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

A comparative study of carbohydrate antigen 19-9 in sickle cell disease subjects and controls in Nnamdi Azikiwe University Teaching Hospital, Nnewi, Nigeria

Background: Sickle cell disease is characterized by chronic complications that affect almost all body organs. Pancreatic disease is  rare in SCD. CA 19-9 is a non-specific surrogate marker for pancreatic disease especially carcinoma. CA 19-9 levels have not been evaluated in SCD patients in our environment.Objectives: The study aimed to compare the levels of CA 19-9 in homozygous sickle cell disease subjects in steady state with those of (Hb AS) and normal healthy subjects (Hb AA)Method: Seventy nine subjects including 39 Hb SS, 19 Hb AS and 21 Hb AA subjects were recruited in a cross-sectional study in Nnamdi Azikiwe University and Teaching Hospital.  Haemoglobin genotype and CA 19-9 estimation were done using Hb electrophoresis and enzyme linked immunosorbent assay respectively. Data was analyzed with IBM SPSS 21. P value was set at 0.05.Result: The mean CA 19-9 (U/ml) level in Hb SS, Hb AS and Hb AA were 13.6 ± 7.6, 15.3 ± 9.9, and 20.0 ± 15.9 respectively. [Reference value &lt;37U/ml] CA 19-9 was significantly lower in Hb SS compared to Hb AA subjects (p = 0.035). Conclusion: Low levels of CA 19-9 in Hb SS may suggest reduced pancreatic disorders in SCA. Keywords: Hemoglobin phenotype, disease severity, carbohydrate antigen 9-19, pancreatic disease, sickle cell disease

The cytochrome P450 CYP6P4 is responsible for the high pyrethroid resistance in knockdown resistance-free Anopheles arabiensis.

Pyrethroid insecticides are the front line vector control tools used in bed nets to reduce malaria transmission and its burden. However, resistance in major vectors such as Anopheles arabiensis is posing a serious challenge to the success of malaria control. Herein, we elucidated the molecular and biochemical basis of pyrethroid resistance in a knockdown resistance-free Anopheles arabiensis population from Chad, Central Africa. Using heterologous expression of P450s in Escherichia coli coupled with metabolism assays we established that the over-expressed P450 CYP6P4, located in the major pyrethroid resistance (rp1) quantitative trait locus (QTL), is responsible for resistance to Type I and Type II pyrethroid insecticides, with the exception of deltamethrin, in correlation with field resistance profile. However, CYP6P4 exhibited no metabolic activity towards non-pyrethroid insecticides, including DDT, bendiocarb, propoxur and malathion. Combining fluorescent probes inhibition assays with molecular docking simulation, we established that CYP6P4 can bind deltamethrin but cannot metabolise it. This is possibly due to steric hindrance because of the large vdW radius of bromine atoms of the dihalovinyl group of deltamethrin which docks into the heme catalytic centre. The establishment of CYP6P4 as a partial pyrethroid resistance gene explained the observed field resistance to permethrin, and its inability to metabolise deltamethrin probably explained the high mortality from deltamethrin exposure in the field populations of this Sudano-Sahelian An. arabiensis. These findings describe the heterogeneity in resistance towards insecticides, even from the same class, highlighting the need to thoroughly understand the molecular basis of resistance before implementing resistance management/control tools

A comparative study of carbohydrate antigen 19-9 in sickle cell disease subjects and controls in Nnamdi Azikiwe University Teaching Hospital, Nnewi, Nigeria

Background: Sickle cell disease is characterized by chronic complications that affect almost all body organs. Pancreatic disease is rare in SCD. CA 19-9 is a non-specific surrogate marker for pancreatic disease especially carcinoma. CA 19-9 levels have not been evaluated in SCD patients in our environment. Objectives: The study aimed to compare the levels of CA 19-9 in homozygous sickle cell disease subjects in steady state with those of (Hb AS) and normal healthy subjects (Hb AA) Method: Seventy nine subjects including 39 Hb SS, 19 Hb AS and 21 Hb AA subjects were recruited in a cross-sectional study in Nnamdi Azikiwe University and Teaching Hospital. Haemoglobin genotype and CA 19-9 estimation were done using Hb electrophoresis and enzyme linked immunosorbent assay respectively. Data was analyzed with IBM SPSS 21. P value was set at 0.05. Result: The mean CA 19-9 (U/ml) level in Hb SS, Hb AS and Hb AA were 13.6 \ub1 7.6, 15.3 \ub1 9.9, and 20.0 \ub1 15.9 respectively. [Reference value &lt;37U/ml] CA 19-9 was significantly lower in Hb SS compared to Hb AA subjects (p = 0.035). Conclusion: Low levels of CA 19-9 in Hb SS may suggest reduced pancreatic disorders in SCA

Pyrethroid and etofenprox resistance in Anopheles gambiae and Anopheles coluzzii from vegetable farms in Yaounde, Cameroon: dynamics, intensity and molecular basis

Previous studies have indicated widespread insecticide resistance in malaria vector populations from Cameroon. However, the intensity of this resistance and underlying mechanisms are poorly known. Therefore, we conducted three cross-sectional resistance surveys between April 2018 and October 2019, using the revised World Health Organization protocol, which includes resistance incidences and intensity assessments. Field-collected Anopheles gambiae s.l. populations from Nkolondom, Nkolbisson and Ekie vegetable farms in the city of Yaounde were tested with deltamethrin, permethrin, alpha-cypermethrin and etofenprox, using 1x insecticide diagnostic concentrations for resistance incidence, then 5x and 10x concentrations for resistance intensity. Subsamples were analyzed for species identification and the detection of resistance-associated molecular markers using TaqMan(R) qPCR assays. In Nkolbisson, both An. coluzzii (96%) and An. gambiae s.s. (4%) were found together, whereas only An. gambiae s.s. was present in Nkolondom, and only An. coluzzii was present in Ekie. All three populations were resistant to the four insecticides (<75% mortality rates-MR1x), with intensity generally fluctuating over the time between mod-erate ( /=98%-MR10x) and high (76-97%-MR10x). The kdr L995F, L995S, and N1570Y, and the Ace-1 G280S-resistant alleles were found in An. gambiae from Nkolondom, at 73%, 1%, 16% and 13% frequencies, respectively, whereas only the kdr L995F was found in An. gambiae s.s. from Nkolbisson at a 50% frequency. In An. coluzzii from Nkolbisson and Ekie, we detected only the kdr L995F allele at 65% and 60% frequencies, respectively. Furthermore, expression levels of Cyp6m2, Cyp9k1, and Gste2 metabolic genes were highly upregulated (over fivefold) in Nkolondom and Nkolbisson. Pyrethroid and etofenprox-based vector control interventions may be jeopardized in the prospected areas, due to high resistance intensity, with multiple mechanisms in An. gambiae s.s. and An. coluzzii

Fifteen Years of Annual Mass Treatment of Onchocerciasis with Ivermectin Have Not Interrupted Transmission in the West Region of Cameroon

We followed up the 1996 baseline parasitological and entomological studies on onchocerciasis transmission in eleven health districts in West Region, Cameroon. Annual mass ivermectin treatment had been provided for 15 years. Follow-up assessments which took place in 2005, 2006, and 2011 consisted of skin snips for microfilariae (mf) and palpation examinations for nodules. Follow-up Simulium vector dissections for larval infection rates were done from 2011 to 2012. mf prevalence in adults dropped from 68.7% to 11.4%, and nodule prevalence dropped from 65.9% to 12.1%. The decrease of mf prevalence in children from 29.2% to 8.9% was evidence that transmission was still continuing. mf rates in the follow-up assessments among adults and in children levelled out after a sharp reduction from baseline levels. Only three health districts out of 11 were close to interruption of transmission. Evidence of continuing transmission was also observed in two out of three fly collection sites that had infective rates of 0.19% and 0.18% and ATP of 70 (Foumbot) and 300 (Massangam), respectively. Therefore, halting of annual mass treatment with ivermectin cannot be done after 15 years as it might escalate the risk of transmission recrudescence

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

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