Anopheles mosquito surveillance in Madagascar reveals multiple blood feeding behavior and Plasmodium infection

Tedrow, Riley E.; Rakotomanga, Tovonahary Angelo; Nepomichene, Thiery Nirina Jean Jose; Howes, Rosalind E.; Ratovonjato, Jocelyn; Ratsimbasoa, Arsène; Svenson, Gavin J.; Zimmerman, Peter A.

doi:10.1371/journal.pntd.0007176

Cited by 34 publications

(42 citation statements)

References 60 publications

(81 reference statements)

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“…In the Tsiroanomandidy district which constitutes a bridge area between the low transmission Central Highlands and the high endemic western region, both P. falciparum and P. vivax circulate. In this area, malaria prevalence and Anopheles species distribution have been described in detail [7,12,13]. Such combined parasitological and entomological information is critical for developing effective strategies for interrupting malaria transmission and moving towards malaria elimination which has been set up on the agenda of the 2018-2022 Malagasy Malaria Strategic Plan as geographically progressive elimination.…”

Section: Introductionmentioning

confidence: 99%

Differential contribution of Anopheles coustani and Anopheles arabiensis to the transmission of Plasmodium falciparum and Plasmodium vivax in two neighbouring villages of Madagascar

et al. 2020

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Background: Malaria is still a heavy public health concern in Madagascar. Few studies combining parasitology and entomology have been conducted despite the need for accurate information to design effective vector control measures. In a Malagasy region of moderate to intense transmission of both Plasmodium falciparum and P. vivax, parasitology and entomology have been combined to survey malaria transmission in two nearby villages. Methods: Community-based surveys were conducted in the villages of Ambohitromby and Miarinarivo at three time points (T1, T2 and T3) during a single malaria transmission season. Human malaria prevalence was determined by rapid diagnostic tests (RDTs), microscopy and real-time PCR. Mosquitoes were collected by human landing catches and pyrethrum spray catches and the presence of Plasmodium sporozoites was assessed by TaqMan assay. Results: Malaria prevalence was not significantly different between villages, with an average of 8.0% by RDT, 4.8% by microscopy and 11.9% by PCR. This was mainly due to P. falciparum and to a lesser extent to P. vivax. However, there was a significantly higher prevalence rate as determined by PCR at T2 (χ 2 2 = 7.46, P = 0.025). Likewise, mosquitoes were significantly more abundant at T2 (χ 2 2 = 64.8, P < 0.001), especially in Ambohitromby. At T1 and T3 mosquito abundance was higher in Miarinarivo than in Ambohitromby (χ 2 2 = 14.92, P < 0.001). Of 1550 Anopheles mosquitoes tested, 28 (1.8%) were found carrying Plasmodium sporozoites. The entomological inoculation rate revealed that Anopheles coustani played a major contribution in malaria transmission in Miarinarivo, being responsible of 61.2

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Section: Introductionmentioning

confidence: 99%

Differential contribution of Anopheles coustani and Anopheles arabiensis to the transmission of Plasmodium falciparum and Plasmodium vivax in two neighbouring villages of Madagascar

et al. 2020

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“…Changes in vector species composition and behaviour driven by large-scale coverage of vector control interventions (such as the 2013 and 2015 national campaigns to distribute insecticide-treated nets) could potentially also result in shifts to the timings of the transmission season [39]. For example, a novel vector, Anopheles coustani, was recently described in the Malagasy highlands [40], and evidence of strong, fine-spatial scale differences in vector behaviour also allows for adaptive plasticity in response to external pressures which could translate to changes in parasite transmission over time [41]. Given this reality, future iterations of this work could use a moving window approach to continually update the model with new data.…”

Section: Discussionmentioning

confidence: 99%

Mapping malaria seasonality in Madagascar using health facility data

Nguyen

Howes

Lucas

et al. 2020

BMC Med

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Background: Many malaria-endemic areas experience seasonal fluctuations in case incidence as Anopheles mosquito and Plasmodium parasite life cycles respond to changing environmental conditions. Identifying location-specific seasonality characteristics is useful for planning interventions. While most existing maps of malaria seasonality use fixed thresholds of rainfall, temperature, and/or vegetation indices to identify suitable transmission months, we construct a statistical modelling framework for characterising the seasonal patterns derived directly from monthly health facility data. Methods: With data from 2669 of the 3247 health facilities in Madagascar, a spatiotemporal regression model was used to estimate seasonal patterns across the island. In the absence of catchment population estimates or the ability to aggregate to the district level, this focused on the monthly proportions of total annual cases by health facility level. The model was informed by dynamic environmental covariates known to directly influence seasonal malaria trends. To identify operationally relevant characteristics such as the transmission start months and associated uncertainty measures, an algorithm was developed and applied to model realisations. A seasonality index was used to incorporate burden information from household prevalence surveys and summarise 'how seasonal' locations are relative to their surroundings. Results: Positive associations were detected between monthly case proportions and temporally lagged covariates of rainfall and temperature suitability. Consistent with the existing literature, model estimates indicate that while most parts of Madagascar experience peaks in malaria transmission near March-April, the eastern coast experiences an earlier peak around February. Transmission was estimated to start in southeast districts before southwest districts, suggesting that indoor residual spraying should be completed in the same order. In regions where the data suggested conflicting seasonal signals or two transmission seasons, estimates of seasonal features had larger deviations and therefore less certainty. Conclusions: Monthly health facility data can be used to establish seasonal patterns in malaria burden and augment the information provided by household prevalence surveys. The proposed modelling framework allows for evidence-based and cohesive inferences on location-specific seasonal characteristics. As health surveillance systems continue to improve, it is hoped that more of such data will be available to improve our understanding and planning of intervention strategies.

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“…This species is more zoophilic and exophagic than An. coustani, although an unexpectedly high degree of anthropophily has been revealed in southern Zambia [61] and Madagascar [69], and Plasmodium infection has incriminated the species as a vector in both countries [61,69]. In Barotseland An.…”

Section: Discussionmentioning

confidence: 99%

Geographically extensive larval surveys reveal an unexpected scarcity of primary vector mosquitoes in a region of persistent malaria transmission in western Zambia

Cross¹,

Thomas

McKeown³

et al. 2020

Preprint

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Background: The Barotse floodplains of the upper Zambezi River and its tributaries are a highly dynamic environment, with seasonal flooding and transhumance presenting a shifting mosaic of potential larval habitat and human and livestock bloodmeals for malaria vector mosquitoes. However, limited entomological surveillance has been undertaken to characterise the vector community in these floodplains and their environs. Such information is necessary as, despite substantial deployment of insecticide-treated nets (ITNs) and indoor residual spraying (IRS) against Anopheles vectors, malaria transmission persists across Barotseland in Zambia’s Western Province.Methods: Geographically extensive larval surveys were undertaken in two health districts along 102 km of transects, at fine spatial resolution, during a dry season and following the peak of the successive wet season. Larvae were sampled within typical Anopheles flight range of human settlements and identified through genetic sequencing of cytochrome c oxidase I and internal transcribed spacer 2 regions of mitochondrial and nuclear DNA. This facilitated detailed comparison of taxon-specific abundance patterns between ecological zones differentiated by hydrological controls.Results: An unexpected paucity of primary vectors was revealed, with An. gambiae s.l. and An. funestus representing < 2% of 995 sequenced anophelines. Potential secondary vectors predominated in the vector community, primarily An. coustani group species and An. squamosus. Whilst the distribution of An. gambiae s.l. in the study area was highly clustered, secondary vector species were ubiquitous across the landscape in both dry and wet seasons, with some taxon-specific relationships between abundance and ecological zones by season.Conclusions: Larval survey results imply that residual transmission of malaria in Barotseland is being mediated predominantly by secondary vector species, whose known tendencies for crepuscular and outdoor biting renders them largely insensitive to prevalent vector control methods (ITNs and IRS). Alternative interventions may be required against this vector community to further reduce transmission. Larviciding is one potential supplementary intervention, although it presents a challenge in extensive wetlands such as those found in the Upper Zambezi catchment. However, the combination of advances in remote sensing of habitats, genetic identification of local vectors, and spatial modelling present a potential opportunity to optimise targeting of aerial spraying in these environments.

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Anopheles mosquito surveillance in Madagascar reveals multiple blood feeding behavior and Plasmodium infection

Cited by 34 publications

References 60 publications

Differential contribution of Anopheles coustani and Anopheles arabiensis to the transmission of Plasmodium falciparum and Plasmodium vivax in two neighbouring villages of Madagascar

Differential contribution of Anopheles coustani and Anopheles arabiensis to the transmission of Plasmodium falciparum and Plasmodium vivax in two neighbouring villages of Madagascar

Mapping malaria seasonality in Madagascar using health facility data

Geographically extensive larval surveys reveal an unexpected scarcity of primary vector mosquitoes in a region of persistent malaria transmission in western Zambia

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