Characterization of resistance profile (intensity and mechanisms) of Anopheles gambiae in three communes of northern Benin, West Africa

Background The selection and the spread of insecticide resistance in malaria vectors to the main classes of insecticides used in vector control tools are a major and ongoing challenge to malaria vector control programmes. This study aimed to determine the intensity of vector resistance to insecticides in three regions of Benin with different agro-ecological characteristics. Methods Larvae of Anopheles gambiae sensu lato (s.l.) were collected from September to November 2017 in different larval sites in three northern Benin communes: Parakou, Kandi and Malanville. Two to five-day-old, non-blood-fed, female mosquitoes were exposed to papers impregnated with deltamethrin, permethrin and bendiocarb at dosages of 1 × the diagnostic dose, 5 × and 10 × to determine the intensity of resistance in these vectors. Molecular frequencies of the kdr L1014F and ace-1R G119S insecticide resistance mutations and levels of detoxification enzymes were determined for mosquitoes sampled at each study site. Results Resistance to pyrethroids (permethrin and deltamethrin) was recorded in all three communes with mortality rates below 60% using the diagnostic dose (1x). The results obtained after exposure of An. gambiae to permethrin 10 × were 99% in Kandi, 98% in Malanville and 99% in Parakou. With deltamethrin 10x, mortality rates were 100% in Kandi, 96% in Malanville and 73% in Parakou. For the diagnostic dose of bendiocarb, suspected resistance was recorded in the communes of Malanville (97%) and Kandi (94%) while sensitivity was observed in Parakou (98%).Using the 10 × dose, mortality was 98% in Kandi, 100% in Malanville and 99% in Parakou. The frequencies of the kdr L1014F allele varied between 59 and 83% depending on the sites and species of the An. gambiae complex, while the frequency of the ace-1R G119S gene varied between 0 and 5%. Biochemical tests showed high levels of oxidase and esterase activity compared to the susceptible colony strain of An. gambiae sensu stricto (Kisumu strain). Conclusion Anopheles gambiae showed a generalized loss of susceptibility to permethrin and deltamethrin but also showed moderate to high intensity of resistance in different regions of Benin. This high intensity of resistance is a potential threat to the effectiveness of vector control.

Phenotypic Insecticide Resistance in Anopheles gambiae (Diptera: Culicidae): Specific Characterization of Underlying Resistance Mechanisms Still Matters

An effective control of malaria vectors requires an extensive knowledge of mechanisms underlying the resistance-phenotypes developed by these vectors against insecticides. We investigated Anopheles gambiae mosquitoes from Benin and Togo for their intensity of insecticide resistance and we discussed the involvement of genotyped mechanisms in the resistance-phenotypes observed. Three- to five-day-old adult mosquitoes emerged from field and laboratory An. gambiae larvae were assayed using WHO tube intensity tests against various doses of deltamethrin: 1× (0.05%); 2× (0.1%); 5× (0.25%); 7.5× (0.375%) and those of pirimiphos-methyl: 0.5× (0.125%); 1× (0.25%). Members of An. gambiae complex were screened in field populations using polymerase chain reaction (PCR) assays. The presence of kdrR(1014F/1014S) and ace-1R(119S) mutations was also investigated using TaqMan and PCR-RFLP techniques, respectively. Anopheles gambiae from field were very resistant to deltamethrin, whereas KisKdr and AcerKdrKis strains displayed 100% mortality rates at 2× the diagnostic dose. In contrast, the field mosquitoes displayed a low resistance-intensity against 1× the diagnostic dose of pirimiphos-methyl, whereas AcerKis and AcerKdrKis strains showed susceptibility at 0.5× the diagnostic dose. Anopheles gambiae s.s., Anopheles coluzzii, and Anopheles arabiensis were identified. Allelic frequencies of kdrR (1014F) and ace-1R (119S) mutations in the field populations varied from 0.65 to 1 and 0 to 0.84, respectively. The field An. gambiae displayed high-resistance levels against deltamethrin and pirimiphos-methyl when compared with those of the laboratory An. gambiae-resistant strains. These results exhibit the complexity of underlying insecticide resistance mechanisms in these field malaria vectors.

Intensity of pyrethroid resistance in Anopheles gambiae before and after a mass distribution of insecticide-treated nets in Kinshasa and in 11 provinces of the Democratic Republic of Congo

Background: Between 2011 and 2018, an estimated 134.8 million pyrethroid-treated long-lasting insecticidal nets (LLINs) were distributed nationwide in the Democratic Republic of Congo (DRC) for malaria control. Pyrethroid resistance has developed in DRC in recent years, but the intensity of resistance and impact on LLIN efficacy was not known. Therefore, the intensity of resistance of Anopheles gambiae sensu lato (s.l.) to permethrin and deltamethrin was monitored before and after a mass distribution of LLINs in Kinshasa in December 2016, and in 7 sites across the country in 2017 and 11 sites in 2018.Methods: In Kinshasa, CDC bottle bioassays using 1, 2, 5, and 10 times the diagnostic dose of permethrin and deltamethrin were conducted using An. gambiae s.l. collected as larvae and reared to adults. Bioassays were conducted in four sites in Kinshasa province six months before a mass distribution of deltamethrin-treated ITNs and then two, six, and ten months after the distribution. One site in neighbouring Kongo Central province was used as a control (no mass campaign of ITN distribution during the study). Nationwide intensity assays were conducted in six sites in 2017 using CDC bottle bioassays and in 11 sites in 2018 using WHO intensity assays. A sub-sample of An. gambiae s.l. was tested by PCR to determine species composition and frequency of kdr-1014F and 1014S alleles. Results: In June 2016, before LLIN distribution, permethrin resistance intensity was high in Kinshasa; the mean mortality rate was 43% at the 5× concentration and 73% at the 10× concentration. Bioassays at 3 time points after LLIN distribution showed considerable variation by site and time and there was no consistent evidence for an increase in pyrethroid resistance intensity compared to the neighbouring control site. Tests of An. gambiae s.l. in 7 sites across the country in 2017 and 11 sites in 2018 showed all populations were resistant to the diagnostic doses of 3 pyrethroids. In 2018, the intensity of resistance varied by site, but was generally moderate for all three pyrethroids, with survivors at ×5 the diagnostic dose. Anopheles gambiae sensu stricto (s.s.) was the most common species identified across 11 sites in DRC, but in Kinshasa, An. gambiae s.s. (91%) and Anopheles coluzzii (8%) were sympatric.Conclusions: Moderate or high intensity pyrethroid resistance was detected nationwide in DRC and is a serious threat to sustained malaria control with pyrethroid LLINs. Next generation nets (PBO nets or bi-treated nets) should be considered for mass distribution.

Intensity of pyrethroid resistance in An. gambiaes.l.before and after a mass distribution of insecticide treated nets in Kinshasa and from 11 provinces of the Democratic Republic of Congo

BackgroundBetween 2011 and 2018, an estimated 134.8 million pyrethroid-treatedlong-lasting insecticidal nets (LLINs) were distributed nationwide in the Democratic Republic of Congo (DRC) for malaria control. Pyrethroid resistance has developed in DRC in recent years, but the intensity ofresistance and impact on LLIN efficacy was not known. Therefore, the intensity of resistance of Anopheles gambiae s.l. to permethrin and deltamethrin was monitored before and after a mass distribution of LLINs in Kinshasa in December 2016, and in 7sites across the country in 2017 and 11 sites in 2018.Materials and MethodsIn Kinshasa, CDC bottle bioassays using 1, 2, 5, and 10 times the diagnostic dose of permethrin and deltamethrin were conducted using An. gambiae s.l. collected as larvae and reared to adults. Bioassays were conducted in four sites in Kinshasa province six months before a mass distribution of deltamethrin-treated ITNs and then two, six, and ten months after the distribution. One site in neighboring Kongo Central province was used as a control (no mass campaign of ITN distribution during the study). Nationwide intensity assays were conducted in six sites in 2017 using CDC bottle bioassays and in 11 sites in 2018 using WHO intensity assays. A sub-sample of An. gambiae s.l. were tested by PCR to determine species composition and frequency of kdr-1014F and 1014S alleles. ResultsIn June 2016, before LLIN distribution, permethrin resistance intensity was high in Kinshasa; the mean mortality rate was 43% at the 5× concentration and 73% at the 10× concentration. Bioassays at 3 time points after LLIN distribution showed considerable variation by site and time and there was no consistent evidence for an increase in pyrethroid resistance intensity compared to the neighboring control site. Tests of An. gambiaes.l. in 7 sites across the country in 2017 and 11 sites in 2018 showed all populations were resistant to the diagnostic doses of 3 pyrethroids.In 2018, the intensity of resistance varied by site, but was generally moderate for all three pyrethroids, with survivors at ×5 the diagnostic dose. An. gambiae s.s. was the most common species identified across 11 sites in DRC. However in Kinshasa, An. gambiae s.s.(91%) and An. coluzzii (8%) were sympatric.ConclusionsModerate or high intensity pyrethroid resistance was detected nationwide in DRC and is a serious threat to sustained malaria control with pyrethroid LLINs. Next generation nets (PBO nets or bi-treated nets) should be considered for mass distribution.

Permethrin Susceptibility for the Vector Culex tarsalis and a Nuisance Mosquito Aedes vexans in an Area Endemic for West Nile Virus

In 2016, we compared susceptibility to the insecticide, permethrin, between the West Nile virus vector, Culex tarsalis Coquillett, and a major nuisance mosquito, Aedes vexans (Meigen), using baseline diagnostic dose and time values determined using the CDC bottle bioassay protocol. Mosquitoes were collected in the wild in Brookings County, South Dakota, situated in the Northern Great Plains of the USA. The determined diagnostic dose and time were then used in 2017 to validate these measurements for the same 2 mosquito species, collected at a second location within Brookings County. The diagnostic dose was determined for multiple time periods and ranged from 27.0 µg/ml at 60 min to 38.4 µg/ml at 30 min. There was no significant difference detected in mortality rates between Cx. tarsalis and Ae. vexans for any diagnostic time and dose. For practical purposes, mosquitoes in 2017 were tested at 38 µg/ml for 30 min; expected mortality rates were 93.38% for Cx. tarsalis and 94.93% for Ae. vexans. Actual 2017 mortality rates were 92.68% for Cx. tarsalis and 96.12% for Ae. vexans, validating the usefulness of this baseline at an additional location and year.

Resistance Status of Aedes albopictus (Skuse) on Malathion in Bengkulu City

Dengue Hemorrhagic Fever (DHF) is a disease caused by dengue virus and transmitted by Aedes aegypti mosquito as the main vector and Aedes albopictus as secondary vector. In 2016, Bengkulu City was one of 3 cities that experiencing DHF outbreaks in Indonesia. Insecticides malathion have been used since 1990 in bulk in DHF control programs in Bengkulu City and have not had an evaluation report on Aedes sp. vulnerability to malathion. The purpose of this research was to know the resistance status of Ae albopictus mosquitoes from endemic and sporadic areas of DHF in Bengkulu City to malathion. The sample of the study was the Ae. albopictus adult female mosquitoes which collected from endemic and sporadic areas of DHF in Bengkulu City with ovitrap installation. The resistance test was performed by CDC Bottle Bioassay method with malation 96% and 50 μg/ml diagnostic dose of. The results of this study showed 1% mortality on endemic area and 5% on sporadic area. Aedes albopictus of both areas were resistant to malathion. Keywords: Ae. albopictus, bottle bioassay, malathion. Abstrak Demam Berdarah Dengue (DBD) merupakan penyakit yang disebabkan oleh virus dengue dan ditularkan oleh nyamuk Aedes aegypti sebagai vektor utama dan Aedes albopictus sebagai vektor sekunder. Pada tahun 2016, Kota Bengkulu merupakan 1 dari 3 kota yang mengalami KLB DBD di Indonesia. Insektisida malation telah digunakan sejak tahun 1990 secara massal dalam program pengendalian DBD di Kota Bengkulu dan belum memiliki laporan evaluasi mengenai kerentanan Aedes sp terhadap malation. Tujuan penelitian untuk mengetahui status kerentanan nyamuk Ae. albopictus dari daerah endemis dan sporadis DBD Kota Bengkulu terhadap malation. Sampel penelitian adalah nyamuk betina dewasa Ae. albopictus yang dikoleksi dari daerah endemik dan sporadis DBD Kota Bengkulu dengan pemasangan ovitrap. Uji kerentanan dilakukan dengan metode CDC Bottle Bioassay dengan malation 96% dan dosis diagnostik 50 µg/ml. Hasil penelitian ini menunjukkan mortalitas 1% untuk daerah endemis dan 5% untuk daerah sporadis. Aedes albopictus kedua daerah telah resisten terhadap malation. Kata Kunci: Ae. albopictus, bottle bioassay, malation.

Toxisitas temephos, minyak atsiri jahe ​(Zingiber officinale Roxb)​, dan ​Bacillus thuringiensis ssp. israelensis​ (Bti) terhadap larva nyamuk ​Ae. aegypti​ dari Sumatra Utara

Purpose: The purpose of this study was to confirm the resistance status and resistance ratio (RR) of Ae. aegypti larvae to temephos as well as to determine the effectiveness of a liquid solution of Bti H-14 and the essential oil of ginger (Zingiber officinale roxb) against Ae. aegypti larvae from Deli Serdang, North Sumatra.Method: A randomized post-test only control group was con- ducted using 3rd instar larvae of Ae. aegypti as the subjects of this study. Larval mortality was recorded after 24 hours of exposure with diagnostic dose of temephos (0.02ppm) to determine the resistance status. Probit analysis was conducted to determine median lethal time (LT50) and the RR. The concetration of Bti toxicity test was 0.01, 0.013, 0.017, 0.02, 0.03 and 0.04 mL/L and the concentration of toxicity essential oil of ginger test was 66.6, 99.9, 133.2, 166.5, 199.8 and 266.4 ppm.Results: Ae. aegypti larvae were resistant to temephos (0.02ppm) with RR 1.9 < 5. The value of LC50 and LC90 of Bti were 0.014; 0.024 mL/L respectively. The value of LC50 and LC90 of essential oil of ginger solution were 65.6ppm and 129.1ppm respectively.Conclusion: Larvae are resistant to temephos with low resistance criteria. Bti and essential oil of ginger are toxic to Ae. aegypti larvae.

Thyroid Remnant Estimation by Diagnostic DoseI131Scintigraphy orTcO4-99mScintigraphy after Thyroidectomy: A Comparison with Therapeutic DoseI131Imaging

In this clinical study, we have compared routine diagnostic dose131I scan andTcO4-99mthyroid scintigraphy with therapeutic dose131I imaging for accurate thyroid remnant estimation after total thyroidectomy. We conducted a retrospective review of the patients undergoing total thyroidectomy for differentiated thyroid carcinoma (DTC) and subsequently receiving radioactive iodine (RAI) treatment to ablate remnant thyroid tissue. All patients had therapeutic dose RAI whole body scan, which was compared with that of diagnostic dose RAI,TcO4-99mthyroid scan, and ultrasound examination. We concluded that therapeutic dose RAI scan reveals some extent thyroid remnant in all DTC patients following total thyroidectomy. Diagnostic RAI scan is much superior to ultrasound andTcO4-99mthyroid scan for the postoperative estimation of thyroid remnant. Ultrasound andTcO4-99mthyroid scan provide little information for thyroid remnant estimation and, therefore, would not replace diagnostic RAI scan.