scholarly journals Resting Behavior of Malaria Vectors in Ghana and Its Implication on Vector Control.

2022 ◽  
Author(s):  
Akua Obeng Forson ◽  
Isaac A. Hinne ◽  
Shittu B. Dhikrullahi ◽  
Isaac Kwame Sr ◽  
Abdul Rahim Mohammed ◽  
...  
Keyword(s):  
Vector Control ◽  
Anopheles Gambiae ◽  
Blood Meal ◽  
Indoor Residual Spraying ◽  
Sub Saharan Africa ◽  
Malaria Vectors ◽  
Resistance Mutations ◽  
Sub Saharan ◽  
Outdoor Resting ◽  
Resting Behavior

Abstract Background: In Sub-Saharan Africa, there is widespread use of long-lasting insecticidal nets (LLINs) and Indoor residual spraying (IRS) to help control the density of malaria vectors and decrease the incidence of malaria in communities. An understanding of the interactions between increased insecticide use and resting behaviour patterns of malaria mosquitoes is important for an effective vector control programme. This study was carried out to investigate the resting behavior, host preference and infection with Plasmodium falciparum of malaria vectors in Ghana in the context of increasing insecticide resistance in malaria vectors in sub-saharan Africa.Methods: Indoor and outdoor resting Anopheline mosquitoes were sampled during the dry and rainy seasons in five sites that were in 3 ecological landscapes [Sahel savannah (Kpalsogou, Pagaza, Libga), Coastal savannah (Anyakpor) and Forest (Konongo) zones] using pyrethrum spray catches (PSC), mechanical aspiration (Prokopack) for indoor collections, pit shelter and Prokopack for outdoor collections. PCR based molecular diagnostics were used to determine mosquito speciation, genotype for knockdown resistance mutations (L1014S and L1014F), G119S Ace-1 mutation, specific host blood meal origins and sporozoite infection in field collected mosquitoes.Results: Anopheles gambiae s. l. was the predominant species (89.95%, n = 1,718), followed by An. rufipes (8.48%, n=162), and An. funestus s. l. (1.57%, n = 30). Sibling species of the Anopheles gambiae revealed An. coluzzii accounted for 63% (95% CI: 57.10 – 68.91), followed by An. gambiae s. s [27% (95% CI: 21.66 – 32.55)], and An. arabiensis [9% (95% CI: 6.22 – 13.57)]. The mean resting density of An. gambiae s. l. was higher outdoors (79.63%; 1,368/1,718) than indoors (20.37%; 350/1,718) (z = -4.815, p< 0.0001). The kdr west L1014F and the Ace-1 mutations were highest in indoor resting An. coluzzii and An. gambiae in the sahel-savannah sites compared to the forest and coastal savannah sites. Overall, the blood meal analyses revealed a large proportion of the malaria vectors preferred feeding on humans (70.2 %) than animals (29.8%) in all sites. The sporozoite rates was only detected in indoor resting An. coluzzii from the sahel savannah (5.0%) and forest (2.5%) zones.Conclusion: The study reports high outdoor resting densities of An. gambiae and An. coluzzii with high kdr west mutation frequencies, and persistence of malaria transmission indoors despite the use of LLINs and IRS. Continuous monitoring of changes in resting behavior of mosquitoes and implementation of complementary malaria control interventions are needed to target outdoor resting Anopheles mosquitoes in Ghana.

scholarly journals Insecticide resistance in indoor and outdoor-resting Anopheles gambiae s.l. in Northern Ghana

2020 ◽  
Author(s):  
Majidah Hamid-Adiamoh ◽  
Alfred Amambua-Ngwa ◽  
Davis Nwakanma ◽  
Umberto D’Alessandro ◽  
Gordon A. Awandare ◽  
...  
Keyword(s):  
Insecticide Resistance ◽  
Anopheles Gambiae ◽  
Blood Meal ◽  
Northern Ghana ◽  
Malaria Vectors ◽  
Glutathione S Transferase ◽  
Metabolic Resistance ◽  
Anopheles Gambiae S.L ◽  
Outdoor Resting ◽  
Resting Behavior

Abstract Background Selection pressure from continued exposure to insecticides drives the development of insecticide resistance and changes in resting behavior of malaria vectors, which may support residual transmission in several endemic settings. There is a need to understand how resistance drives changes in resting behavior within vector species. Here, we examined the association between insecticide resistance and resting behavior of Anopheles gambiae s.l. in Northern Ghana. Methods Adult mosquitoes were collected both indoors and outdoors from two communities using mouth aspirators and pit shelters. F1 progenies from a subset of mosquitoes were exposed to dichloro diphenyl trichloroethane (DDT), deltamethrin, malathion and bendiocarb using WHO insecticide susceptibility tests. Insecticide resistance markers including voltage-gated sodium channel (Vgsc)- 1014F, Vgsc-1014S, Vgsc-1575Y, glutathione-S-transferase epsilon 2 (GSTe2)-114T and acetylcholinesterase (Ace1)-119S, as well as blood meal sources were investigated using PCR methods. Activities of metabolic enzymes, acetylcholine esterase (AChE), non-specific β-esterases, glutathione-S-transferase (GST) and monooxygenases (oxidases) were measured from unexposed F1 progenies using microplate assays. Results Susceptibility of An. coluzzii to deltamethrin 24hr post-exposure was significantly higher in indoor (mortality=5%) than the outdoor (mortality=2.5%) populations (P=0.02). The mosquitoes were fully susceptible to malathion (mortality: indoor=98%, outdoor=100%). Susceptibility to DDT was significantly higher in outdoor (mortality=9%) than indoor (mortality=0%) mosquitoes (P=0.006). Mosquitoes were also found with suspected resistance to bendiocarb but mortality was not statistically different (mortality: indoor=90%, outdoor=95%. P=0.30). The frequencies of all resistance alleles were higher in F1 outdoor (0.11-0.85) than indoor (0.04-0.65) mosquito populations, while Vgsc-1014F in F0 An. gambiae s.s significantly associated with outdoor-resting behavior (P=0.01). Activities of non-specific β-esterase enzymes were significantly higher in outdoor than indoor mosquitoes (Mean enzyme activity: Outdoor=: 1.70/mg protein; Indoor=1.35/mg protein. P<0.0001). AChE activity was also more elevated in outdoor (0.62/mg protein) than indoor (0.57/mg protein) mosquitoes but this was not significant (P=0.08). Human blood index (HBI) was predominantly detected in indoor (18%) than the outdoor mosquito population (3%).Conclusions These findings revealed higher phenotypic resistance in indoor than outdoor-resting mosquitoes, but genotypic and metabolic resistance levels were higher in outdoor than the indoor mosquito populations. However, the overall results did not establish that there was a significant preference of resistant malaria vectors to solely rest indoors or outdoors, but varied depending on the resistant alleles present. Indication that human and animal blood meal indices were more prevalent in indoor-resting mosquitoes was also shown. Continued monitoring of changes in resting behavior within An. gambiae s.l. populations is recommended.

scholarly journals Insecticide resistance in indoor and outdoor-resting Anopheles gambiae s.l. in Northern Ghana

2020 ◽  
Author(s):  
Majidah Hamid-Adiamoh ◽  
Alfred Amambua-Ngwa ◽  
Davis Nwakanma ◽  
Umberto D’Alessandro ◽  
Gordon A. Awandare ◽  
...  
Keyword(s):  
Insecticide Resistance ◽  
Anopheles Gambiae ◽  
Blood Meal ◽  
Northern Ghana ◽  
Malaria Vectors ◽  
Glutathione S Transferase ◽  
Metabolic Resistance ◽  
Anopheles Gambiae S.L ◽  
Outdoor Resting ◽  
Resting Behavior

Abstract Background: Selection pressure from continued exposure to insecticides drives the development of insecticide resistance and changes in resting behavior of malaria vectors, which may support residual transmission in several endemic settings. There is a need to understand how resistance drives changes in resting behavior within vector species. Here, we examined the association between insecticide resistance and resting behavior of Anopheles gambiae s.l. in Northern Ghana. Methods: Adult mosquitoes were collected both indoors and outdoors from two communities using mouth aspirators and pit shelters. F1 progenies from a subset of mosquitoes were exposed to dichloro diphenyl trichloroethane (DDT), deltamethrin, malathion and bendiocarb using WHO insecticide susceptibility tests. Insecticide resistance markers including voltage-gated sodium channel (Vgsc)- 1014F, Vgsc-1014S, Vgsc-1575Y, glutathione-S-transferase epsilon 2 (GSTe2)-114T and acetylcholinesterase (Ace1)-119S, as well as blood meal sources were investigated using PCR methods. Activities of metabolic enzymes, acetylcholine esterase (AChE), non-specific β-esterases, glutathione-S-transferase (GST) and monooxygenases (oxidases) were measured from unexposed F1 progenies using microplate assays. Results: Susceptibility of An. coluzzii to deltamethrin 24hr post-exposure was significantly higher in indoor (mortality=5%) than the outdoor (mortality=2.5%) populations (P=0.02). The mosquitoes were fully susceptible to malathion (mortality: indoor=98%, outdoor=100%). Susceptibility to DDT was significantly higher in outdoor (mortality=9%) than indoor (mortality=0%) mosquitoes (P=0.006). Mosquitoes were also found with suspected resistance to bendiocarb but mortality was not statistically different (mortality: indoor=90%, outdoor=95%. P=0.30). The frequencies of all resistance alleles were higher in F1 outdoor (0.11-0.85) than indoor (0.04-0.65) mosquito populations, while Vgsc-1014F in F0 An. gambiae s.s significantly associated with outdoor-resting behavior (P=0.01). Activities of non-specific β-esterase enzymes were significantly higher in outdoor than indoor mosquitoes (Mean enzyme activity: Outdoor=: 1.70/mg protein; Indoor=1.35/mg protein. P<0.0001). AChE activity was also more elevated in outdoor (0.62/mg protein) than indoor (0.57/mg protein) mosquitoes but this was not significant (P=0.08). Human blood index (HBI) was predominantly detected in indoor (18%) than the outdoor mosquito population (3%). Conclusions: These findings revealed higher phenotypic resistance in indoor than outdoor-resting mosquitoes, but genotypic and metabolic resistance levels were higher in outdoor than the indoor mosquito populations. However, the overall results did not establish that there was a significant preference of resistant malaria vectors to solely rest indoors or outdoors, but varied depending on the resistant alleles present. Indication that human and animal blood meal indices were more prevalent in indoor-resting mosquitoes was also shown. Continued monitoring of changes in resting behavior within An. gambiae s.l. populations is recommended.

scholarly journals Molecular Detection of Insecticide Resistance Mutations in Anopheles gambiae from Sierra Leone Using Multiplex SNaPshot and Sequencing

2021 ◽  
Vol 11 ◽  
Author(s):  
Jianhai Yin ◽  
Frederick Yamba ◽  
Canjun Zheng ◽  
Shuisen Zhou ◽  
Samuel Juana Smith ◽  
...  
Keyword(s):  
Insecticide Resistance ◽  
Vector Control ◽  
Anopheles Gambiae ◽  
Sierra Leone ◽  
Statistical Significance ◽  
Indoor Residual Spraying ◽  
Malaria Vectors ◽  
Mosquito Vector ◽  
Resistance Mutations ◽  
African Countries

Vector control interventions including long-lasting insecticidal nets and indoor residual spraying are important for malaria control and elimination. And effectiveness of these interventions depends entirely on the high level of susceptibility of malaria vectors to insecticides. However, the insecticide resistance in majority of mosquito vector species across African countries is a serious threat to the success of vector control efforts with the extensive use of insecticides, while no data on insecticide resistance was reported from Sierra Leone in the past decade. In the present study, the polymerase chain reaction was applied for the identification of species of 757 dry adult female Anopheles gambiae mosquitoes reared from larvae collected from four districts in Sierra Leone during May and June 2018. And the mutations of kdr, rdl, ace-1 genes in An. gambiae were detected using SNaPshot and sequencing. As a result, one sample from Western Area Rural district belonged to Anopheles melas, and 748 An. gambiae were identified. Furthermore, the rdl mutations, kdr west mutations and ace-1 mutation were found. The overall frequency was 35.7%, 0.3%, 97.6% and 4.5% in A296G rdl, A296S rdl, kdrW and ace-1, respectively. The frequencies of A296G rdl mutation (P &lt; 0.001), kdrW mutation (P = 0.001) and ace-1 mutation (P &lt; 0.001) were unevenly distributed in four districts, respectively, while no statistical significance was found in A296S rdl mutation (P = 0.868). In addition, multiple resistance patterns were also found. In conclusion, multiple mutations involved in insecticide resistance in An. gambiae populations in Sierra Leone were detected in the kdrW, A296G rdl and ace-1 alleles in the present study. It is necessary to monitor vector susceptibility levels to insecticides used in this country, and update the insecticide resistance monitoring and management strategy.

scholarly journals Reduced human-biting preferences of the African malaria vectors Anopheles arabiensis and Anopheles gambiae in an urban context: controlled, competitive host-preference experiments in Tanzania

2020 ◽  
Author(s):  
Yeromin P Mlacha ◽  
Prosper P. Chaki ◽  
Athuman Muhili ◽  
Dennis J. Massue ◽  
Marcel Tanner ◽  
...  
Keyword(s):  
Vector Control ◽  
Anopheles Gambiae ◽  
Anopheles Arabiensis ◽  
Host Preference ◽  
Urban Setting ◽  
Sub Saharan Africa ◽  
Rural Setting ◽  
Malaria Vectors ◽  
Baited Traps ◽  
The Impact

Abstract BackgroundHost preference is a critical determinant of human exposure to vector-borne infections and the impact of vector control interventions. Widespread use of long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS) across sub-Saharan Africa, which protect humans against mosquitoes, may select for altered host preference traits of malaria vectors over the long term. Here, the host preferences of Anopheles arabiensis and Anopheles gambiae sensu stricto (s.s.) were experimentally assessed in the field, using direct host-preference assays in two distinct ecological settings in Tanzania.MethodsEight Ifakara Tent Trap (ITT), four baited with humans and four with bovine calves, were simultaneously used to catch malaria vectors in open field sites in urban and rural Tanzania. The numbers of mosquitoes collected in human-baited traps versus calf-baited traps were used to estimate human feeding preference for each site's vector species. ResultsThe estimated proportion [95% confidence interval (CI)] of mosquitoes attacking humans rather than cattle was 0.60 [0.40, 0.77] for An. arabiensis in the rural setting and 0.61 [0.32, 0.85] for An. gambiae s.s. in the urban setting, indicating no preference for either host in both cases (P=0.32 and 0.46, respectively) and no difference in preference between the two (Odds Ratio (OR) [95%] = 0.95 [0.30, 3.01], P=0.924). However, only a quarter of An. arabiensis in the urban setting attacked humans (0.25 [0.09, 0.53]), indicating a preference for cattle that approached significance (P=0.08). Indeed, urban An. arabiensis were less likely to attack humans rather than cattle when compared to the same species in the rural setting (OR [95%] = 0.21 [0.05, 0.91], P =0.037). ConclusionUrban An. arabiensis had a stronger preference for cattle than the rural population and urban An. gambiae s.s. showed no clear preference for either humans or cattle. In the urban setting, both species exhibited stronger tendencies to attack cattle than previous studies of the same species in rural contexts. Cattle keeping may, therefore, particularly limit the impact of human-targeted vector control interventions in Dar es Salaam and perhaps in other African towns and cities.

scholarly journals Reduced human-biting preferences by the African malaria vectors Anopheles arabiensis and Anopheles gambiae in an urban context: Controlled, competitive host-preference experiments in Tanzania

2020 ◽  
Author(s):  
Yeromin P Mlacha ◽  
Prosper P. Chaki ◽  
Athuman Muhili ◽  
Dennis J. Massue ◽  
Marcel Tanner ◽  
...  
Keyword(s):  
Anopheles Gambiae ◽  
Anopheles Arabiensis ◽  
Host Preference ◽  
Indoor Residual Spraying ◽  
Urban Setting ◽  
Sub Saharan Africa ◽  
Rural Setting ◽  
Malaria Vectors ◽  
Baited Traps ◽  
The Impact

Abstract BackgroundHost preference is a critical determinant of human exposure to vector-borne infections and also the impact of interventions. Widespread use of long-lasting insecticides treated nets (LLINs) and, indoor residual spraying (IRS) across sub-Saharan Africa, which protect humans against mosquitoes, may select for altered host preference traits of malaria vectors over the long term. Here, the host preferences of Anopheles arabiensis and Anopheles gambiae sensu stricto was experimentally assessed in the field, using direct host-preference assays in two distinct ecological settings in Tanzania. MethodsEight Ifakara Tent Trap (ITT), half of them baited with humans or bovine calves were simultaneously used to catch malaria vectors in open field sites urban and rural Tanzania. The numbers of mosquitoes collected in human-baited traps versus calf-baited traps were used to estimate human feeding preference of each malaria vector species present at each site. ResultsThe estimated proportion [95% confidence interval (CI)] of mosquitoes attacking humans rather than cattle was 0.60 [0.40, 0.77] for An. arabiensis in the rural setting and 0.61 [0.32, 0.85] for An. gambiae in the urban setting, indicating no preference for either host in both cases (P=0.32 and 0.46, respectively) and no difference in preference between the two (Odds Ratio (OR) [95%] = 0.95 [0.30, 3.01], P=0.924). However, only a quarter of An. arabiensis in the urban setting attacked humans (0.25 [0.09, 0.53]), indicating a preference for cattle that approached significance (P=0.08). Indeed, urban An. arabiensis were less likely to attack humans rather than cattle when compared to the same species in the rural setting (OR [95%] = 0.21 [0.05, 0.91], P =0.037). ConclusionUrban An. arabiensis had a stronger preference for cattle than the rural population in this or previous studies, all of which reported similar traits for this species in rural contexts. Furthermore, the urban An. gambiae assessed here had a weaker preference for humans over cattle than reported by previous studies of the same species in rural contexts. Cattle keeping may therefore particularly limit the impact of human-targeted vector control interventions in Dar es Salaam and perhaps in other African towns and cities.

Mosquitoes and Malaria Control – A Complex Problem for Entomologists to Unravel

2019 ◽  
Vol 30 (5) ◽  
pp. 213-216
Author(s):  
Basil Brooke
Keyword(s):  
Vector Control ◽  
Malaria Vector ◽  
Malaria Control ◽  
Life Stage ◽  
Indoor Residual Spraying ◽  
Transmission Intensity ◽  
Sub Saharan Africa ◽  
Malaria Vectors ◽  
Bed Nets ◽  
Vector Species

The control of malaria transmitting mosquitoes hinges on accurate species identification. This enables assessments of insecticide susceptibilities and important behavioural characteristics (such as feeding and resting behaviours) by species, leading to the design of coherent insecticide-based control strategies that can be enhanced by additional methodologies for malaria elimination. Malaria is a mosquito-borne parasitic disease that affects many vertebrates including humans. Prior to the 20th century the human malarias (Plasmodium falciparum, P. vivax, P. malariae, P. ovale and P. knowlesi) occurred in tropical and temperate regions but their distribution has since reduced to the tropical belt with by far the highest incidence in sub-Saharan Africa. Global incidence for 2017 was estimated by the WHO at 219 million cases corresponding to 435 000 deaths. It is also estimated that investment in malaria control and elimination amounted to $3.1 billion in 2017. The control (and elimination) of malaria largely hinges on the suppression of mosquito vectors, accurate diagnosis and case detection, and case management using appropriate antimalarial drug regimens. Controlling malaria vector mosquitoes (and of course other mosquito-borne diseases) means being able to identify that which needs to be controlled. This is not unlike the maxim of knowing one's enemy, and disease vector control is often phrased in militaristic terms. The arsenal of tools in the war against malaria vectors includes insecticides, bed nets, repellents, larvicides, endectocides, toxic baits and even modified genes. This call to arms against the transmitters of a deadly disease presupposes that the enemy can be identified, which, unfortunately, is not as easy as it sounds. Identifying malaria vectors to species has posed a significant challenge ever since Ronald Ross and Giovanni Grassi implicated dappled-winged Anopheles mosquitoes in malaria transmission. They could not have known the Pandora's Box they had opened, because several Anopheles species are cryptic. Many hide in cryptic species complexes and groups that confound straightforward morphological methods of identifying them. A species complex is a group of morphologically identical species that are very closely related, but nevertheless vary significantly in their feeding and resting behaviours, and mate assortatively (i.e. they recognise and tend only to mate with conspecific partners) enough that hybridisations between them are rare. Many member species of these complexes are sufficiently diverged that cross-mating between them yields infertile or non-viable offspring, but not in all cases. A species group is a looser assortment of related species whose morphological features match to a point where they are very nearly identical, often requiring specimens from more than one life stage to identify them. They also mate assortatively, and hybrids are rarer or simply never occur. The problem for malaria control is that several vector species, including many primary vectors, are members of cryptic complexes or groups. These invariably contain vector and non-vector species, requiring a complex and laborious system to unravel them and ascribe unambiguous genetic methods for their identification. Added to this complexity is the possibility that any Anopheles. species that takes human blood is a potential vector of the human malarias, with the added caveat that not all populations within a species are vectors. Some member species, and even populations within a species, feed either exclusively on humans (anthropophagy) and are potentially high transmission intensity vectors, or exclusively on livestock animals (zoophagy) making them non-vectors, or take blood from a range of sources including humans, becoming potential vectors of low to medium transmission intensity. An added layer of complexity is genetic heterogeneity between populations within a species. It can be argued that this complexity is not necessarily a problem for malaria control. After all, the aim of suppressing or even eliminating vector populations is the interruption of transmission, regardless of what species they are. But mosquito adaptability dictates otherwise. This is because the primary method of malaria vector control is deployment of specially formulated insecticides against adult mosquitoes, either by indoor residual spraying (IRS) or the treatment of bed nets. Mosquito adaptability has enabled a powerful response to these interventions, with resistance to insecticides becoming so widespread that fully insecticide susceptible malaria vector populations are now quite rare.

scholarly journals Reduced human-biting preferences of the African malaria vectors Anopheles arabiensis and Anopheles gambiae in an urban context: controlled, competitive host-preference experiments in Tanzania

2020 ◽  
Vol 19 (1) ◽  
Author(s):  
Yeromin P. Mlacha ◽  
Prosper P. Chaki ◽  
Athuman Muhili ◽  
Dennis J. Massue ◽  
Marcel Tanner ◽  
...  
Keyword(s):  
Vector Control ◽  
Anopheles Gambiae ◽  
Anopheles Arabiensis ◽  
Host Preference ◽  
Urban Setting ◽  
Sub Saharan Africa ◽  
Rural Setting ◽  
Malaria Vectors ◽  
Baited Traps ◽  
The Impact

Abstract Background Host preference is a critical determinant of human exposure to vector-borne infections and the impact of vector control interventions. Widespread use of long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS) across sub-Saharan Africa, which protect humans against mosquitoes, may select for altered host preference traits of malaria vectors over the long term. Here, the host preferences of Anopheles arabiensis and Anopheles gambiae sensu stricto (s.s.) were experimentally assessed in the field, using direct host-preference assays in two distinct ecological settings in Tanzania. Methods Eight Ifakara Tent Trap (ITT), four baited with humans and four with bovine calves, were simultaneously used to catch malaria vectors in open field sites in urban and rural Tanzania. The numbers of mosquitoes collected in human-baited traps versus calf-baited traps were used to estimate human feeding preference for each site's vector species. Results The estimated proportion [95% confidence interval (CI)] of mosquitoes attacking humans rather than cattle was 0.60 [0.40, 0.77] for An. arabiensis in the rural setting and 0.61 [0.32, 0.85] for An. gambiae s.s. in the urban setting, indicating no preference for either host in both cases (P = 0.32 and 0.46, respectively) and no difference in preference between the two (Odds Ratio (OR) [95%] = 0.95 [0.30, 3.01], P = 0.924). However, only a quarter of An. arabiensis in the urban setting attacked humans (0.25 [0.09, 0.53]), indicating a preference for cattle that approached significance (P = 0.08). Indeed, urban An. arabiensis were less likely to attack humans rather than cattle when compared to the same species in the rural setting (OR [95%] = 0.21 [0.05, 0.91], P = 0.037). Conclusion Urban An. arabiensis had a stronger preference for cattle than the rural population and urban An. gambiae s.s. showed no clear preference for either humans or cattle. In the urban setting, both species exhibited stronger tendencies to attack cattle than previous studies of the same species in rural contexts. Cattle keeping may, therefore, particularly limit the impact of human-targeted vector control interventions in Dar es Salaam and perhaps in other African towns and cities.

scholarly journals Determination of the discriminating concentration of chlorfenapyr (pyrrole) and Anopheles gambiae sensu lato susceptibility testing in preparation for distribution of Interceptor® G2 insecticide-treated nets

2021 ◽  
Vol 20 (1) ◽  
Author(s):  
Richard M. Oxborough ◽  
Aklilu Seyoum ◽  
Yemane Yihdego ◽  
Joseph Chabi ◽  
Francis Wat’senga ◽  
...  
Keyword(s):  
Anopheles Gambiae ◽  
Large Scale ◽  
Resistance Mechanisms ◽  
Probit Analysis ◽  
Sub Saharan Africa ◽  
Malaria Vectors ◽  
Insecticide Treated Nets ◽  
Distributed Testing ◽  
The Difference ◽  
Sub Saharan

Abstract Background Following agricultural use and large-scale distribution of insecticide-treated nets (ITNs), malaria vector resistance to pyrethroids is widespread in sub-Saharan Africa. Interceptor® G2 is a new dual active ingredient (AI) ITN treated with alpha-cypermethrin and chlorfenapyr for the control of pyrethroid-resistant malaria vectors. In anticipation of these new nets being more widely distributed, testing was conducted to develop a chlorfenapyr susceptibility bioassay protocol and gather susceptibility information. Methods Bottle bioassay tests were conducted using five concentrations of chlorfenapyr at 12.5, 25, 50, 100, and 200 µg AI/bottle in 10 countries in sub-Saharan Africa using 13,639 wild-collected Anopheles gambiae sensu lato (s.l.) (56 vector populations per dose) and 4,494 pyrethroid-susceptible insectary mosquitoes from 8 colonized strains. In parallel, susceptibility tests were conducted using a provisional discriminating concentration of 100 µg AI/bottle in 16 countries using 23,422 wild-collected, pyrethroid-resistant An. gambiae s.l. (259 vector populations). Exposure time was 60 min, with mortality recorded at 24, 48 and 72 h after exposure. Results Median mortality rates (up to 72 h after exposure) of insectary colony mosquitoes was 100% at all five concentrations tested, but the lowest dose to kill all mosquitoes tested was 50 µg AI/bottle. The median 72-h mortality of wild An. gambiae s.l. in 10 countries was 71.5, 90.5, 96.5, 100, and 100% at concentrations of 12.5, 25, 50, 100, and 200 µg AI/bottle, respectively. Log-probit analysis of the five concentrations tested determined that the LC95 of wild An. gambiae s.l. was 67.9 µg AI/bottle (95% CI: 48.8–119.5). The discriminating concentration of 203.8 µg AI/bottle (95% CI: 146–359) was calculated by multiplying the LC95 by three. However, the difference in mortality between 100 and 200 µg AI/bottle was minimal and large-scale testing using 100 µg AI/bottle with wild An. gambiae s.l. in 16 countries showed that this concentration was generally suitable, with a median mortality rate of 100% at 72 h. Conclusions This study determined that 100 or 200 µg AI/bottle chlorfenapyr in bottle bioassays are suitable discriminating concentrations for monitoring susceptibility of wild An. gambiae s.l., using mortality recorded up to 72 h. Testing in 16 countries in sub-Saharan Africa demonstrated vector susceptibility to chlorfenapyr, including mosquitoes with multiple resistance mechanisms to pyrethroids.

scholarly journals Associated patterns of insecticide resistance in field populations of malaria vectors across Africa

2018 ◽  
Vol 115 (23) ◽  
pp. 5938-5943 ◽  
Author(s):  
Penelope A. Hancock ◽  
Antoinette Wiebe ◽  
Katherine A. Gleave ◽  
Samir Bhatt ◽  
Ewan Cameron ◽  
...  
Keyword(s):  
Insecticide Resistance ◽  
Vector Control ◽  
Mosquito Species ◽  
Quantitative Information ◽  
Sub Saharan Africa ◽  
Malaria Vectors ◽  
Cross Resistance ◽  
Resistance Patterns ◽  
Geostatistical Models ◽  
Sub Saharan

The development of insecticide resistance in African malaria vectors threatens the continued efficacy of important vector control methods that rely on a limited set of insecticides. To understand the operational significance of resistance we require quantitative information about levels of resistance in field populations to the suite of vector control insecticides. Estimation of resistance is complicated by the sparsity of observations in field populations, variation in resistance over time and space at local and regional scales, and cross-resistance between different insecticide types. Using observations of the prevalence of resistance in mosquito species from the Anopheles gambiae complex sampled from 1,183 locations throughout Africa, we applied Bayesian geostatistical models to quantify patterns of covariation in resistance phenotypes across different insecticides. For resistance to the three pyrethroids tested, deltamethrin, permethrin, and λ-cyhalothrin, we found consistent forms of covariation across sub-Saharan Africa and covariation between resistance to these pyrethroids and resistance to DDT. We found no evidence of resistance interactions between carbamate and organophosphate insecticides or between these insecticides and those from other classes. For pyrethroids and DDT we found significant associations between predicted mean resistance and the observed frequency of kdr mutations in the Vgsc gene in field mosquito samples, with DDT showing the strongest association. These results improve our capacity to understand and predict resistance patterns throughout Africa and can guide the development of monitoring strategies.

scholarly journals Evolution of the Pyrethroids Target-Site Resistance Mechanisms in Senegal: Early Stage of the Vgsc-1014F and Vgsc-1014S Allelic Frequencies Shift

Genes ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1948
Author(s):  
Moussa Diallo ◽  
Majidah Hamid-Adiamoh ◽  
Ousmane Sy ◽  
Pape Cheikh Sarr ◽  
Jarra Manneh ◽  
...  
Keyword(s):  
Insecticide Resistance ◽  
Anopheles Gambiae ◽  
Pyrethroid Resistance ◽  
Early Stage ◽  
Resistance Mechanisms ◽  
Sub Saharan Africa ◽  
Malaria Vectors ◽  
Malaria Control Programme ◽  
Anopheles Coluzzii ◽  
Resistance Mutations

The evolution and spread of insecticide resistance mechanisms amongst malaria vectors across the sub-Saharan Africa threaten the effectiveness and sustainability of current insecticide-based vector control interventions. However, a successful insecticide resistance management plan relies strongly on evidence of historical and contemporary mechanisms circulating. This study aims to retrospectively determine the evolution and spread of pyrethroid resistance mechanisms among natural Anopheles gambiae s.l. populations in Senegal. Samples were randomly drawn from an existing mosquito sample, collected in 2013, 2017, and 2018 from 10 sentinel sites monitored by the Senegalese National Malaria Control Programme (NMCP). Molecular species of An. gambiae s.l. and the resistance mutations at the Voltage-gated Sodium Channel 1014 (Vgsc-1014) locus were characterised using PCR-based assays. The genetic diversity of the Vgsc gene was further analyzed by sequencing. The overall species composition revealed the predominance of Anopheles arabiensis (73.08%) followed by An. gambiae s.s. (14.48%), Anopheles coluzzii (10.94%) and Anopheles gambiae–coluzii hybrids (1.48%). Both Vgsc-1014F and Vgsc-1014S mutations were found in all studied populations with a spatial variation of allele frequencies from 3% to 90%; and 7% to 41%, respectively. The two mutations have been detected since 2013 across all the selected health districts, with Vgsc-L1014S frequency increasing over the years while Vgsc-1014F decreasing. At species level, the Vgsc-1014F and Vgsc-1014S alleles were more frequent amongst An. gambiae s.s. (70%) and An. arabiensis (20%). The Vgsc gene was found to be highly diversified with eight different haplotypes shared between Vgsc-1014F and Vgsc-1014S. The observed co-occurrence of Vgsc-1014F and Vgsc-1014S mutations suggest that pyrethroid resistance is becoming a widespread phenomenon amongst malaria vector populations, and the NMCP needs to address this issue to sustain the gain made in controlling malaria.

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