Annual Entomological Inoculation Rate Research Articles

Spatial–temporal vector abundance and malaria transmission dynamics in Nchelenge and Lake Mweru islands, a region with a high burden of malaria in northern Zambia

BackgroundOver a decade of vector control by indoor residual spraying (IRS) and long-lasting insecticidal nets (LLINs) distribution on the mainland, and only LLINs on islands had a minimal impact on disease burden in Nchelenge district, northern Zambia. Anopheles funestus and Anopheles gambiae are vectors known only from the mainland. Understanding vector bionomics in the district is necessary for planning and targeting effective vector control. This study aimed to provide information on abundance, seasonality, and Plasmodium falciparum sporozoite infectivity of malaria vectors in Nchelenge, including islands.MethodsMosquitoes were collected in 192 CDC indoor light traps set in 56 households between January 2015 and January 2016. Morphological and molecular species identifications and P. falciparum circumsporoites by ELISA were performed. Mosquito counts and relative abundances from the islands and mainland were compared, and household factors associated with vector counts were determined.ResultsA total of 5888 anophelines were collected during the study. Of these, 5,704 were female Anopheles funestus sensu lato (s.l.) and 248 female An. gambiae s.l. The highest proportion of An. funestus (n = 4090) was from Chisenga Island and An. gambiae (n = 174) was from Kilwa Island. The highest estimated counts per trap for An. funestus s.l. were from Chisenga island, (89.9, p < 0.001) and from the dry season (78.6, p < 001). For An. gambiae the highest counts per trap were from Kilwa island (3.1, p < 0.001) and the rainy season (2.5, p = 0.007). The highest estimated annual entomological inoculation rate was from Chisenga Island with 91.62 ib/p/y followed by Kilwa Island with 29.77 ib/p/yr, and then Mainland with 19.97 ib/p/yr.ConclusionsThere was varied species abundance and malaria transmission risk across sites and seasons. The risk of malaria transmission was perennial and higher on the islands. The minimal impact of vector control efforts on the mainland was evident, but limited overall. Vector control intervention coverage with effective tools needs to be extended to the islands to effectively control malaria transmission in Nchelenge district.

Estimating malaria transmission risk through surveillance of human–vector interactions in northern Ghana

BackgroundVector bionomics are important aspects of vector-borne disease control programs. Mosquito-biting risks are affected by environmental, mosquito behavior and human factors, which are important for assessing exposure risk and intervention impacts. This study estimated malaria transmission risk based on vector–human interactions in northern Ghana, where indoor residual spraying (IRS) and insecticide-treated nets (ITNs) have been deployed.MethodsIndoor and outdoor human biting rates (HBRs) were measured using monthly human landing catches (HLCs) from June 2017 to April 2019. Mosquitoes collected were identified to species level, and Anopheles gambiae sensu lato (An. gambiae s.l.) samples were examined for parity and infectivity. The HBRs were adjusted using mosquito parity and human behavioral observations.ResultsAnopheles gambiae was the main vector species in the IRS (81%) and control (83%) communities. Indoor and outdoor HBRs were similar in both the IRS intervention (10.6 vs. 11.3 bites per person per night [b/p/n]; z = −0.33, P = 0.745) and control communities (18.8 vs. 16.4 b/p/n; z = 1.57, P = 0.115). The mean proportion of parous An. gambiae s.l. was lower in IRS communities (44.6%) than in control communities (71.7%). After adjusting for human behavior observations and parity, the combined effect of IRS and ITN utilization (IRS: 37.8%; control: 57.3%) on reducing malaria transmission risk was 58% in IRS + ITN communities and 27% in control communities with ITNs alone (z = −4.07, P < 0.001). However, this also revealed that about 41% and 31% of outdoor adjusted bites in IRS and control communities respectively, occurred before bed time (10:00 pm). The mean directly measured annual entomologic inoculation rates (EIRs) during the study were 6.1 infective bites per person per year (ib/p/yr) for IRS communities and 16.3 ib/p/yr for control communities. After considering vector survival and observed human behavior, the estimated EIR for IRS communities was 1.8 ib/p/yr, which represents about a 70% overestimation of risk compared to the directly measured EIR; for control communities, it was 13.6 ib/p/yr (16% overestimation).ConclusionIndoor residual spraying significantly impacted entomological indicators of malaria transmission. The results of this study indicate that vector bionomics alone do not provide an accurate assessment of malaria transmission exposure risk. By accounting for human behavior parameters, we found that high coverage of ITNs alone had less impact on malaria transmission indices than combining ITNs with IRS, likely due to observed low net use. Reinforcing effective communication for behavioral change in net use and IRS could further reduce malaria transmission.Graphical

Entomological parameters and population structure at a microgeographic scale of the main Colombian malaria vectors Anopheles albimanus and Anopheles nuneztovari.

Population subdivision among several neotropical malaria vectors has been widely evaluated; however, few studies have analyzed population variation at a microgeographic scale, wherein local environmental variables may lead to population differentiation. The aim of the present study was to evaluate the genetic and geometric morphometric structure of Anopheles nuneztovari and Anopheles albimanus in endemic localities of northwestern Colombia. Genetic and phenetic structures were evaluated using microsatellites markers and wing geometric morphometrics, respectively. In addition, entomological indices of importance in transmission were calculated. Results showed that the main biting peaks of Anopheles nuneztovari were between 20:00 and 22:00, whereas Anopheles albimanus exhibited more variation in biting times among localities. Infection in An. nuneztovari by Plasmodium spp. (IR: 4.35%) and the annual entomological inoculation rate (30.31), indicated high vector exposure and local transmission risk. We did not detect Plasmodium-infected An. albimanus in this study. In general, low genetic and phenetic subdivision among the populations of both vectors was detected using a combination of phenotypic, genetic and environmental data. The results indicated high regional gene flow, although local environmental characteristics may be influencing the wing conformation differentiation and behavioral variation observed in An. albimanus. Furthermore, the population subdivision detected by microsatellite markers for both species by Bayesian genetic analysis provides a more accurate picture of the current genetic structure in comparison to previous studies. Finally, the biting behavior variation observed for both vectors among localities suggests the need for continuous malaria vector surveys covering the endemic region to implement the most effective integrated local control interventions.

Measures of malaria transmission, infection, and disease in an area bordering two districts with and without sustained indoor residual spraying of insecticide in Uganda.

Tororo District, in Eastern Uganda, experienced a dramatic decline in malaria burden starting in 2014 following the implementation of indoor residual spraying of insecticide (IRS) in the setting of repeated long-lasting insecticide treated nets (LLINs) distribution campaigns. However, in 2020 malaria began to resurge in Tororo following a change in the active ingredient used for IRS. In this study, epidemiological measures of malaria were compared shortly after the resurgence between two parishes in Tororo District (Kayoro and Osukuru) and one contiguous parish in Busia District (Buteba), where IRS has never been implemented. A cohort of 483 residents from 80 randomly selected households were followed from August 2020 to January 2021. Mosquitoes were collected every 2 weeks using CDC light traps in rooms where participants slept; parasitemia and gametoctyemia measured every 4 weeks by microscopy and PCR; and symptomatic malaria measured by passive surveillance. The annual entomological inoculation rate was significantly higher in Buteba (108.2 infective bites/person/year), compared to Osukuru (59.0, p = 0.001) and Kayoro (27.4, p<0.001). Overall, parasite prevalence was 19.5% by microscopy and 50.7% by PCR, with no significant differences between the three parishes. Among infected individuals, gametocyte prevalence by PCR was 45.5% and similar between sites. The incidence of malaria was significantly higher in Osukuru (2.46 episodes PPY) compared to Buteba (1.47, p = 0.005) and Kayoro (1.09, p<0.001). For participants over 15 years of age, the risk of symptomatic malaria if microscopic parasitemia was present was higher in Osukuru (relative risk [RR] = 2.99, p = 0.03) compared to Buteba. These findings highlight the complex relationships between measures of malaria transmission, infection, and disease, and the potential for excess disease burden, possibly due to waning immunity, in areas where vector control interventions begin to fail after a sustained period of highly effective control.

A prospective cohort study of Plasmodium falciparum malaria in three sites of Western Kenya

BackgroundMalaria in western Kenya is currently characterized by sustained high Plasmodial transmission and infection resurgence, despite positive responses in some areas following intensified malaria control interventions since 2006. This study aimed to evaluate long-term changes in malaria transmission profiles and to assess patterns of asymptomatic malaria infections in school children aged 5–15 years at three sites in western Kenya with heterogeneous malaria transmission and simultaneous malaria control interventions.MethodsThe study was conducted from 2018 to 2019 and is based on data taken every third year from 2005 to 2014 during a longitudinal parasitological and mosquito adult surveillance and malaria control programme that was initiated in 2002 in the villages of Kombewa, Iguhu, and Marani. Plasmodium spp. infections were determined using microscopy. Mosquito samples were identified to species and host blood meal source and sporozoite infections were assayed using polymerase chain reaction.ResultsPlasmodium falciparum was the only malaria parasite evaluated during this study (2018–2019). Asymptomatic malaria parasite prevalence in school children decreased in all sites from 2005 to 2008. However, since 2011, parasite prevalence has resurged by > 40% in Kombewa and Marani. Malaria vector densities showed similar reductions from 2005 to 2008 in all sites, rose steadily until 2014, and decreased again. Overall, Kombewa had a higher risk of infection compared to Iguhu (χ2 = 552.52, df = 1, P < 0.0001) and Marani (χ2 = 1127.99, df = 1, P < 0.0001). There was a significant difference in probability of non-infection during malaria episodes (log-rank test, χ2 = 617.59, df = 2, P < 0.0001) in the study sites, with Kombewa having the least median time of non-infection during malaria episodes. Gender bias toward males in infection was observed (χ2 = 27.17, df = 1, P < 0.0001). The annual entomological inoculation rates were 5.12, 3.65, and 0.50 infective bites/person/year at Kombewa, Iguhu, and Marani, respectively, during 2018 to 2019.ConclusionsMalaria prevalence in western Kenya remains high and has resurged in some sites despite continuous intervention efforts. Targeting malaria interventions to those with asymptomatic infections who serve as human reservoirs might decrease malaria transmission and prevent resurgences. Longitudinal monitoring enables detection of changes in parasitological and entomological profiles and provides core baseline data for the evaluation of vector interventions and guidance for future planning of malaria control.Graphical abstract

Assessment of malaria transmission intensity and insecticide resistance mechanisms in three rural areas of the Moyen Ogooué Province of Gabon

BackgroundVector control is considered to be the most successful component of malaria prevention programs and a major contributor to the reduction of malaria incidence over the last two decades. However, the success of this strategy is threatened by the development of resistance to insecticides and behavioural adaptations of vectors. The aim of this study was to monitor malaria transmission and the distribution of insecticide resistance genes in Anopheles populations from three rural areas of the Moyen Ogooué Province of Gabon.MethodsAnopheles spp. were collected using human landing catches in Bindo, Nombakélé and Zilé, three villages located in the surroundings of Lambaréné, during both the rainy and dry seasons. Mosquitoes were identified morphologically, and DNA was extracted from heads and thoraces. Members of the Anopheles gambiae complex were identified by molecular methods using the PCR SINE200 protocol and by sequencing of the internal transcribed spacer 2 region. Taqman assays were used to determine Plasmodium infection and the presence of resistance alleles.ResultsAnopheles gambiae sensu lato (97.7%), An. moucheti (1.7%) and An. coustani (0.6%) were the three groups of species collected. Anopheles gambiae sensu stricto (98.5%) and An. coluzzii (1.5%) were the only species of the An. gambiae complex present in the collection. Of the 1235 Anopheles collected, 1193 were collected during the rainy season; these exhibited an exophagic behaviour, and consistently more mosquitoes were collected outdoor than indoor in the three study areas. Of the 1166 Anopheles screened, 26 (2.2%) were infected with Plasmodium species, specifically Plasmodium falciparum (66.7%), P. malariae (15.4%), P. ovale curtisi (11.5%) and P. ovale wallikeri (3.8%). Malaria transmission intensity was high in Zilé, with an average annual entomological inoculation rate (aEIR) of 243 infective bites per year, while aEIRs in Bindo and Nombakélé were 80.2 and 17 infective bites per year, respectively. Both the L1014F and L1014S mutations were present at frequencies > 95% but no Ace1G119S mutation was found.ConclusionOur results demonstrate that malaria transmission intensity is heterogeneous in these three rural areas of Moyen Ogooué Province, with areas of high transmission, such as Zilé. The exophagic behaviour of the mosquitoes as well as the high frequency of resistance mutations are serious challenges that need to be addressed by the deployment of control measures adapted to the local setting.Graphical

High vectorial transmission of malaria in urban and rural settings in the northern, western and eastern regions of Côte d'Ivoire.

Malaria remains a public health problem in Côte d'Ivoire. To cope with this issue, the Ministry of Health established strategies through Long-Lasting Insecticidal Nets (LLINs) and artemisinin-based medicines. To better understand the influence of periodic mass distribution of LLINs on malaria transmission, this entomological survey was conducted in three regions of Côte d'Ivoire. Mosquitoes were sampled by Human Landing Catches (HLC) in urban and rural settings of Korhogo, Man and Abengourou. Mosquitoes were identified morphologically and by molecular methods. Plasmodium falciparum infection was assessed by ELISA, and the Entomological Inoculation Rates (EIR) were calculated for each species and setting. Only An. gambiae s.l. was identified in Korhogo and in Abengourou while An. gambiae s.l. and An. funestus s.l. was reported in Man. An. coluzzii was the most abundant species of the An. gambiae siblings collected in Abengourou, and in Man while An. gambiae was most abundant in Korhogo. In urban settings, malaria vectors showed high aggressiveness (>11 bites per person per night) and the annual EIR was high (83.22-438.44 infectious bites per person per year). In rural settings, malaria vectors showed also high aggressiveness (19-52 b/p/n). The annual EIR is very high (>94 ib/p/yr). However, the weakest EIR was recorded in the northern region with 94.90 ib/p/yr. This work indicates that malaria transmission remains high and heterogeneous across Côte d'Ivoire, despite repeated mass distribution of LLINs. Also, in Man, malaria transmission is more intense with the involvement of two main vectors. Furthermore, in the village of Korhogo, the EIR remained relatively low.

Partial indoor residual spraying with pirimiphos-methyl as an effective and cost-saving measure for the control of Anopheles gambiae s.l. in northern Ghana

The scale up of indoor residual spraying (IRS) and insecticide treated nets have contributed significantly to global reductions in malaria prevalence over the last two decades. However, widespread pyrethroid resistance has necessitated the use of new and more expensive insecticides for IRS. Partial IRS with pirimiphos-methyl in experimental huts and houses in a village-wide trial was evaluated against Anopheles gambiae s.l. in northern Ghana. Four different scenarios in which either only the top or bottom half of the walls of experimental huts were sprayed, with or without also spraying the ceiling were compared. Mortality of An. gambiae s.l. on partially sprayed walls was compared with the standard procedures in which all walls and ceiling surfaces are sprayed. A small-scale trial was then conducted to assess the effectiveness, feasibility, and cost of spraying only the upper walls and ceiling as compared to full IRS and no spraying in northern Ghana. Human landing catches were conducted to estimate entomological indices and determine the effectiveness of partial IRS. An established transmission dynamics model was parameterized by an analysis of the experimental hut data and used to predict the epidemiological impact and cost effectiveness of partial IRS for malaria control in northern Ghana. In the experimental huts, partial IRS of the top (IRR 0.89, p = 0.13) or bottom (IRR 0.90, p = 0.15) half of walls and the ceiling was not significantly less effective than full IRS in terms of mosquito mortality. In the village trial, the annual entomological inoculation rate was higher for the unsprayed control (217 infective bites/person/year (ib/p/yr)) compared with the fully and partially sprayed sites, with 28 and 38 ib/p/yr, respectively. The transmission model predicts that the efficacy of partial IRS against all-age prevalence of malaria after six months would be broadly equivalent to a full IRS campaign in which 40% reduction is expected relative to no spray campaign. At scale, partial IRS in northern Ghana would have resulted in a 33% cost savings ($496,426) that would enable spraying of 36,000 additional rooms. These findings suggest that partial IRS is an effective, feasible, and cost saving approach to IRS that could be adopted to sustain and expand implementation of this key malaria control intervention.

Diversity of Anopheles Gambiae s.l., Giles (Diptera: Culicidae) Larval Habitats in Urban Areas and Malaria Transmission in Bouaké, Côte d'Ivoire.

Malaria vectors are supposedly uncommon in urban areas owing to the lack of suitable breeding sites for their development. However, the maintenance in urban areas of traditional rural practices along with humanitarian crisis can create favorable conditions for malaria transmission. This study aimed to provide relevant entomological data on the risk of malaria transmission in the city of Bouaké, after the military-political crisis from 2002 to 2011 in Côte d'Ivoire. Adults mosquitoes were collected by human landing catches in Dar Es Salam, Kennedy and N'gattakro neighborhoods. Potential breeding sites were georeferenced and mapped using a GPS. Mosquito species were identified morphologically and by molecular methods. Plasmodium infections were detected by quantitative PCR. Anopheline larvae were found in rice and vegetable crops, puddles, and footprints. A total of 939 Anopheles gambiae s.l. were caught during the surveys. The average human biting rate was 8.8 bites/person/night. The A. gambiae s.l. species were A. gambiae s.s (89.6%) and Anopheles coluzzii (10.4%). The average infectivity rate was 0.74% and the average annual entomological inoculation rate was estimated at 19 infected bites/person/year ranging from 0 in Dar Es Salam and N'gattakro to 58 in Kennedy. The risk of malaria transmission exists in Bouaké city, although Plasmodium infections are low.

Within\u2010household clustering of genetically related Plasmodium falciparum infections in a moderate transmission area of Uganda

BackgroundEvaluation of genetic relatedness of malaria parasites is a useful tool for understanding transmission patterns, but patterns are not easily detectable in areas with moderate to high malaria transmission. To evaluate the feasibility of detecting genetic relatedness in a moderate malaria transmission setting, relatedness of Plasmodium falciparum infections was measured in cohort participants from randomly selected households in the Kihihi sub-county of Uganda (annual entomological inoculation rate of 27 infectious bites per person).MethodsAll infections detected via microscopy or Plasmodium-specific loop mediated isothermal amplification from passive and active case detection during August 2011-March 2012 were genotyped at 26 microsatellite loci, providing data for 349 samples from 230 participants living in 80 households. Pairwise genetic relatedness was calculated using identity by state (IBS).ResultsAs expected, genetic diversity was high (mean heterozygosity [He] = 0.73), and the majority (76.5 %) of samples were polyclonal. Despite the high genetic diversity, fine-scale population structure was detectable, with significant spatiotemporal clustering of highly related infections. Although the difference in malaria incidence between households at higher (mean 1127 metres) versus lower elevation (mean 1015 metres) was modest (1.4 malaria cases per person-year vs. 1.9 per person-year, respectively), there was a significant difference in multiplicity of infection (2.2 vs. 2.6, p = 0.008) and, more strikingly, a higher proportion of highly related infections within households (6.3 % vs. 0.9 %, p = 0.0005) at higher elevation compared to lower elevation.ConclusionsGenetic data from a relatively small number of diverse, multiallelic loci reflected fine scale patterns of malaria transmission. Given the increasing interest in applying genetic data to augment malaria surveillance, this study provides evidence that genetic data can be used to inform transmission patterns at local spatial scales even in moderate transmission areas.

Malaria Transmission, Infection, and Disease following Sustained Indoor Residual Spraying of Insecticide in Tororo, Uganda.

Tororo, a district in Uganda with historically high malaria transmission intensity, has recently scaled up control interventions, including universal long-lasting insecticidal net distribution in 2013 and 2017, and sustained indoor residual spraying (IRS) of insecticide since December 2014. We describe the burden of malaria in Tororo 5 years following the initiation of IRS. We followed a cohort of 531 participants from 80 randomly selected households in Nagongera subcounty, Tororo district, from October 2017 to October 2019. Mosquitoes were collected every 2 weeks using CDC light traps in all rooms where participants slept, symptomatic malaria was identified by passive surveillance, and microscopic and submicroscopic parasitemia were measured every 4 weeks using active surveillance. Over the 2 years of follow-up, 15,780 female anopheline mosquitos were collected, the majority (98.0%) of which were Anopheles arabiensis. The daily human biting rate was 2.07, and the annual entomological inoculation rate was 0.43 infective bites/person/year. Only 38 episodes of malaria were diagnosed (incidence 0.04 episodes/person/year), and there were no cases of severe malaria or malarial deaths. The prevalence of microscopic parasitemia was 1.9%, and the combined prevalence of microscopic and submicroscopic parasitemia was 10.4%, each highest in children aged 5-15 years (3.3% and 14.0%, respectively). After 5 years of intensive vector control measures in Tororo, the burden of malaria was reduced to very low transmission levels. However, a significant proportion of the population remained parasitemic, primarily school-aged children with submicroscopic parasitemia, providing a potential reservoir for malaria transmission.

Ecology and Contribution of Anopheles hancocki Edwards, 1929 in Malaria Transmission in a Village of South Cameroon Forest Block

Anopheles hancocki is one of the secondary vectors of malaria whose larval ecology in the South Cameroonian forest block is still unknown. This information is however fundamental for developing efficient and sustainable control strategies against this mosquito in localities where it acts as a disease vector. The present study describes the larval ecology of A. hancocki and its contribution in malaria transmission in a riverbank village of the Ayos Health District. Mosquito sampling took place in 2018 on a quarterly rate, combining the dipping method for larval collection with adult mosquito capture on volunteers. For each of the breeding sites, physicochemical characteristics were measured and larvae were collected and reared to adult. Molecular alongside morpho-taxonomic techniques were used for the identification of mosquito species. Physiological age was determined based on the appearance of their ovarian tracheoles and CSP Elisa test was used to assess infectivity. In total, 3,618 adult mosquitoes belonging to seven species were collected in the study area, namely A. hancocki, Anopheles gambiae, Anopheles moucheti, Mansonia africana, Culex pipiens quinquefasciatus, Aedes albopictus and Aedes aegypti. Breeding sites of A. hancocki were similar to those of A. gambiae. However, the total dissolved solids and conductivity values were significantly higher in A. gambiae breeding sites than in those of A. hancocki. A. hancocki was the most aggressive mosquito species and represented 45.6% of the local aggressive culicidofauna. Male species' nocturnal cycle of aggression showed maximum activity between 8 pm and 10 pm. Females of this species were significantly older than those of A. gambiae and contributed to 40% of malaria transmission in the locality with an average annual Entomological Inoculation Rate (EIR) of 2.92 ib/p/year lower than that of A. gambiae (3.65 ib/p/year). Except few differences, ecological requirements for the development of A. hancocki larvae are similar to that of A. gambiae. A. hancocki contributes to the perennial transmission of malaria in the Ayos area; implementation of vector control strategies is therefore needed.

Impact of vector control interventions on malaria transmission intensity, outdoor vector biting rates and Anopheles mosquito species composition in Tororo, Uganda

BackgroundLong-lasting insecticidal nets (LLINs) and indoor residual spraying of insecticide (IRS) are widely recommended for the prevention of malaria in endemic regions. Data from human landing catches provide information on the impact of vector control on vector populations. Here, malaria transmission indoors and outdoors, before and after mass deployment of LLINs and IRS in Uganda was compared.MethodsThe study took place in Tororo district, a historically high transmission area where universal LLIN distribution was conducted in November 2013 and May 2017 and 6 rounds of IRS implemented from December 2014 to July 2018. Human landing catches were performed in 8 houses monthly from October 2011 to September 2012 (pre-intervention period) and every 4 weeks from November 2017 to October 2018 (post-intervention period). Mosquitoes were collected outdoors from 18:00 to 22:00 h and indoors from 18:00 to 06:00 h. Female Anopheles were tested for the presence of Plasmodium falciparum sporozoites and species identification performed using gross dissection and polymerase chain reaction (PCR).ResultsThe interventions were associated with a decline in human biting rate from 19.6 to 2.3 female Anopheles mosquitoes per house per night (p < 0.001) and annual entomological inoculation rate from 129 to 0 infective bites per person per year (p < 0.001). The proportion of mosquitoes collected outdoors increased from 11.6 to 49.4% (p < 0.001). Prior to the interventions the predominant species was Anopheles gambiae sensu stricto (s.s.), which comprised an estimated 76.7% of mosquitoes. Following the interventions, the predominant species was Anopheles arabiensis, which comprised 99.5% of mosquitoes, with almost complete elimination of An. gambiae s.s. (0.5%).ConclusionsMass distribution of LLINs and 6 rounds of IRS dramatically decreased vector density and sporozoite rate resulting in a marked reduction in malaria transmission intensity in a historically high transmission site in Uganda. These changes were accompanied by a shift in vector species from An. gambiae s.s. to An. arabiensis and a relative increase in outdoor biting.

Vectorial Transmission of Malaria in Major Districts of Côte d'Ivoire.

To better understand the influence of periodic mass distribution of Long-Lasting Insecticidal Nets (LLINs) on malaria transmission, a 1-yr entomological survey was conducted in three major districts of Côte d'Ivoire. Mosquitoes were sampled by Human Landing Catches (HLC) in urban and rural areas of San Pedro and Abidjan (coastal), and in Yamoussoukro (central). Mosquitoes were identified morphologically and by molecular methods. The Plasmodium falciparum circumsporozoite (CSP) indices were measured by ELISA, and the Entomological Inoculation Rates (EIR) were calculated for each species and area. Anopheles gambiae s.l. Giles (Diptera: Culicidae) and Anopheles nili Theobald (Diptera: Culicidae) were identified in coastal districts, while An. gambiae s.l. and Anopheles funestus Giles (Diptera: Culicidae) were reported in the central district. In urban areas, malaria vectors showed a low aggressiveness (<10 bites per person per night), except in Yamoussoukro, where up to 18.9 b/p/n were recorded. The annual EIR was higher in the central urban area (138.7 infected bites per person per year) than in coastal ones (10-62 ib/p/n). In rural areas, malaria vectors were highly aggressive with an average 13 b/p/n for An. gambiae s.l, 21.2 b/p/n for An. nili and 12 b/p/n for An. funestus. The annual EIR ranged between 94.9 and 193.4 infected bites per person per year. This work indicates that, despite repeated mass distribution of LLINs, malaria transmission remains high and heterogeneous across Côte d'Ivoire. Malaria transmission was lower in coastal urban areas than in the central one, and remains high rural areas where two additional Anopheles vectors are involved in malaria transmission.

Modelling reactive case detection strategies for interrupting transmission of Plasmodium falciparum malaria

BackgroundAs areas move closer to malaria elimination, a combination of limited resources and increasing heterogeneity in case distribution and transmission favour a shift to targeted reactive interventions. Reactive case detection (RCD), the following up of additional individuals surrounding an index case, has the potential to target transmission pockets and identify asymptomatic cases in them. Current RCD implementation strategies vary, and it is unclear which are most effective in achieving elimination.MethodsOpenMalaria, an established individual-based stochastic model, was used to simulate RCD in a Zambia-like setting. The capacity to follow up index cases, the search radius, the initial transmission and the case management coverage were varied. Suitable settings were identified and probabilities of elimination and time to elimination estimated. The value of routinely collected prevalence and incidence data for predicting the success of RCD was assessed.ResultsThe results indicate that RCD with the aim of transmission interruption is only appropriate in settings where initial transmission is very low (annual entomological inoculation rate (EIR) 1–2 or prevalence approx. < 7–19% depending on case management levels). Every index case needs to be followed up, up to a maximum case-incidence threshold which defines the suitability threshold of settings for elimination using RCD. Increasing the search radius around index cases is always beneficial.ConclusionsRCD is highly resource intensive, requiring testing and treating of 400–500 people every week for 5–10 years for a reasonable chance of elimination in a Zambia-like setting.

High malaria transmission sustained by Anopheles gambiae s.l. occurring both indoors and outdoors in the city of Yaoundé, Cameroon

Background: Malaria remains a major public health problem in Cameroon; however, despite reports on the adaptation of anopheline species to urban habitats, there is still not enough information on malaria transmission pattern in urban settings. In the frame of a larval control trial in the city of Yaoundé, we conducted baseline surveys to assess malaria transmission dynamics in this city. Methods: Adult mosquitoes were collected indoors and outdoors using CDC light traps and human landing catches from March 2017 to March 2018 in 30 districts of Yaoundé, Cameroon. Mosquitoes were sorted by genus and identified to the species level using PCR. The TaqMan method and ELISA were used to determine mosquito infection status to Plasmodium. Bioassays were conducted to assess female Anopheles gambiae susceptibility to insecticides. Results: A total of 218,991 mosquitoes were collected. The main malaria vectors were An. gambiae s.l. (n=6154) and An. funestus s.l. (n=229). Of the 1476 An. gambiae s.l. processed by PCR, 92.19% were An. coluzzii and 7.81% An. gambiae. An. funestus s.l. was composed of 93.01% (173/186) An. funestus and 4.84% (13/186) An. leesoni. The average biting rate of anopheline was significantly high outdoor than indoor (P=0.013). Seasonal variation in mosquito abundance and biting rate was recorded. The infection rate by Plasmodium falciparum was 2.13% (104/4893 mosquitoes processed). The annual entomological inoculation rate was found to vary from 0 to 92 infective bites/man/year (ib/m/y). Malaria transmission risk was high outdoor (66.65 ib/m/y) compared to indoor (31.14 ib/m/y). An. gambiae s.l. was found highly resistant to DDT, permethrin and deltamethrin. High prevalence of the West Africa kdr allele 1014F was recorded and this was not found to influence An. gambiae s.l. infection status. Conclusion: The study suggests high malaria transmission occurring in the city of Yaoundé and call for immediate actions to improve control strategies.

High malaria transmission sustained by Anopheles gambiae s.l. occurring both indoors and outdoors in the city of Yaoundé, Cameroon.

Background: Malaria remains a major public health problem in Cameroon; however, despite reports on the adaptation of anopheline species to urban habitats, there is still not enough information on malaria transmission pattern in urban settings. In the frame of a larval control trial in the city of Yaoundé, we conducted baseline surveys to assess malaria transmission dynamics in this city. Methods: Adult mosquitoes were collected indoors and outdoors using CDC light traps and human landing catches from March 2017 to March 2018 in 30 districts of Yaoundé, Cameroon. Mosquitoes were sorted by genus and identified to the species level using PCR. The TaqMan method and ELISA were used to determine mosquito infection status to Plasmodium. Bioassays were conducted to assess female Anopheles gambiae susceptibility to insecticides. Results: A total of 218,991 mosquitoes were collected. The main malaria vectors were An. gambiae s.l. (n=6154) and An. funestus s.l. (n=229). Of the 1476 An. gambiae s.l. processed by PCR, 92.19% were An. coluzzii and 7.81% An. gambiae. An. funestus s.l. was composed of 93.01% (173/186) An. funestus and 4.84% (13/186) An. leesoni. The average biting rate of anopheline was significantly high outdoor than indoor (P=0.013). Seasonal variation in mosquito abundance and biting rate was recorded. The infection rate by Plasmodium falciparum was 2.13% (104/4893 mosquitoes processed). The annual entomological inoculation rate was found to vary from 0 to 92 infective bites/man/year (ib/m/y). Malaria transmission risk was high outdoor (66.65 ib/m/y) compared to indoor (31.14 ib/m/y). An. gambiae s.l. was found highly resistant to DDT, permethrin and deltamethrin. High prevalence of the West Africa kdr allele 1014F was recorded and this was not found to influence An. gambiae s.l. infection status. Conclusion: The study suggests high malaria transmission occurring in the city of Yaoundé and call for immediate actions to improve control strategies.

Assessment of community-level effects of intermittent preventive treatment for malaria in schoolchildren in Jinja, Uganda (START-IPT trial): a cluster-randomised trial

SummaryBackgroundIntermittent preventive treatment (IPT) is a well established malaria control intervention. Evidence that delivering IPT to schoolchildren could provide community-level benefits is limited. We did a cluster-randomised controlled trial to assess the effect of IPT of primary schoolchildren with dihydroartemisinin-piperaquine (DP) on indicators of malaria transmission in the community, in Jinja, Uganda.MethodsWe included 84 clusters, each comprising one primary school and the 100 closest available households. The clusters were randomly assigned 1:1 to receive IPT with DP or standard care (control) by restricted randomisation to ensure balance by geography and school type. Children in intervention schools received IPT monthly for up to six rounds (June to December, 2014). We did cross-sectional community surveys in randomly selected households at baseline and in January to April, 2015, during which we measured participants' temperatures and obtained finger-prick blood smears for measurement of parasite prevalence by microscopy. We also did entomological surveys 1 night per month in households from 20 randomly selected IPT and 20 control clusters. The primary trial outcome was parasite prevalence in the final community survey. The primary entomological survey outcome was the annual entomological inoculation rate (aEIR) from July, 2014, to April, 2015. This trial is registered at ClinicalTrials.gov, number NCT02009215.FindingsAmong 23 280 students registered in the 42 intervention schools, 10 079 (43%) aged 5–20 years were enrolled and received at least one dose of DP. 9286 (92%) of 10 079 received at least one full course of DP (three doses). Community-level parasite prevalence was lower in the intervention clusters than in the control clusters (19% vs 23%, adjusted risk ratio 0·85, 95% CI 0·73–1·00, p=0·05). The aEIR was lower in the intervention group than in the control group, but not significantly so (10·1 vs 15·2 infective bites per person, adjusted incidence rate ratio 0·80, 95% CI 0·36–1·80, p=0·59).InterpretationIPT of schoolchildren with DP might have a positive effect on community-level malaria indicators and be operationally feasible. Studies with greater IPT coverage are needed.FundingUK Medical Research Council, UK Department for International Development, and Wellcome Trust.

Is outdoor vector control needed for malaria elimination? An individual-based modelling study

BackgroundResidual malaria transmission has been reported in many areas even with adequate indoor vector control coverage, such as long-lasting insecticidal nets (LLINs). The increased insecticide resistance in Anopheles mosquitoes has resulted in reduced efficacy of the widely used indoor tools and has been linked with an increase in outdoor malaria transmission. There are considerations of incorporating outdoor interventions into integrated vector management (IVM) to achieve malaria elimination; however, more information on the combination of tools for effective control is needed to determine their utilization.MethodsA spatial individual-based model was modified to simulate the environment and malaria transmission activities in a hypothetical, isolated African village setting. LLINs and outdoor attractive toxic sugar bait (ATSB) stations were used as examples of indoor and outdoor interventions, respectively. Different interventions and lengths of efficacy periods were tested. Simulations continued for 420 days, and each simulation scenario was repeated 50 times. Mosquito populations, entomologic inoculation rates (EIRs), probabilities of local mosquito extinction, and proportion of time when the annual EIR was reduced below one were compared between different intervention types and efficacy periods.ResultsIn the village setting with clustered houses, the combinational intervention of 50% LLINs plus outdoor ATSBs significantly reduced mosquito population and EIR in short term, increased the probability of local mosquito extinction, and increased the time when annual EIR is less than one per person compared to 50% LLINs alone; outdoor ATSBs alone significantly reduced mosquito population in short term, increased the probability of mosquito extinction, and increased the time when annual EIR is less than one compared to 50% LLINs alone, but there was no significant difference in EIR in short term between 50% LLINs and outdoor ATSBs. In the village setting with dispersed houses, the combinational intervention of 50% LLINs plus outdoor ATSBs significantly reduced mosquito population in short term, increased the probability of mosquito extinction, and increased the time when annual EIR is less than one per person compared to 50% LLINs alone; outdoor ATSBs alone significantly reduced mosquito population in short term, but there were no significant difference in the probability of mosquito extinction and the time when annual EIR is less than one between 50% LLIN and outdoor ATSBs; and there was no significant difference in EIR between all three interventions. A minimum of 2 months of efficacy period is needed to bring out the best possible effect of the vector control tools, and to achieve long-term mosquito reduction, a minimum of 3 months of efficacy period is needed.ConclusionsThe results highlight the value of incorporating outdoor vector control into IVM as a supplement to traditional indoor practices for malaria elimination in Africa, especially in village settings of clustered houses where LLINs alone is far from sufficient.

Interventions that effectively target Anopheles funestus mosquitoes could significantly improve control of persistent malaria transmission in south-eastern Tanzania.

Malaria is transmitted by many Anopheles species whose proportionate contributions vary across settings. We re-assessed the roles of Anopheles arabiensis and Anopheles funestus, and examined potential benefits of species-specific interventions in an area in south-eastern Tanzania, where malaria transmission persists, four years after mass distribution of long-lasting insecticide-treated nets (LLINs). Monthly mosquito sampling was done in randomly selected households in three villages using CDC light traps and back-pack aspirators, between January-2015 and January-2016, four years after the last mass distribution of LLINs in 2011. Multiplex polymerase chain reaction (PCR) was used to identify members of An. funestus and Anopheles gambiae complexes. Enzyme-linked immunosorbent assay (ELISA) was used to detect Plasmodium sporozoites in mosquito salivary glands, and to identify sources of mosquito blood meals. WHO susceptibility assays were done on wild caught female An. funestus s.l, and physiological ages approximated by examining mosquito ovaries for parity. A total of 20,135 An. arabiensis and 4,759 An. funestus were collected. The An. funestus group consisted of 76.6% An. funestus s.s, 2.9% An. rivulorum, 7.1% An. leesoni, and 13.4% unamplified samples. Of all mosquitoes positive for Plasmodium, 82.6% were An. funestus s.s, 14.0% were An. arabiensis and 3.4% were An. rivulorum. An. funestus and An. arabiensis contributed 86.21% and 13.79% respectively, of annual entomological inoculation rate (EIR). An. arabiensis fed on humans (73.4%), cattle (22.0%), dogs (3.1%) and chicken (1.5%), but An. funestus fed exclusively on humans. The An. funestus populations were 100% susceptible to organophosphates, pirimiphos methyl and malathion, but resistant to permethrin (10.5% mortality), deltamethrin (18.7%), lambda-cyhalothrin (18.7%) and DDT (26.2%), and had reduced susceptibility to bendiocarb (95%) and propoxur (90.1%). Parity rate was higher in An. funestus (65.8%) than An. arabiensis (44.1%). Though An. arabiensis is still the most abundant vector species here, the remaining malaria transmission is predominantly mediated by An. funestus, possibly due to high insecticide resistance and high survival probabilities. Interventions that effectively target An. funestus mosquitoes could therefore significantly improve control of persistent malaria transmission in south–eastern Tanzania.