Four years trends of malaria admissions in rural and urban Kandi health facilities in northeast of Benin Republic

Malaria clinical data from health facility records are used for evaluating control programmes’ impact and providing insights of epidemiological situation. In the present study we assessed trend of malaria admissions between 2009 and 2012 in rural and urban health facilities of the district of Kandi, a very arid area with particularly severe drought lasting up to 6 months. Curative care records in the Gansosso urban health facility and Sonsoro rural health facility were consulted and all uncomplicated and severe cases of malaria in local population between 2009 and 2012 were reported. For each malaria case, information on age, gender, origin of the patient were collected on electronic forms using tablets installed with Open Data Kit (ODK) Collect. Characteristics of patients positive to malaria, change in age groups and monthly variation were compared between the urban and rural health facilities. Of the 21,008 febrile patients consulted, a total of 7,990 cases (38%; 95% CI 37-39) were detected positive to malaria by the means of RDTs or microscopy. The number of confirmed malaria cases in rural and urban Kandi were respectively 2,911 (36%, 95% CI 35-37) and 5,079 (39%, 95% CI 38-40) (p<0.001). Severe cases were recorded at a lower frequency in the rural health facility, as compared to the urban one (1% vs 25%, p<0.001) with most of cases diagnosed in patients from neighbouring villages. Both facilities records showed higher prevalence in females as compared to males (51% vs 49%; p =0.97). At rural Kandi, the age group hardest hit was under 5 years representing 40% (95% CI: 38-42) while in urban Kandi, malaria prevalence was higher in the age group older than 15 years (53%; 95% CI: 52-54). Between 2009 and 2012, monthly malaria prevalence was generally higher in rural areas than in urban ones. Except for 2012, peaks of malaria cases occurred earlier in the rural area than in the urban area. Our study indicated that malaria occurs throughout the year, regardless of the seasons, and affected all age groups in both rural and urban localities. This is of a programmatic interest in designing and planning vector control interventions particularly in endemic settings

Seasonal change in species composition and target-site mutations in Anopheles gambiae s.l. in the severe drought area of Kandi, North-eastern Benin

The persistence of malaria transmission in areas with very arid environmental conditions remains enigmatic. The present study investigated seasonal variation of mosquito species composition and Kdr and Ace-1 mutations in Anopheles gambiae s.l. in the very arid district of Kandi in North-eastern Benin.Adult mosquitoes were sampled over 1 year using both human landing catches (HLC) and pyrethrum spray catches in 4 villages belonging to 2 areas of different levels of aridity. The collections were carried out on a bi-monthly basis in the wet season, and once every month in the dry season to better capture the entomological situation in drought period. Females An. gambiae sl specimens were kept aside and analysed by PCR for species identification. Presence of kdr and Ace-1 mutations was also assessed in the An. gambiae s.l. collection.A total of 2,211 host-seeking mosquitoes belonging to 15 species were collected in the study area. An. gambiae s.l. was the most abundant species and represented 67% of the collection. Other Anopheles species were found at very low frequency among which An. funestus, An. pharoensis, An. broheri and An. coustani. Molecular species identification showed in dry season a significantly higher frequency of An. coluzzii over An. gambiae s. s. in both less dry (70% vs 29% with p < 0.001) and driest (70% vs 30% and p = 0.034) areas of the district of Kandi. In the rainy season, there was similar frequency of An. coluzzii and An. gambiae s. s. in the less arid area (53% vs 45%; p = 0.153), while An. coluzzii remained significantly predominant (62% vs 38%; p = 0.012) in the driest zone. The frequency of kdr mutation was significantly higher in dry season than in rainy season (93% vs 84%; p<0.001), while no Ace-1 mutation was detected in the collection.In the current context of climate change marked by increasingly high temperatures and longer droughts, suitable vector control should be designed taking into account characteristics of the vector population maintaining malaria transmission in such arid environmental conditions

Efficacy of broflanilide (VECTRON T500), a new meta-diamide insecticide, for indoor residual spraying against pyrethroid-resistant malaria vectors.

The rotational use of insecticides with different modes of action for indoor residual spraying (IRS) is recommended for improving malaria vector control and managing insecticide resistance. Insecticides with new chemistries are urgently needed. Broflanilide is a newly discovered insecticide under consideration. We investigated the efficacy of a wettable powder (WP) formulation of broflanilide (VECTRON T500) for IRS on mud and cement wall substrates in laboratory and experimental hut studies against pyrethroid-resistant malaria vectors in Benin, in comparison with pirimiphos-methyl CS (Actellic 300CS). There was no evidence of cross-resistance to pyrethroids and broflanilide in CDC bottle bioassays. In laboratory cone bioassays, broflanilide WP-treated substrates killed > 80% of susceptible and pyrethroid-resistant An. gambiae sl for 6-14 months. At application rates of 100 mg/m2 and 150 mg/m2, mortality of wild pyrethroid-resistant An. gambiae sl entering experimental huts in Covè, Benin treated with VECTRON T500 was similar to pirimiphos-methyl CS (57-66% vs. 56%, P > 0.05). Throughout the 6-month hut trial, monthly wall cone bioassay mortality on VECTRON T500 treated hut walls remained > 80%. IRS with broflanilide shows potential to significantly improve the control of malaria transmitted by pyrethroid-resistant mosquito vectors and could thus be a crucial addition to the current portfolio of IRS insecticides

Which indoor residual spraying insecticide best complements standard pyrethroid long-lasting insecticidal nets for improved control of pyrethroid resistant malaria vectors?

BACKGROUND: Where resources are available, non-pyrethroid IRS can be deployed to complement standard pyrethroid LLINs with the aim of achieving improved vector control and managing insecticide resistance. The impact of the combination may however depend on the type of IRS insecticide deployed. Studies comparing combinations of pyrethroid LLINs with different types of non-pyrethroid IRS products will be necessary for decision making. METHODS: The efficacy of combining a standard pyrethroid LLIN (DuraNet®) with IRS insecticides from three chemical classes (bendiocarb, chlorfenapyr and pirimiphos-methyl CS) was evaluated in an experimental hut trial against wild pyrethroid-resistant Anopheles gambiae s.l. in Cové, Benin. The combinations were also compared to each intervention alone. WHO cylinder and CDC bottle bioassays were performed to assess susceptibility of the local An. gambiae s.l. vector population at the Cové hut site to insecticides used in the combinations. RESULTS: Susceptibility bioassays revealed that the vector population at Cové, was resistant to pyrethroids (<20% mortality) but susceptible to carbamates, chlorfenapyr and organophosphates (≥98% mortality). Mortality of wild free-flying pyrethroid resistant An. gambiae s.l. entering the hut with the untreated net control (4%) did not differ significantly from DuraNet® alone (8%, p = 0.169). Pirimiphos-methyl CS IRS induced the highest mortality both on its own (85%) and in combination with DuraNet® (81%). Mortality with the DuraNet® + chlorfenapyr IRS combination was significantly higher than each intervention alone (46% vs. 33% and 8%, p<0.05) demonstrating an additive effect. The DuraNet® + bendiocarb IRS combination induced significantly lower mortality compared to the other combinations (32%, p<0.05). Blood-feeding inhibition was very low with the IRS treatments alone (3-5%) but increased significantly when they were combined with DuraNet® (61% - 71%, p<0.05). Blood-feeding rates in the combinations were similar to the net alone. Adding bendiocarb IRS to DuraNet® induced significantly lower levels of mosquito feeding compared to adding chlorfenapyr IRS (28% vs. 37%, p = 0.015). CONCLUSIONS: Adding non-pyrethroid IRS to standard pyrethroid-only LLINs against a pyrethroid-resistant vector population which is susceptible to the IRS insecticide, can provide higher levels of vector mosquito control compared to the pyrethroid net alone or IRS alone. Adding pirimiphos-methyl CS IRS may provide substantial improvements in vector control while adding chlorfenapyr IRS can demonstrate an additive effect relative to both interventions alone. Adding bendiocarb IRS may show limited enhancements in vector control owing to its short residual effect

Anopheles stephensi: The emerging vector of malaria in the Republic of Djibouti, Horn of Africa

The present study investigated mosquito species composition and phenotypic insecticide resistance profile to support decision-making in vector control in the Republic of Djibouti at the Horn of Africa. Adult mosquitoes were collected between December 2016 and December 2017 across 20 sentinel sites established in the 6 regions of the country using both Centers for Disease Control (CDC) miniature light traps and pyrethrum spray catches (PSC). Female mosquitoes were kept aside, for morphological identification to species by an expert entomologist using appropriate taxonomic keys by Gillies & Coetzee and Glick. Bioassays were also conducted in An. stephensi from Djibouti-ville against nine insecticides used in public health. A total number of 12,538 host-seeking mosquitoes belonging to four genera (Anopheles, Culex, Aedes, Uranotaenia) comprising 12 species were collected. Among these, A. gambiae S.L. and A. stephensi were the two major malaria vectors identified while secondary malaria vectors such as A. nili somalicus, A. dthali and A. azaniae were also collected. Culex quinquefasciatus was the most abundant mosquito species in the 6 regions. WHO susceptibility tests performed on A. stephensi population from Djibouti-ville showed resistance to pyrethroids, organophosphates, carbamates and DDT. The resistance intensity bioassays indicated low to moderate intensity of resistance with pyrethroid insecticides and the organophosphate pirimiphos methyl. Meanwhile pre-exposure to PBO suggested involvement of P450 detoxification enzymes in pyrethroid resistance. These findings revealed the urgent need to develop and implement a programme for monitoring and managing insecticide resistance in local vector populations with efficient control strategies in Djibouti

Community evaluation of the physical and insecticidal durability of DuraNet® Plus, an alpha-cypermethrin and piperonyl butoxide incorporated mosquito net: protocol for a multi-country study in West, Central and East Africa

Background: Pyrethroid-PBO nets have demonstrated improved impact against clinical malaria transmitted by pyrethroid resistant mosquito vectors and are being scaled up across Africa. However very little is known about their physical and insecticidal durability under operational conditions. This study will investigate the attrition, fabric integrity, insecticide content and bioefficacy of DuraNet® Plus, a new WHO prequalified alphacypermethrin and PBO incorporated net developed by Shobikaa Impex Private Limited over 3 years of field use in communities in Benin, Cameroon and Tanzania. Methods: The study will be conducted in parallel in selected villages in Zakpota District in Benin, Mbalmayo, District in Cameroon and Muheza District in Tanzania. In each country, ~ 1800 households will be recruited and randomised to receive DuraNet® Plus or DuraNet® (a WHO prequalified alphacypermethrin-only ITN). Follow up surveys will be performed at 1 month post distribution to investigate adverse events and subsequently every 6–12 months to assess ITN attrition and fabric integrity following standard WHO procedures. A second cohort of nets will be withdrawn every 6–12 months and assessed for alpha-cypermethrin and PBO content and for entomological activity in laboratory bioassays (cone bioassays and tunnel tests). Alpha-cypermethrin bioefficacy will be monitored using the susceptible Anopheles gambiae Kisumu strain in cone bioassays while PBO bioefficacy will be monitored using pyrethroid resistant strains with overexpressed P450 enzymes in tunnel tests to determine the proportion of efficacious nets (≥ 95% knockdown, ≥ 80% mortality or ≥ 90% blood feeding inhibition in tunnels) at each time point. Nets withdrawn at 12, 24 and 36 months from each country will also be tested in experimental hut trials against wild free-flying pyrethroid resistant Anopheles gambiae sl in Côvè Benin to investigate the superiority of DuraNet® Plus over DuraNet® at each time point under semi field conditions. Conclusion: This large-scale multi country trial will provide useful information on the durability of a pyrethroid-PBO net (DuraNet® Plus) in 3 different regions in sub-Saharan Africa. The methods proposed for bioefficacy testing could also contribute towards the development of new standardised guidelines for monitoring the insecticidal efficacy of pyrethroid-PBO nets under operational conditions

The effects of oviposition site deprivation up to 40 days on reproductive performance, eggs development, and ovipositional behaviour in Anopheles gambiae (Diptera, Nematocera, Culicidae)

The African malaria mosquito, Anopheles gambiae, depends on availability of suitable surface water for oviposition. The scarcity of breeding sites that characterizes droughts force gravid mosquitoes to delay oviposition and retain eggs in their ovaries. In laboratory conditions, we explored the possible consequences of preset duration of oviposition delay on reproductive capacity, egg viability, emergence and ovipositional behavior in gravid females of A. gambiae waiting for eggs laying in a context of oviposition delay. Overall, the mean anopheles egg batch size was not affected by the duration of the oviposition site deprivation. The embryo rates, hatchability and emergence rates decreased significantly gradually as the retention time is extended. However, the oviposition site deprivation has not been identified as a factor that can change the behavior of Anopheles in their choice of oviposition site

Evidence of multiple insecticide resistance mechanisms in Anopheles gambiae populations in Bangui, Central African Republic

Number of Anopheles (%) tested by bioassays in seven sites of Bangui, Central African Republic by using WHO test kits for adult mosquitoes. Six insecticides of technical grade were used, including two pyrethroids (deltamethrin and lambda-cyhalothrin), one carbamate (bendiocarb), two organophosphates (fenitrothion and malathion) and one organochlorine (DDT). (XLSX 15 kb

VECTRON™ T500, a new broflanilide insecticide for indoor residual spraying, provides prolonged control of pyrethroid-resistant malaria vectors.

BACKGROUND: Broflanilide is a newly discovered insecticide with a novel mode of action targeting insect γ-aminobutyric acid receptors. The efficacy of VECTRON™ T500, a wettable powder formulation of broflanilide, was assessed for IRS against wild pyrethroid-resistant malaria vectors in experimental huts in Benin. METHODS: VECTRON™ T500 was evaluated at 100 mg/m2 in mud and cement-walled experimental huts against wild pyrethroid-resistant Anopheles gambiae sensu lato (s.l.) in Covè, southern Benin, over 18 months. A direct comparison was made with Actellic® 300CS, a WHO-recommended micro-encapsulated formulation of pirimiphos-methyl, applied at 1000 mg/m2. The vector population at Covè was investigated for susceptibility to broflanilide and other classes of insecticides used for vector control. Monthly wall cone bioassays were performed to assess the residual efficacy of VECTRON™ T500 using insecticide susceptible An. gambiae Kisumu and pyrethroid-resistant An. gambiae s.l. Covè strains. The study complied with OECD principles of good laboratory practice. RESULTS: The vector population at Covè was resistant to pyrethroids and organochlorines but susceptible to broflanilide and pirimiphos-methyl. A total of 23,171 free-flying wild pyrethroid-resistant female An. gambiae s.l. were collected in the experimental huts over 12 months. VECTRON™ T500 induced 56%-60% mortality in wild vector mosquitoes in both cement and mud-walled huts. Mortality with VECTRON™ T500 was 62%-73% in the first three months and remained > 50% for 9 months on both substrate-types. By comparison, mortality with Actellic® 300CS was very high in the first three months (72%-95%) but declined sharply to < 40% after 4 months. Using a non-inferiority margin defined by the World Health Organization, overall mortality achieved with VECTRON™ T500 was non-inferior to that observed in huts treated with Actellic® 300CS with both cement and mud wall substrates. Monthly in situ wall cone bioassay mortality with VECTRON™ T500 also remained over 80% for 18 months but dropped below 80% with Actellic® 300CS at 6-7 months post spraying. CONCLUSION: VECTRON™ T500 shows potential to provide substantial and prolonged control of malaria transmitted by pyrethroid-resistant mosquito vectors when applied for IRS. Its addition to the current list of WHO-approved IRS insecticides will provide a suitable option to facilitate rotation of IRS products with different modes of action

Dry season refugia for anopheline larvae and mapping of the seasonal distribution in mosquito larval habitats in Kandi, northeastern Benin

BACKGROUND: The dynamics of mosquito populations depends on availability of suitable surface water for oviposition. It is well known that suitable management of mosquito larval habitats in the sub-Saharan countries, particularly during droughts, could help to suppress vector densities and malaria transmission. We conducted a field survey to investigate the spatial and seasonal distribution of mosquito larval habitats and identify drought-refugia for anopheline larvae. METHODS: A GIS approach was used to identify, geo-reference and follow up longitudinally from May 2012 to May 2013, all mosquito breeding sites in two rural sites (Yondarou and Thui), one urban (Kossarou), and one peri-urban (Pèdè) site at Kandi, a municipality in northeastern Benin. In Kandi, droughts are excessive with no rain for nearly six months and a lot of sunshine. A comprehensive record of mosquito larval habitats was conducted periodically in all sites for the identification of drought-refugia of anopheline larval stages. With geospatialisation data, seasonal larval distribution maps were generated for each study site with the software ArcGIS version 10.2. RESULTS: Overall, 187 mosquito breeding sites were identified of which 29.95% were recorded during drought. In rural, peri-urban and urban sites, most of the drought-refugia of anopheline larvae were domestic in nature (61.54%). Moreover, in rural settings, anopheline larvae were also sampled in cisterns and wells (25% of larval habitats sampled during drought in Yondarou and 20% in Thui). The mapping showed a significant decrease in the spatial distribution of mosquito larval habitats in rural, peri-urban and urban sites during drought, except in Yondarou (rural) where the aridity did not seem to influence the distribution of larval habitats. CONCLUSION: Our data showed that the main drought-refugia of anopheline larvae were of a domestic nature as well as wells and cisterns. A suitable management of mosquito larvae in sub-Saharan countries, particularly during droughts, should target such larval habitats for a meaningful impact on the dynamics of mosquito populations and malaria transmission