and IRS, and to the organophosphate malathion. However, resistance to permethrin (a type I pyrethroid), also commonly used in LLINs and IRS, was detected in An. funestus (s.s.) for the first time in Obuasi, southern Ghana, in 2005 [8]. Resistance to other classes of insecticides used in public health such as the organochlorine dichlorodiphenyltrichloroethane (DDT) and the carbamate bendiocarb, was also reported in the same location in 2004 [2]. With no knockdown resistance (kdr) mutation detected so far in An. funestus, previous studies have demonstrated that pyrethroids and DDT resistance results from an increase in insecticide metabolism catalyzed mainly by the cytochrome P450s and glutathione S-transferases, with CYP6P9a, CYP6P9b, CYP6M7 and GSTe2 playing the key roles [9–11]. Beside the overexpression of these enzymes, it is acknowledged that the presence of L119FGSTe2 mutation confers DDT resistance in An. funestus (s.s.) populations in West/Central and East Africa, as the Page 2 of 9 119 F-GSTe2 enzyme is 3.4 times more efficient at metabolizing DDT in vitro than the L119-GSTe2 wild-type form [11]. However, the molecular mechanisms of insecticide resistance in Ghana remain uncharacterized. To assist the efforts of malaria vector control and help in developing effective resistance management plans, this study reports the contribution to malaria transmission and the insecticide resistant profile of two An. funestus (s.s.) populations collected in two dis (...truncated)