When intensity of deltamethrin resistance in Anopheles gambiae s.l. leads to loss of Long Lasting Insecticidal Nets bio-efficacy : a case study in north Cameroon

Background: In Cameroon, insecticide resistance in Anopheles (An.) gambiae s.l. has been reported in several foci, prompting further investigations on associated patterns of Long-Lasting Insecticidal Nets (LLINs) bio-efficacy. The current study, conducted from June to August 2011, explored the intensity of deltamethrin resistance in An. gambiae s.l. from Pitoa and its impact on the residual bio-efficacy of LifeNet, a LLIN with deltamethrin incorporated into polypropylene nets (PND). Methods: Two-four days old females An. gambiae s.l. reared from larval collections in Pitoa were tested for susceptibility to DDT, permethrin and deltamethrin, using standard World Health Organization (WHO) tube assays. Intensity of deltamethrin resistance was explored using WHO tube assays, but across six working concentrations from 0.001 % to 0.5 %. Bio-efficacy of unwashed and washed PND was assessed using WHO cone test. Species identification and kdr 1014 genotyping were performed on mosquito samples that were not exposed to insecticides, using PCR-RFLP and HOLA methods respectively. The Kisumu reference susceptible strain of An. gambiae s.s. was used for comparisons. Results: A total of 1895 An. gambiae s.l. specimens from Pitoa were used for resistance and PND bio-efficacy testing. This mosquito population was resistant to DDT, permethrin and deltamethrin, with 18-40 min knockdown times for 50 % of tested mosquitoes and 59-77 % mortality. Deltamethrin Resistance Ratio compared with the Kisumu strain was estimated at >= 500 fold. LifeNets were effective against the susceptible Kisumu (100 % knockdown (KD60min) and mortality) and the resistant Pitoa samples (95 % KD60min, 83-95 % mortality). However, the bio-efficacy gradually dropped against the Pitoa samples when nets were washed (X-2 = 35.887, df = 8, p < 0.001), and fell under the WHO efficacy threshold (80 % mortality and/or 95 % KD60min) between 10 and 15 washes. The Pitoa samples were composed of three sibling species: An. arabiensis (132/154, 86 %), An. coluzzii (19/154, 12 %) and An. gambiae s.s. (3/154, 2 %). The kdr L1014F allele was found only in An. coluzzii (N-positive = 13/19), at 34 % frequency and heterozygote stage. No specimen carried the kdr L1014S allele. Conclusions: The current study showed that LifeNet might still offer some protection against the resistant An. gambiae s.l. population from Pitoa, provided appropriate dose of insecticide is available on the nets

Kdr-based insecticide resistance in Anopheles gambiae s.s populations in

<p>Abstract</p> <p>Background</p> <p>The spread of insecticide resistance in the malaria mosquito, <it>Anopheles gambiae </it>is a serious threat for current vector control strategies which rely on the use of insecticides. Two mutations at position 1014 of the S₆transmembrane segment of domain II in the voltage gated sodium channel, known as <it>kdr </it>(<it>knockdown resistance</it>) mutations leading to a change of a Leucine to a Phenylalanine (L1014F) or to a Serine (L1014S) confer resistance to DDT and pyrethroid insecticides in the insect. This paper presents the current distribution of the <it>kdr </it>alleles in wild <it>Anopheles gambiae </it>populations in Cameroon.</p> <p>Results</p> <p>A total of 1,405 anopheline mosquitoes were collected from 21 localities throughout Cameroon and identified as <it>An. gambiae </it>(N = 1,248; 88.8%), <it>An. arabiensis </it>(N = 120; 8.5%) and <it>An. melas </it>(N = 37; 2.6%). Both <it>kdr </it>alleles 1014F and 1014S were identified in the M and S molecular forms of <it>An. gambiae </it>s.s. The frequency of the 1014F allele ranged from 1.7 to 18% in the M-form, and from 2 to 90% in the S-form. The 1014S allele ranged from 3-15% in the S-form and in the M-form its value was below 3%. Some specimens were found to carry both resistant <it>kdr </it>alleles.</p> <p>Conclusion</p> <p>This study provides an updated distribution map of the <it>kdr </it>alleles in wild <it>An. gambiae </it>populations in Cameroon. The co-occurrence of both alleles in malaria mosquito vectors in diverse ecological zones of the country may be critical for the planning and implementation of malaria vector control interventions based on IRS and ITNs, as currently ongoing in Cameroon.</p

Field efficacy of a new mosaic long-lasting mosquito net (PermaNet® 3.0) against pyrethroid-resistant malaria vectors: a multi centre study in Western and Central Africa

<p>Abstract</p> <p>Background</p> <p>Due to the spread of pyrethroid-resistance in malaria vectors in Africa, new strategies and tools are urgently needed to better control malaria transmission. The aim of this study was to evaluate the performances of a new mosaic long-lasting insecticidal net (LLIN), i.e. PermaNet^®3.0, against wild pyrethroid-resistant <it>Anopheles gambiae s.l</it>. in West and Central Africa.</p> <p>Methods</p> <p>A multi centre experimental hut trial was conducted in Malanville (Benin), Vallée du Kou (Burkina Faso) and Pitoa (Cameroon) to investigate the exophily, blood feeding inhibition and mortality induced by PermaNet^®3.0 (i.e. a mosaic net containing piperonyl butoxide and deltamethrin on the roof) comparatively to the WHO recommended PermaNet^®2.0 (unwashed and washed 20-times) and a conventionally deltamethrin-treated net (CTN).</p> <p>Results</p> <p>The personal protection and insecticidal activity of PermaNet 3.0 and PermaNet^®2.0 were excellent (>80%) in the "pyrethroid-tolerant" area of Malanville. In the pyrethroid-resistance areas of Pitoa (metabolic resistance) and Vallée du Kou (presence of the L1014F <it>kdr </it>mutation), PermaNet^®3.0 showed equal or better performances than PermaNet^®2.0. It should be noted however that the deltamethrin content on PermaNet^®3.0 was up to twice higher than that of PermaNet^®2.0. Significant reduction of efficacy of both LLIN was noted after 20 washes although PermaNet^®3.0 still fulfilled the WHO requirement for LLIN.</p> <p>Conclusion</p> <p>The use of combination nets for malaria control offers promising prospects. However, further investigations are needed to demonstrate the benefits of using PermaNet^®3.0 for the control of pyrethroid resistant mosquito populations in Africa.</p

Distribution of knock-down resistance mutations in Anopheles gambiae molecular forms in west and west-central Africa

<p>Abstract</p> <p>Background</p> <p><it>Knock-down </it>resistance (<it>kdr</it>) to DDT and pyrethroids in the major Afrotropical vector species, <it>Anopheles gambiae </it>sensu stricto, is associated with two alternative point mutations at amino acid position 1014 of the voltage-gated sodium channel gene, resulting in either a leucine-phenylalanine (L1014F), or a leucine-serine (L1014S) substitution. In <it>An. gambiae </it>S-form populations, the former mutation appears to be widespread in west Africa and has been recently reported from Uganda, while the latter, originally recorded in Kenya, has been recently found in Gabon, Cameroon and Equatorial Guinea. In M-form populations surveyed to date, only the L1014F mutation has been found, although less widespread and at lower frequencies than in sympatric S-form populations.</p> <p>Methods</p> <p><it>Anopheles gambiae </it>M- and S-form specimens from 19 sites from 11 west and west-central African countries were identified to molecular form and genotyped at the <it>kdr </it>locus either by Hot Oligonucleotide Ligation Assay (HOLA) or allele-specific PCR (AS-PCR).</p> <p>Results</p> <p>The <it>kdr </it>genotype was determined for about 1,000 <it>An. gambiae </it>specimens. The L1014F allele was found at frequencies ranging from 6% to 100% in all S-form samples (N = 628), with the exception of two samples from Angola, where it was absent, and coexisted with the L1014S allele in samples from Cameroon, Gabon and north-western Angola. The L1014F allele was present in M-form samples (N = 354) from Benin, Nigeria, and Cameroon, where both M- and S-forms were sympatric.</p> <p>Conclusion</p> <p>The results represent the most comprehensive effort to analyse the overall distribution of the L1014F and L1014S mutations in <it>An. gambiae </it>molecular forms, and will serve as baseline data for resistance monitoring. The overall picture shows that the emergence and spread of <it>kdr </it>alleles in <it>An. gambiae </it>is a dynamic process and that there is marked intra- and inter-form heterogeneity in resistance allele frequencies. Further studies are needed to determine: i) the importance of selection pressure exerted by both agricultural and public health use of pyrethroid insecticides, ii) the phenotypic effects, particularly when the two mutations co-occur; and iii) the epidemiological importance of <it>kdr </it>for both pyrethroid- and DDT-based malaria control operations, particularly if/when the two insecticides are to be used in concert.</p

Efficacy of bifenthrin-impregnated bednets against Anopheles funestus and pyrethroid-resistant Anopheles gambiae in North Cameroon

BACKGROUND: Recent field studies indicated that insecticide-treated bednets (ITNs) maintain their efficacy despite a high frequency of the knock-down resistance (kdr) gene in Anopheles gambiae populations. It was essential to evaluate ITNs efficacy in areas with metabolic-based resistance. METHODS: Bifenthrin was used in this experiment because it is considered a promising candidate for bednets impregnation. Nets were treated at 50 mg/m(2), a dose that has high insecticidal activity on kdr mosquitoes and at 5 mg/m(2), a dose that kills 95% of susceptible mosquitoes under laboratory conditions with 3 minutes exposure. Bednets were holed to mimic physical damage. The trial was conducted in three experimental huts from Pitoa, North-Cameroon where Anopheles gambiae displays metabolic resistance and cohabits with An. funestus. RESULTS: Bifenthrin at 50 mg/m(2 )significantly reduced anophelines' entry rate (>80%). This was not observed at 5 mg/m(2). Both treatments increased exophily in An. gambiae, and to a lesser extent in An. funestus. With bifenthrin at high dosage, over 60% reduction in blood feeding and 75–90% mortality rates were observed in both vectors. Despite presence of holes, only a single An. gambiae and two An. funestus females were collected inside the treated net, and all were found dead. The same trends were observed with low dosage bifenthrin though in most cases, no significant difference was found with the untreated control net. CONCLUSION: Bifenthrin-impregnated bednets at 50 mg/m(2 )were efficient in the reduction of human-vector contact in Pitoa. Considerable personal protection was gained against An. funestus and metabolic pyrethroid resistant An. gambiae populations

Analysis of Expression Pattern and Genetic Deletion of Netrin5 in the Developing Mouse

Boundary cap cells are a transient, neural-crest-derived population found at the motor exit point and dorsal root entry zone of the embryonic spinal cord. These cells contribute to the central/peripheral nervous system boundary, and in their absence neurons and glia from the CNS migrate into the PNS. We found Netrin5 (Ntn5), a previously unstudied member of the netrin gene family, to be robustly expressed in boundary cap cells. We generated Ntn5 knockout mice and examined neurodevelopmental and boundary-cap-cell-related phenotypes. No abnormalities in cranial nerve guidance, dorsal root organization, or sensory projections were found. However, Ntn5 mutant embryos did have ectopic motor neurons that migrated out of the ventral horn and into the motor roots. Previous studies have implicated semaphorin6A (Sema6A) in boundary cap cells signaling to plexinA2 (PlxnA2)/neuropilin2 (Nrp2) in motor neurons in restricting motor neuron cell bodies to the ventral horn, particularly in the caudal spinal cord. In Ntn5 mutants, ectopic motor neurons are likely to be a different population, as more ectopias were found rostrally. Furthermore, ectopic motor neurons in Ntn5 mutants were not immunoreactive for NRP2. The netrin receptor DCC is a potential receptor for NTN5 in motor neurons, as similar ectopic neurons were found in Dcc mutant mice, but not in mice deficient for other netrin receptors. Thus, Ntn5 is a novel netrin family member that is expressed in boundary cap cells, functioning to prevent motor neuron migration out of the CNS

Trends in DDT and pyrethroid resistance in Anopheles gambiae s.s. populations from urban and agro-industrial settings in southern Cameroon

Background: Pyrethroid insecticides are widely used for insect pest control in Cameroon. In certain insect species, particularly the malaria vector Anopheles gambiae, resistance to this class of insecticides is a source of great concern and needs to be monitored in order to sustain the efficacy of vector control operations in the fields. This study highlights trends in DDT and pyrethroid resistance in wild An. gambiae populations from South Cameroon. Methods: Mosquitoes were collected between 2001 and 2007 in four sites in South Cameroon, where insecticides are used for agricultural or personal protection purposes. Insecticide use was documented in each site by interviewing residents. Batches of 2-4 days old adult female mosquitoes reared from larval collections were tested for susceptibility to DDT, permethrin and deltamethrin using standard WHO procedures. Control, dead and survivors mosquitoes from bioassays were identified by PCR-RFLP and characterized for the kdr mutations using either the AS-PCR or the HOLA method. Results: Four chemical insecticide groups were cited in the study sites: organochlorines, organophosphates, carbamates and pyrethroids. These chemicals were used for personal, crop or wood protection. In the four An. gambiae populations tested, significant variation in resistance levels, molecular forms composition and kdr frequencies were recorded in the time span of the study. Increases in DDT and pyrethroid resistance, as observed in most areas, were generally associated with an increase in the relative frequency of the S molecular form carrying the kdr mutations at higher frequencies. In Mangoum, however, where only the S form was present, a significant increase in the frequency of kdr alleles between 2003 to 2007 diverged with a decrease of the level of resistance to DDT and pyrethroids. Analyses of the kdr frequencies in dead and surviving mosquitoes showed partial correlation between the kdr genotypes and resistance phenotypes, suggesting that the kdr mechanism may act with certain cofactors to be identified. Conclusion: These results demonstrate the ongoing spread of kdr alleles in An. gambiae in Central Africa. The rapid evolution of insecticide resistance in this highly dynamic and genetically polymorphic species remains a challenge for its control

Insecticide resistance in Anopheles gambiae from south-western Chad, Central Africa

<p>Abstract</p> <p>Background</p> <p>Indoor residual spraying and insecticide-treated nets (ITN) are essential components of malaria vector control in Africa. Pyrethroids are the only recommended compounds for nets treatment because they are fast-acting insecticides with low mammalian toxicity. However, there is growing concern that pyrethroid resistance may threaten the sustainability of ITN scaling-up programmes. Here, insecticide susceptibility was investigated in <it>Anopheles gambiae </it>sensu lato from an area of large scale ITN distribution programme in south-western Chad.</p> <p>Methods</p> <p>Susceptibility to 4% DDT, 0.05% deltamethrin, 0.75% permethrin, 0.1% bendiocarb and 5% malathion was assessed using the WHO standard procedures for adult mosquitoes. Tests were carried out with two to four days-old, non-engorged female mosquitoes. The <it>An. gambiae </it>Kisumu strain was used as a reference. Knockdown effect was recorded every 5 min and mortality scored 24 h after exposure. Mosquitoes were identified to species and molecular form by PCR-RFLP and genotypes at the <it>kdr </it>locus were determined in surviving specimens by Hot Oligonucleotide Ligation Assay (HOLA).</p> <p>Results</p> <p>During this survey, full susceptibility to malathion was recorded in all samples. Reduced susceptibility to bendiocarb (mortality rate of 96.1%) was found in one sample out of nine assayed. Increased tolerance to pyrethroids was detected in most samples (8/9) with mortality rates ranging from 70.2 to 96.6% for deltamethrin and from 26.7 to 96.3% for permethrin. Pyrethroid tolerance was not associated with a significant increase of knock-down times. <it>Anopheles arabiensis </it>was the predominant species of the <it>An. gambiae </it>complex in the study area, representing 75 to 100% of the samples. Screening for <it>kdr </it>mutations detected the L1014F mutation in 88.6% (N = 35) of surviving <it>An</it>. <it>gambiae </it>sensu stricto S form mosquitoes. All surviving <it>An. arabiensis </it>(N = 49) and M form <it>An</it>. <it>gambiae </it>s.s. (N = 1) carried the susceptible allele.</p> <p>Conclusion</p> <p>This first investigation of malaria vector susceptibility to insecticides in Chad revealed variable levels of resistance to pyrethroid insecticides (permethrin and deltamethrin) in most <it>An</it>. <it>gambiae </it>s.l. populations. Resistance was associated with the L1014F <it>kdr </it>mutation in the S form of <it>An. gambiae </it>s.s.. Alternative mechanisms, probably of metabolic origin are involved in <it>An. arabiensis</it>. These results emphasize the crucial need for insecticide resistance monitoring and in-depth investigation of resistance mechanisms in malaria vectors in Chad. The impact of reduced susceptibility to pyrethroids on ITN efficacy should be further assessed.</p

Design of a Two-level Adaptive Multi-Agent System for Malaria Vectors driven by an ontology

<p>Abstract</p> <p>Background</p> <p>The understanding of heterogeneities in disease transmission dynamics as far as malaria vectors are concerned is a big challenge. Many studies while tackling this problem don't find exact models to explain the malaria vectors propagation.</p> <p>Methods</p> <p>To solve the problem we define an Adaptive Multi-Agent System (AMAS) which has the property to be elastic and is a two-level system as well. This AMAS is a dynamic system where the two levels are linked by an Ontology which allows it to function as a reduced system and as an extended system. In a primary level, the AMAS comprises organization agents and in a secondary level, it is constituted of analysis agents. Its entry point, a User Interface Agent, can reproduce itself because it is given a minimum of background knowledge and it learns appropriate "behavior" from the user in the presence of ambiguous queries and from other agents of the AMAS in other situations.</p> <p>Results</p> <p>Some of the outputs of our system present a series of tables, diagrams showing some factors like Entomological parameters of malaria transmission, Percentages of malaria transmission per malaria vectors, Entomological inoculation rate. Many others parameters can be produced by the system depending on the inputted data.</p> <p>Conclusion</p> <p>Our approach is an intelligent one which differs from statistical approaches that are sometimes used in the field. This intelligent approach aligns itself with the distributed artificial intelligence. In terms of fight against malaria disease our system offers opportunities of reducing efforts of human resources who are not obliged to cover the entire territory while conducting surveys. Secondly the AMAS can determine the presence or the absence of malaria vectors even when specific data have not been collected in the geographical area. In the difference of a statistical technique, in our case the projection of the results in the field can sometimes appeared to be more general.</p