Reduced bio-efficacy of permethrin EC impregnated bednets against an Anopheles gambiae strain with oxidase-based pyrethroid tolerance

BACKGROUND: Insecticide-treated nets (ITNs) are an integral component of malaria control programmes in Africa. How much pyrethroid resistance in malaria vectors will impact on the efficacy of ITNs is controversial. The purpose of this study was to evaluate knockdown and killing effects of ITNs on a metabolic-based resistant or tolerant malaria vector strain. METHODS: Bio-efficacy of 500 mg/m(2 )permethrin EC treated bednets was assessed on the OCEAC laboratory (OC-Lab) strain of Anopheles gambiae s.s.. This strain is resistant to DDT and tolerant to pyrethroids, with elevated mixed function oxidases. The Kisumu reference susceptible strain of A. gambiae s.s. was used as control. Nets were impregnated in February 1998 and used by households of the Ebogo village. Then they were collected monthly over six months for Bio-assays (WHO cone test). Knockdown and mortality rates were compared between the OC-Lab and the Kisumu strains, by means of the Mantel-Haenszel chi-square test. RESULTS: During the whole trial, permethrin EC knockdown rates were impressive (mostly higher than 97%). No significant difference was observed between the two strains. However, the mortality rates were significantly decreased in the OC-Lab strain (40–80%) compared with that of the Kisumu strain (75–100%). The decrease of killing effect on the OC-Lab strain was attributed to permethrin EC tolerance, due to the high oxidase metabolic activity. CONCLUSION: These data suggested an impact of pyrethroid tolerance on the residual activity of ITNs. More attention should be given to early detection of resistance using biochemical or molecular assays for better resistance management

Syntheses And Characterization Of Bis(amino)cyclodiphosphazane Complexes Of Group 4- And -15 Elements

In the first part of this work, the interaction of sodium tert-butoxide and sulfur with Group 4 metal bis(tert-butylamido)cyclodiphosph(III)azanes dichlorides, {[tBuNP)2tBuN)2]MCl2}, where M is Zr or Hf, is reported. The reaction of two equivalents of NaOtBu with {[tBuNP)2tBuN)2]MCl2}, M = Zr, Hf, resulted in the isolation of the first metal alkoxide complexes {[tBuNP)2tBuN)2]M(OtBu)2}, 35 (M =Zr) and 36 (M = Hf) of cyclodiphosphazanes. The oxidation of compounds 35 and 36 with elemental sulfur yielded {[tBuNP=S)2tBuN)2]M(OtBu)2}, 37 (M = Zr) and 38 (M = Hf), respectively. Similarly, the oxidation of {[tBuNP)2tBuN)2]MCl2}, M = Zr, Hf, with elemental sulfur led to the isolation of {[tBuNP=S)2tBuN)2]MCl2}, 39 (M = Zr) and 40 (M = Hf). The structures of compounds 37–40 were determined by X-ray crystallography and confirmed by multi-nuclear NMR spectroscopy and elemental analysis. In part two, the attack of two equivalents of the electrophiles Ph2PCl, PCl3, and CH3I on the dianionic bis(alkylamido)cyclodiphosph(III)azanes, {R = tert-butyl (48), cyclohexyl (54)} is described. The reaction of [(tBuNP)2(tBuNLi·thf)2 with Ph2PCl led to the isolation of two products: an asymmetric P, N product, 52A and a symmetric P, P substituted heterocycle, 52B. Treatment of cis-[(tBuNE)2(RNLi·thf)2], E = P, SiCH3 and R = tBu, Cy, with PCl3 yielded cis-{[E(μ-NtBu)]2(RNPCl2)2}, 55 (E = P, R = Cy) and 57 (E = SiCH3, R = tBu). While the reaction of MeI with compound 48 resulted in the isolation of the symmetrical product cis-{[(tBuNPMe)2(tBuNLi·thf)2]I2}, 58. Also, the lithiation of compound 59 with n-BuLi yielded 60. Compounds 52A, 52B, 54, 55, 57, and 60 were characterized by multi-nuclear NMR spectroscopy, X-ray crystallography, and elemental analysis. The last part of this work describes the syntheses and characterization of compounds derived from the reactions of {[(tBuNP)2(tBuN)2]ECl}, E = P, Sb, with various reagents. Treatment of {[(tBuNP)2(tBuN)2]PCl} with excess sulfur, AgSO3CF3, PhMgCl, and NaOtBu led to the isolation of the compounds [(tBuNP=S)3N], 66, [(tBuNP)2(tBuN)2]P]+SO3CF3-, 67, {[(tBuNP)2(tBuN)2]PPh}, 68, and {[(tBuNP)2(tBuN)2]POtBu}, 70, respectively. Meanwhile, oxidation of compound 68 with elemental sulfur resulted in {[(tBuNP)2(tBuN)2](P=S)Ph}, 69. Also, the reaction of {[(tBuNP)2(tBuN)2]SbCl} with PhMgCl and NaOtBu yiedeld {[(tBuNP)2(tBuN)2]SbPh}, 71 and {[(tBuNP)2(tBuN)2]SbOtBu}, 72, respectively. The structures of compounds 66, 67, 69, and 71 were determined by X-ray crystallography and confirmed by multi-nuclear NMR spectroscopy and elemental analysis

TEACHERS’ CHARACTERISTICS AND ITS IMPACT ON STUDENTS' PROFESSIONAL TRAINING IN THE TEACHERS' TRAINING COLLEGES IN FAKO DIVISION, CAMEROON

The purpose of this study was to examine teachers’ characteristics and their impact on students’ professional training in some teacher training schools in Fako Division, the south west region of Cameroon. This study employed a descriptive survey research design with a target population of 100 teachers in two teachers’ training colleges as respondents. Three research objectives were formulated for that purpose which was later transformed into research questions. Data was gathered through the use of questionnaires and was analyzed using Statistical Package for the Social Sciences. The findings reveal there was a positive relationship between teachers’ content mastery, communication, motivation, and personality on student’s professional training. Thus, based on the findings the following recommendations were made; teachers should communicate instructions in simple and clear language so that students will be able to understand also government should constantly organize seminars that will enable teachers to upgrade their knowledge, learn new skills, and become productive.  Article visualizations

Combating Forced Labour and Human Trafficking in Africa: The Role of Endogenous and Exogenous Forces

It is widely believed that indigenous culture and tradition are at the root of the human trafficking and forced labour problem in Africa. Adherents to this viewpoint also claim that endogenous as opposed to exogenous forces impede efforts to eradicate the problem. This study employed a loglinear regression model to test the tenability of this claim. It hypothesized an inverse association between indigenous culture/tradition and efforts to combat human trafficking. The hypothesis was rejected. It is shown that anti-trafficking initiatives are less successful where indigenous tradition is dominated, or has been usurped, by imported cultural practices. Key words: Africa’s triple heritage, Child labour, forced labour, human trafficking

A significant increase in kdr in Anopheles gambiae is associated with an intensive vector control intervention in Burundi highlands.

OBJECTIVES AND METHODS: In Burundi, the occurrence of the knock down resistance (kdr) mutation in Anopheles gambiae sensu lato (s.l.) was determined for six consecutive years within the framework of a vector control programme. Findings were also linked with the insecticide resistance status observed with bioassay in An. gambiae s.l. and An. funestus. RESULTS: The proportion of An. gambiae s.l. carrying the East Leu-Ser kdr mutation was 1% before the spraying intervention in 2002; by 2007 it was 86% in sprayed valleys and 67% in untreated valleys. Multivariate analysis showed that increased risk of carrying the kdr mutation is associated with spraying interventions, location and time. In bioassays conducted between 2005 and 2007 at five sites, An. funestus was susceptible to permethrin, deltamethrin and DDT. Anopheles gambiae s.l. remained susceptible or tolerant to deltamethrin and resistant to DDT and permethrin, but only when kdr allele carriers reached 90% of the population. CONCLUSIONS: The cross-resistance against DDT and permethrin in Karuzi suggests a possible kdr resistance mechanism. Nevertheless, the homozygous resistant genotype alone does not entirely explain the bioassay results, and other mechanisms conferring resistance cannot be ruled out. After exposure to all three insecticides, homozygote individuals for the kdr allele dominate among the surviving An. gambiae s.l. This confirms the potential selection pressure of pyrethroids on kdr mutation. However, the high occurrence of the kdr mutation, even at sites far from the sprayed areas, suggests a selection pressure other than that exerted by the vector control programme

Insecticide susceptibility of Aedes aegypti and Aedes albopictus in Central Africa

<p>Abstract</p> <p>Background</p> <p><it>Aedes aegypti </it>(Linnaeus, 1762) and <it>Aedes albopictus </it>(Skuse, 1894) are the main vectors of dengue (DENV) and chikungunya (CHIKV) viruses worldwide. As there is still no vaccine or specific treatment for DENV and CHIKV, vector control remains the cornerstone of prevention and outbreak control. Unfortunately, vector control programs are facing operational challenges with mosquitoes becoming resistant to commonly used insecticides in several areas through the world. Throughout Central Africa no recent data are available susceptible/resistant status of either vector species since the introduction/arrival of <it>Ae. albopictus </it>in this area. We therefore studied the level of resistance of these two major vectors to insecticides commonly used in Africa for mosquito control.</p> <p>Results</p> <p><it>Aedes aegypti </it>and <it>Ae. albopictus </it>were sampled in six urban localities of Cameroon (Garoua, Bertoua, Yaoundé, Bafia, Buea) and Gabon (Libreville). Larval bioassays, carried out to determine the lethal concentrations (LC₅₀and LC₉₅) and resistance ratios (RR₅₀and RR₉₅) suggested that both vector species were susceptible to <it>Bti </it>(<it>Bacillus thuringiensis var israeliensis</it>) and temephos. Bioassays were also performed on adults using WHO diagnostic test kits to assess phenotypic resistance to deltamethrin, DDT, fenitrothion and propoxur. These experiments showed that one population of <it>Ae. aegypti </it>(Libreville) and two populations of <it>Ae. albopictus </it>(Buea and Yaoundé) were resistant to DDT (mortality 36% to 71%). Resistance to deltamethrin was also suspected in <it>Ae. albopictus </it>from Yaoundé (83% mortality). All other field mosquito populations were susceptible to deltamethrin, DDT, fenitrothion and propoxur. No increase in the knockdown times (Kdt₅₀and Kdt₉₅) was noted in the Yaoundé resistant population compared to other <it>Ae. albopictus </it>populations, suggesting the possible involvement of metabolic resistance to deltamethrin and DDT.</p> <p>Conclusion</p> <p>In view of the recent increase in dengue and chikungunya outbreaks in Central Africa, these unique comparative data on the insecticide susceptibility of <it>Ae. aegypti </it>and <it>Ae. albopictus </it>could help public health services to design more effective vector control measures.</p

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