Vector bionomics and malaria transmission in the Upper Orinoco River, Southern Venezuela

Characterization of larval habitats of Anopheles (Nyssorhynchus) darlingi and associated species in malaria areas in western Brazilian Amazon

BACKGROUND

Anopheles darlingi is the most efficient vector of malaria parasites in the Neotropics. Nevertheless, the specificities of its larval habitats are still poorly known.

OBJECTIVES

Characterize permanent larval habitats, and population dynamics of An. darlingi and other potential vectors in relation to climate, physicochemical variables, insect fauna and malaria cases.

METHODS

A 14-month longitudinal study was conducted in Porto Velho, Rondônia, western Brazilian Amazon. Monthly, 21 permanent water bodies were sampled. Immature anophelines and associated fauna were collected, physicochemical characteristics, and climate variables were recorded and analyzed.

FINDINGS

Five types of habitats were identified: lagoon, stream, stream combined with lagoon, stream combined with dam, and fishpond. A total of 60,927 anophelines were collected. The most abundant species in all habitats were Anopheles braziliensis and An. darlingi. The highest density was found in the lagoon, while streams had the highest species richness. Abundance was higher during the transition period wet-dry season. There was a lag of respectively four and five months between the peak of rainfall and the Madeira River level and the highest abundance of An. darlingi larvae, which were positively correlated with habitats partially shaded, pH close to neutrality, increase dissolved oxygen and sulphates.

MAIN CONCLUSIONS

The present study provides data on key factors defining permanent larval habitats for the surveillance of An. darlingi and other potential vectors as well as a log-linear Negative Binomial model based on immature mosquito abundance and climate variables to predict the increase in the number of malaria cases.

Blood feeding habits of mosquitoes: hardly a bite in South America

Mosquito blood feeding plays a key role in epidemiology. Despite its importance and large number of studies worldwide, less attention has been paid in South America. We summarized some general concepts and methodological issues related to the study of mosquito blood feeding habits, and compiled and analyzed all published information regarding the subject in the continent until 2020. Available literature comprised 152 scientific studies, that pursued different approaches: human landing catches (102 studies), baited trap (19), and blood meal analyses of collected specimens (38). Among the latter, 23 used serological and 15 molecular techniques. Species most frequently studied were those incriminated in malaria transmission, whereas relevant vectors such as Aedes aegypti, Ae. albopictus, and Haemagogus janthinomys were surprisingly neglected. Brazil was the leading country both in number of works and species studied. For over 70% of the species and three out of 13 South American countries there is no single information on mosquito blood feeding habits. Data from baited traps included 143 mosquito species, 83.9% of which were attracted to humans, either exclusively (10.5%) or in combination with other vertebrates (73.4%). Host blood identification of field collected specimens provided data on 102 mosquito species, and 60.8% of these fed on humans (55.9% combined with other vertebrates). Only 17 of the 73 species assessed by both methods yielded similar feeding patterns. Finally, supplementary tables are provided in a comprehensive summary of all information available and information gaps are highlighted for future research in the continent.

Adult damselflies as possible regulators of mosquito populations in urban areas

BACKGROUND

Dragonfly and damselfly larvae have been considered as possible biocontrol agents against young instars of mosquito vectors in urban environments. Yet our knowledge about adult odonate predation against mosquito adults is scarce. We quantified daily and annual predation rates, consumption rates and prey preferences of adult Hetaerina vulnerata male damselflies in an urban park. A focus on predation of mosquito species was provided, quantified their arbovirus (dengue, chikungunya and Zika) infection rates and biting activity.

RESULTS

Foraging times of H. vulnerata overlapped with those of the maximum activity of hematophagous mosquitoes. The most consumed preys were Diptera and Hymenoptera and, in lower quantities, Hemiptera, Coleoptera, Trichoptera, Psocoptera and Neuroptera. Of note, 7% of the diet was represented by hematophagous dipterans, with 2.4% being Aedes aegypti and Aedes albopictus. Prey abundance in the diet coincided with that of the same species in the environment. The arboviral infection rate (dengue, chikungunya and Zika) was 1.6% for A. aegypti and A. albopictus. The total biting rate of these mosquito vectors was 16 bites per person per day, while the annual rate of infectious bites was 93.4.

CONCLUSION

Although 2.4% for both Aedes species seems a low consumption, considering the presence of 12 odonate species at the park, it can be argued that adult odonates may play a relevant role as mosquito vector regulators, therefore impacting the spread of mosquito-borne diseases. Our study outlines the need for further research on the topic of the possible role of adult odonates for mosquito biocontrol. © 2021 Society of Chemical Industry.

The malaria burden of Amerindian groups of three Venezuelan states: a descriptive study based on programmatic data

Background

Fifty-three percent of all cases of malaria in the Americas in 2019 came from Venezuela, where the epidemic is heavily focused south of the Orinoco river, and where most of the country’s Amerindian groups live. Although the disease is known to represent a significant public health problem among these populations, little epidemiological data exists on the subject. This study aims to provide information on malaria incidence, geospatial clustering, and risk factors associated to Plasmodium falciparum infection among these groups.

Methods

This is a descriptive study based on the analysis of published and unpublished programmatic data collected by Venezuelan health authorities and non-government organizations between 2014 and 2018. The Annual Parasite Index among indigenous groups (API-i) in municipalities of three states (Amazonas, Bolivar, and Sucre) were calculated and compared using the Kruskal Wallis test, risk factors for Plasmodium falciparum infection were identified via binomial logistic regression and maps were constructed to identify clusters of malaria cases among indigenous patients via Moran’s I and Getis-Ord’s hot spot analysis.

Results

116,097 cases of malaria in Amerindian groups were registered during the study period. An increasing trend was observed between 2014 and 2016 but reverted in 2018. Malaria incidence remains higher than in 2014 and hot spots were identified in the three states, although more importantly in the south of Bolivar. Most cases (73.3%) were caused by Plasmodium vivax, but the Hoti, Yanomami, and Eñepa indigenous groups presented higher odds for infection with Plasmodium falciparum.

Conclusion

Malaria cases among Amerindian populations increased between 2014 and 2018 and seem to have a different geographic distribution than those among the general population. These findings suggest that tailored interventions will be necessary to curb the impact of malaria transmission in these groups.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-021-03819-7.

Natural malaria infection in anophelines vectors and their incrimination in local malaria transmission in Darién, Panama

Background

More than 85% of the malaria cases in Panama occur in poor, rural and indigenous regions like Darien Province. Vector diversity, infection rate and spatial distribution are important entomological parameters of malaria transmission dynamics. Their understanding is crucial for the development of effective disease control strategies. The objective of this study was to determine the composition of Anopheles species, their natural infection rate and their geographic distribution to better understand the malaria transmission dynamics in Darién, Panama.

Methods

Anophelines mosquitoes were captured during the rainy and dry season of 2016. We selected five communities where adult anophelines were collected using CDC light-traps, and through protective human-baited traps. Detection of natural infection and Plasmodium genotype were detected via nested PCR through the amplification of ssrRNA and the circumsporozoite protein gene (csp), respectively.

Results

A total of 1,063 mosquitoes were collected mosquitoes were collected for the detection of natural infection with Plasmodium spp. Nine Anophelines species were identified, with the predominant species being: An. (Nys.) darlingi (45.0%) and An. (Nys.) albimanus (42.6%). Natural infection in An. (Nys.) albimanus with P. vivax was detected in one mosquito pool from the community Pueblo Tortuga (0.6%), three from Marraganti (1.7%), two from Bajo Chiquito (1.1%) and three pools from Alto Playona 3 (1.7%). For An. (Nys.) darlingi mosquitoes, we detected seven positive pools from the community Bajo Chiquito (4.0%), two pools from Marraganti (1.1%) and two pools from Alto Playona (1.1%). The P. vivax allelic variant VK210 was detected in infected mosquitoes.

Conclusion

The results from this study provide new information on the transmission dynamics associated with anophelines vectors in the Darién region. This is the first report of natural P. vivax infection in An. (Nys.) darlingi and its incrimination as a potential malaria vector in this region of Panama. Additional studies are necessary to expand our knowledge and determine crucial parameters in malaria transmission in Darién, which in turn will aid the National Malaria Program in attaining an adequate malaria control strategy towards malaria elimination.

Malaria in Southern Venezuela: The hottest hotspot in Latin America

Malaria elimination in Latin America is becoming an elusive goal. Malaria cases reached a historical ~1 million in 2017 and 2018, with Venezuela contributing 53% and 51% of those cases, respectively. Historically, malaria incidence in southern Venezuela has accounted for most of the country's total number of cases. The efficient deployment of disease prevention measures and prediction of disease spread to new regions requires an in-depth understanding of spatial heterogeneity on malaria transmission dynamics. Herein, we characterized the spatial epidemiology of malaria in southern Venezuela from 2007 through 2017 and described the extent to which malaria distribution has changed country-wide over the recent years. We found that disease transmission was focal and more prevalent in the southeast region of southern Venezuela where two persistent hotspots of Plasmodium vivax (76%) and P. falciparum (18%) accounted for ~60% of the total number of cases. Such hotspots are linked to deforestation as a consequence of illegal gold mining activities. Incidence has increased nearly tenfold over the last decade, showing an explosive epidemic growth due to a significant lack of disease control programs. Our findings highlight the importance of spatially oriented interventions to contain the ongoing malaria epidemic in Venezuela. This work also provides baseline epidemiological data to assess cross-border malaria dynamics and advocates for innovative control efforts in the Latin American region.

Vector-Focused Approaches to Curb Malaria Transmission in the Brazilian Amazon: An Overview of Current and Future Challenges and Strategies

In Brazil, malaria transmission is mostly confined to the Amazon, where substantial progress has been made towards disease control in the past decade. Vector control has been historically considered a fundamental part of the main malaria control programs implemented in Brazil. However, the conventional vector-control tools have been insufficient to control or eliminate local vector populations due to the complexity of the Amazonian rainforest environment and ecological features of malaria vector species in the Amazon, especially Anopheles darlingi. Malaria elimination in Brazil and worldwide eradication will require a combination of conventional and new approaches that takes into account the regional specificities of vector populations and malaria transmission dynamics. Here we present an overview on both conventional and novel promising vector-focused tools to curb malaria transmission in the Brazilian Amazon. If well designed and employed, vector-based approaches may improve the implementation of malaria-control programs, particularly in remote or difficult-to-access areas and in regions where existing interventions have been unable to eliminate disease transmission. However, much effort still has to be put into research expanding the knowledge of neotropical malaria vectors to set the steppingstones for the optimization of conventional and development of innovative vector-control tools.

Seasonal pattern of malaria cases and the relationship with hydrologic variability in the Amazonas State, Brazil

INTRODUCTION

Malaria is an infectious disease of high transmission in the Amazon region, but its dynamics and spatial distribution may vary depending on the interaction of environmental, socio-cultural, economic, political and health services factors.

OBJECTIVE

To verify the existence of malaria case patterns in consonance with the fluviometric regimes in Amazon basin.

METHOD

Methods of descriptive and inferential statistics were used in malaria and water level data for 35 municipalities in the Amazonas State, in the period from 2003 to 2014.

RESULTS

The existence of a tendency to modulate the seasonality of malaria cases due to distinct periods of rivers flooding has been demonstrated. Differences were observed in the annual hydrological variability accompanied by different patterns of malaria cases, showing a trend of remodeling of the epidemiological profile as a function of the flood pulse.

CONCLUSION

The study suggests the implementation of regional and local strategies considering the hydrological regimes of the Amazon basin, enabling municipal actions to attenuate the malaria in the Amazonas State.

Behavior and abundance of Anopheles darlingi in communities living in the Colombian Amazon riverside

In the past few years, relative frequencies of malaria parasite species in communities living in the Colombian Amazon riverside have changed, being Plasmodium vivax (61.4%) and Plasmodium malariae (43.8%) the most frequent. Given this epidemiological scenario, it is important to determine the species of anophelines involved in these parasites' transmission. This study was carried out in June 2016 in two indigenous communities living close to the tributaries of the Amazon River using protected human bait. The results of this study showed a total abundance of 1,085 mosquitos, of which 99.2% corresponded to Anopheles darlingi. Additionally, only two anopheline species were found, showing low diversity in the study areas. Molecular confirmation of some individuals was then followed by evolutionary analysis by using the COI gene. Nested PCR was used for identifying the three Plasmodium species circulating in the study areas. Of the two species collected in this study, 21.0% of the An. darlingi mosquitoes were infected with P. malariae, 21.9% with P. vivax and 10.3% with Plasmodium falciparum. It exhibited exophilic and exophagic behavior in both study areas, having marked differences regarding its abundance in each community (Tipisca first sampling 49.4%, Tipisca second sampling 39.6% and Doce de Octubre 10.9%). Interestingly, An. mattogrossensis infected by P. vivax was found for the first time in Colombia (in 50% of the four females collected). Analysis of An. darlingi COI gene diversity indicated a single population maintaining a high gene flow between the study areas. The An. darlingi behavior pattern found in both communities represents a risk factor for the region's inhabitants living/working near these sites. This highlights the need for vector control efforts such as the use of personal repellents and insecticides for use on cattle, which must be made available in order to reduce this Anopheline's abundance.

Variability in malaria cases and the association with rainfall and rivers water levels in Amazonas State, Brazil

Understanding the relations between rainfall and river water levels and malaria cases can provide important clues on modulation of the disease in the context of local climatic variability. In order to demonstrate how these relations can vary in the same endemic space, a coherence and wavelet phase analysis was performed between environmental and epidemiological variables from 2003 to 2010 for 8 municipalities (counties) in the state of Amazonas, Brazil (Barcelos, Borba, Canutama, Carauari, Coari, Eirunepé, Humaitá, and São Gabriel da Cachoeira). The results suggest significant coherences, mainly on the scale of annual variability, but scales of less than 1 year and of 2 years were also found. The analyses show that malaria cases display a peak at approximately 1 and a half months before or after peak rainfall and on average 1-4 months after peak river water levels in most of the municipalities studied. Each environmental variable displayed distinct local behavior in time and in space, suggesting that other local variables (e.g. topography) may control environmental conditions, favoring different patterns in each municipality. However, when the analyses were performed jointly it was possible to show a non-random order in these relations. Although environmental and climatic factors indicate a certain influence on malaria dynamics, surveillance, prevention, and control issues should not be overlooked, meaning that government public health interventions can mask possible relations with local hydrological and climatic conditions.

Abundance of impacted forest patches less than 5 km2 is a key driver of the incidence of malaria in Amazonian Brazil

The precise role that deforestation for agricultural settlements and commercial forest products plays in promoting or inhibiting malaria incidence in Amazonian Brazil is controversial. Using publically available databases, we analyzed temporal malaria incidence (2009–2015) in municipalities of nine Amazonian states in relation to ecologically defined variables: (i) deforestation (rate of forest clearing over time); (ii) degraded forest (degree of human disturbance and openness of forest canopy for logging) and (iii) impacted forest (sum of deforested and degraded forest patches). We found that areas affected by one kilometer square of deforestation produced 27 new malaria cases (r² = 0.78; F1,10 = 35.81; P < 0.001). Unexpectedly, we found both a highly significant positive correlation between number of impacted forest patches less than 5 km² and malaria cases, and that these patch sizes accounted for greater than ~95% of all patches in the study area. There was a significantly negative correlation between extraction forestry economic indices and malaria cases. Our results emphasize not only that deforestation promotes malaria incidence, but also that it directly or indirectly results in a low Human Development Index, and favors environmental conditions that promote malaria vector proliferation.

Environmental variables associated with anopheline larvae distribution and abundance in Yanomami villages within unaltered areas of the Brazilian Amazon

BACKGROUND

Many indigenous villages in the Amazon basin still suffer from a high malaria burden. Despite this health situation, there are few studies on the bionomics of anopheline larvae in such areas. This publication aims to identify the main larval habitats of the most abundant anopheline species and to assess their associations with some environmental factors.

METHODS

We conducted a 19-month longitudinal study from January 2013 to July 2014, sampling anopheline larvae in two indigenous Yanomami communities, comprised of four villages each. All natural larval habitats were surveyed every two months with a 350 ml manual dipper, following a standardized larval sampling methodology. In a third study area, we conducted two field expeditions in 2013 followed by four systematic collections during the long dry season of 2014-2015.

RESULTS

We identified 177 larval habitats in the three study areas, from which 9122 larvae belonging to 13 species were collected. Although species abundance differed between villages, An. oswaldoi (s.l.) was overall the most abundant species. Anopheles darlingi, An. oswaldoi (s.l.), An. triannulatus (s.s.) and An. mattogrossensis were primarily found in larval habitats that were partially or mostly sun-exposed. In contrast, An. costai-like and An. guarao-like mosquitoes were found in more shaded aquatic habitats. Anopheles darlingi was significantly associated with proximity to human habitations and larval habitats associated with river flood pulses and clear water.

CONCLUSIONS

This study of anopheline larvae in the Brazilian Yanomami area detected high heterogeneities at micro-scale levels regarding species occurrence and densities. Sun exposure was a major modulator of anopheline occurrence, particularly for An. darlingi. Lakes associated with the rivers, and particularly oxbow lakes, were the main larval habitats for An. darlingi and other secondary malaria vectors. The results of this study will serve as a basis to plan larval source management activities in remote indigenous communities of the Amazon, particularly for those located within low-order river-floodplain systems.

Genetic structure and phenotypic variation of Anopheles darlingi in northwest Colombia

This study evaluated the influence of environmental heterogeneity on Anopheles darlingi genetic and morphometric traits at a microgeographic level. Specimens of An. darlingi collected from multiple municipalities in the Colombian malaria endemic region Urabá-Bajo Cauca and Alto Sinú (UCS) were analyzed using 13 microsatellite loci. Spatial genetic structure, population variation and wing geometric morphometric analyses were performed. Microsatellite results showed low genetic differentiation and high gene flow among populations; four highly admixed subpopulations were detected with no particular association to the municipalities. Wing geometric morphometrics analysis showed a subtle but significant difference in wing shape for El Bagre vs. Mutatá populations, possibly influenced by geographical distance. Discrimination among populations in the morphospace showed a slight separation of the Tierralta population. There was no significant correlation between the genetic and geographic or genetic and environmental distances. We hypothesize that environmental heterogeneity in the UCS region does not reach a threshold to affect population structure of An. darlingi. Another possibility is that microsatellites are not sensitive enough to detect existing structure. It remains to be determined which local factors govern phenotypic variation among these populations and how, or whether these may affect mosquito biology and transmission capacity.

Potential distribution of mosquito vector species in a primary malaria endemic region of Colombia

Rapid transformation of natural ecosystems changes ecological conditions for important human disease vector species; therefore, an essential task is to identify and understand the variables that shape distributions of these species to optimize efforts toward control and mitigation. Ecological niche modeling was used to estimate the potential distribution and to assess hypotheses of niche similarity among the three main malaria vector species in northern Colombia: Anopheles nuneztovari, An. albimanus, and An. darlingi. Georeferenced point collection data and remotely sensed, fine-resolution satellite imagery were integrated across the Urabá -Bajo Cauca-Alto Sinú malaria endemic area using a maximum entropy algorithm. Results showed that An. nuneztovari has the widest geographic distribution, occupying almost the entire study region; this niche breadth is probably related to the ability of this species to colonize both, natural and disturbed environments. The model for An. darlingi showed that most suitable localities for this species in Bajo Cauca were along the Cauca and Nechí river. The riparian ecosystems in this region and the potential for rapid adaptation by this species to novel environments, may favor the establishment of populations of this species. Apparently, the three main Colombian Anopheles vector species in this endemic area do not occupy environments either with high seasonality, or with low seasonality and high NDVI values. Estimated overlap in geographic space between An. nuneztovari and An. albimanus indicated broad spatial and environmental similarity between these species. An. nuneztovari has a broader niche and potential distribution. Dispersal ability of these species and their ability to occupy diverse environmental situations may facilitate sympatry across many environmental and geographic contexts. These model results may be useful for the design and implementation of malaria species-specific vector control interventions optimized for this important malaria region.

Spatial and Seasonal Dynamics of Anopheles Mosquitoes in Saint-Georges de l'Oyapock, French Guiana: Influence of Environmental Factors

Little is known about the Anopheles fauna of Saint-Georges de l'Oyapock, a persistent malaria-endemic municipality in French Guiana. This study aimed to update the knowledge of local Anopheles diversity, and their ecology and role in malaria transmission. Sampling sessions were implemented between September 2013 and October 2014. Four species were identified from the 3,450 specimens collected: Anopheles darlingi Root, An. braziliensis, An. triannulatus s.l., and An. nuneztovari s.l. Anopheles darlingi was the predominant species. Its involvement in malaria transmission was suspected due to 1) its abundance, 2) the presence of a density peak during the malaria emergence period, and 3) a dynamic correlated with malaria cases observed two months later. Present and past studies show that the influence of environmental conditions on malaria vector dynamics is high, and may vary drastically according to the local context. This supports evidence that control strategies must be designed at fine scales.

High malaria transmission in a forested malaria focus in French Guiana: How can exophagic Anopheles darlingi thwart vector control and prevention measures?

In French Guiana, malaria vector control and prevention relies on indoor residual spraying and distribution of long lasting insecticidal nets. These measures are based on solid epidemiological evidence but reveal a poor understanding of the vector. The current study investigated the behaviour of both vectors and humans in relation to the ongoing prevention strategies. In 2012 and 2013, Anopheles mosquitoes were sampled outdoors at different seasons and in various time slots. The collected mosquitoes were identified and screened for Plasmodium infection. Data on human behaviour and malaria episodes were obtained from an interview. A total of 3,135 Anopheles mosquitoes were collected, of which Anopheles darlingi was the predominant species (96.2%). For the December 2012-February 2013 period, the Plasmodium vivax infection rate for An. darlingi was 7.8%, and the entomological inoculation rate was 35.7 infective bites per person per three-month span. In spite of high bednet usage (95.7%) in 2012 and 2013, 52.2% and 37.0% of the participants, respectively, had at least one malaria episode. An. darlingi displayed heterogeneous biting behaviour that peaked between 20:30 and 22:30; however, 27.6% of the inhabitants were not yet protected by bednets by 21:30. The use of additional individual and collective protective measures is required to limit exposure to infective mosquito bites and reduce vector densities.

Anopheles species composition explains differences in Plasmodium transmission in La Guajira, northern Colombia

Malaria in La Guajira, the most northern state of Colombia, shows two different epidemiological patterns. Malaria is endemic in the municipality of Dibulla whereas in Riohacha it is characterised by sporadic outbreaks. This study aimed to establish whether differences in transmission patterns could be attributed to different vector species. The most abundant adult female species were Anopheles aquasalis, exclusive to Riohacha, and Anopheles darlingi, restricted to Dibulla. Anopheles mosquitoes were identified using morphology and the molecular markers internal transcribed spacer 2 and cytochrome c oxidase I. All specimens (n = 1,393) were tested by ELISA to determine natural infection rates with Plasmodium falciparum and Plasmodium vivax. An. darlingi was positive for P. vivax 210, with an infection rate of 0.355% and an entomological inoculation rate of 15.87 infective bites/person/year. Anopheles albimanus larvae were the most common species in Riohacha, found in temporary swamps; in contrast, in Dibulla An. darlingi were detected mainly in permanent streams. Distinctive species composition and larval habitats in each municipality may explain the differences in Plasmodium transmission and suggest different local strategies should be used for vector control.

Malaria Control in Amerindian Communities of Venezuela : Strengthening Ecohealth Practice Throughout Conservation Science and Capability Approach

Adaptive management and ecohealth frameworks were developed for malaria elimination in Amerindian riparian communities of Venezuela. These frameworks were developed as a strategy to capture, organize, and communicate connections among key factors related to local malaria complex systems. Important causal relationships between social, economic, and environmental stressors which are determinant of malaria were identified at different levels and assumptions that guide interventions are offered, based on available scientific knowledge and input from stakeholders. Drawing on our experience of action research committed to the health of Amerindian populations and conservation of areas with biodiversity value, the authors provide lessons to strengthen the practice of an ecohealth approach. First, conservation targets were considered as a way to achieve sustainable human well-being rather than as a consequence of well-being. Second, the effectiveness and sustainability of technical solutions generally proposed for malaria control depend largely on individual knowledge, attitudes, and practices. Hence, it is necessary to look at the real opportunities of choices that Amerindian people have for attaining a life without malaria, and therefore pay attention to local capabilities, needs, and freedom to choose. The ecohealth approach can benefit from the capability approach, and we explain why.

Early biting and insecticide resistance in the malaria vector Anopheles might compromise the effectiveness of vector control intervention in Southwestern Uganda

Background

Southwestern Uganda has high malaria heterogeneity despite moderate vector control and other interventions. Moreover, the early biting transmission and increased resistance to insecticides might compromise strategies relying on vector control. Consequently, monitoring of vector behaviour and insecticide efficacy is needed to assess the effectiveness of strategies aiming at malaria control. This eventually led to an entomological survey in two villages with high malaria prevalence in this region.

Methods

During rainy, 2011 and dry season 2012, mosquitoes were collected in Engari and Kigorogoro, Kazo subcounty, using human landing collection, morning indoor resting collection, pyrethrum spray collection and larval collection. Circumsporozoite protein of Plasmodium falciparum sporozoites in female Anopheles mosquitoes was detected using ELISA assay. Bioassays to monitor Anopheles resistance to insecticides were performed.

Results

Of the 1,021 female Anopheles species captured, 62% (632) were Anopheles funestus and 36% (371) were Anopheles gambiae s.l. The most common species were Anopheles gambiae s.l. in Engari (75%) and A. funestus in Kigorogoro (83%). Overall, P. falciparum prevalence was 2.9% by ELISA. The daily entomological inoculation rates were estimated at 0.17 and 0.58 infected bites/person/night during rainy and dry season respectively in Engari, and 0.81 infected bites/person/night in Kigorogoro during dry season. In both areas and seasons, an unusually early evening biting peak was observed between 6 - 8 p.m. In Engari, insecticide bioassays showed 85%, 34% and 12% resistance to DDT during the rainy season, dry season and to deltamethrin during the dry season, respectively. In Kigorogoro, 13% resistance to DDT and to deltamethrin was recorded. There was no resistance observed to bendiocarb and pirimiphos methyl.

Conclusions

The heterogeneity of mosquito distribution, entomological indicators and resistance to insecticides in villages with high malaria prevalence highlight the need for a long-term vector control programme and monitoring of insecticide resistance in Uganda. The early evening biting habits of Anopheles combined with resistance to DDT and deltamethrin observed in this study suggest that use of impregnated bed nets alone is insufficient as a malaria control strategy, urging the need for additional interventions in this area of high transmission.

Preliminary biological studies on larvae and adult Anopheles mosquitoes (Diptera: Culicidae) in Miraflores, a malaria endemic locality in Guaviare department, Amazonian Colombia

In the malaria endemic municipality of Miraflores in southeastern Amazonian Colombia, several aspects of the biology of local Anopheles species were investigated to supplement the limited entomological surveillance information available and to provide baseline data for malaria prevention and vector control. Anopheles darlingi Root, 1926 was the most abundant species (95.6%), followed by Anopheles braziliensis (Chagas) (3.6%) and Anopheles oswaldoi s.l. (Peryassu) (0.7%). During the dry season, exophagic activity was prevalent only between 1800-2100 hours; after this (2100-0600 hours) only endophagy was encountered. In contrast, during the rainy season, both endophagy and exophagy occurred throughout the collection period. The human biting rate for An. darlingi was 8.6. This species was positive for Plasmodium vivax VK210 with a sporozoite rate = 0.13 (1/788). Breeding sites corresponded to stream (n = 7), flooded excavations (n = 4), flooded forest (n = 1), wetlands (n = 2), and an abandoned water reservoir (n = 1). An. darlingi predominated in these sites in both seasons. Based on these data, An. darlingi is the main local malaria vector, and we recommend that local prevention and control efforts focus on strengthening entomological surveillance to determine potential changes of species biting behavior and time to reduce human-vector interactions.

Malaria vectors in San José del Guaviare, Orinoquia, Colombia

This study was conducted to determine Anopheles species composition and their natural infectivity by human Plasmodium in 2 localities with the highest malaria transmission in San Jose del Guaviare, Guaviare, Colombia. A total of 1,009 Anopheles mosquitoes were collected using human landing catches during 8 months in 2010. Anopheles darlingi was the most abundant (83.2%) followed by An. albitarsis s.l. (8.6%), Anopheles braziliensis (3.8%), An. oswaldoi s.l. (1%), and An. rangeli (0.3%). Anopheles darlingi showed the highest human biting rate, and it was found naturally infected with Plasmodium vivax VK210 (0.119%) using enzyme-linked immunosorbent assays. All species were collected biting both indoors and outdoors. Anopheles darlingi showed biting activity overnight with an indoor peak between 1200-0100 h. Therefore, we recommend that malaria prevention strategies focus on 1) insecticide-treated nets to reduce human-vector contact when people are most exposed and unprotected; 2) accurate diagnoses; 3) adequate treatment for patients; 4) more timely epidemiological notification; and 5) improved entomological surveillance.

Malaria entomological risk factors in relation to land cover in the Lower Caura River Basin, Venezuela

To explore the effects of deforestation and resulting differences in vegetation and land cover on entomological parameters, such as anopheline species composition, abundance, biting rate, parity and entomological inoculation rate (EIR), three villages were selected in the Lower Caura River Basin, state of Bolívar, Venezuela. All-night mosquito collections were conducted between March 2008-January 2009 using CDC light traps and Mosquito Magnet® Liberty Plus. Human landing catches were performed between 06:00 pm-10:00 pm, when anophelines were most active. Four types of vegetation were identified. The Annual Parasite Index was not correlated with the type of vegetation. The least abundantly forested village had the highest anopheline abundance, biting rate and species diversity. Anopheles darlingi and Anopheles nuneztovari were the most abundant species and were collected in all three villages. Both species showed unique biting cycles. The more abundantly forested village of El Palmar reported the highest EIR. The results confirmed previous observations that the impacts of deforestation and resulting changes in vegetation cover on malaria transmission are complex and vary locally.

Environmental change and the dynamics of parasitic diseases in the Amazon

The Amazonian environment is changing rapidly, due to deforestation, in the short term, and, climatic change is projected to alter its forest cover, in the next few decades. These modifications to the, environment have been altering the dynamics of infectious diseases which have natural foci in the, Amazonian biome, especially in its forest. Current land use practices which are changing the, epidemiological profile of the parasitic diseases in the region are road building; logging; mining; expansion of agriculture and cattle ranching and the building of large dams. Malaria and the cutaneous, leishmaniasis are the diseases best known for their rapid changes in response to environmental, modifications. Others such as soil-transmitted helminthiases, filarial infections and toxoplasmosis, which have part of their developmental cycles in the biophysical environment, are also expected to, change rapidly. An interdisciplinary approach and an integrated, international surveillance are needed, to manage the environmentally-driven changes in the Amazonian parasitic diseases in the near future.

The periodicity of Plasmodium vivax and Plasmodium falciparum in Venezuela

We investigated the periodicity of Plasmodium vivax and P. falciparum incidence in time-series of malaria data (1990-2010) from three endemic regions in Venezuela. In particular, we determined whether disease epidemics were related to local climate variability and regional climate anomalies such as the El Niño Southern Oscillation (ENSO). Malaria periodicity was found to exhibit unique features in each studied region. Significant multi-annual cycles of 2- to about 6-year periods were identified. The inter-annual variability of malaria cases was coherent with that of SSTs (ENSO), mainly at temporal scales within the 3-6 year periods. Additionally, malaria cases were intensified approximately 1 year after an El Niño event, a pattern that highlights the role of climate inter-annual variability in the epidemic patterns. Rainfall mediated the effect of ENSO on malaria locally. Particularly, rains from the last phase of the season had a critical role in the temporal dynamics of Plasmodium. The malaria-climate relationship was complex and transient, varying in strength with the region and species. By identifying temporal cycles of malaria we have made a first step in predicting high-risk years in Venezuela. Our findings emphasize the importance of analyzing high-resolution spatial-temporal data to better understand malaria transmission dynamics.

Dynamics of forest malaria transmission in Balaghat district, Madhya Pradesh, India

Background

An epidemiological and entomological study was carried out in Balaghat district, Madhya Pradesh, India to understand the dynamics of forest malaria transmission in a difficult and hard to reach area where indoor residual spray and insecticide treated nets were used for vector control.

Methods

This community based cross-sectional study was undertaken from January 2010 to December 2012 in Baihar and Birsa Community Health Centres of district Balaghat for screening malaria cases. Entomological surveillance included indoor resting collections, pyrethrum spray catches and light trap catches. Anophelines were assayed by ELISA for detection of Plasmodium circumsporozoite protein.

Findings

Plasmodium falciparum infection accounted for >80% of all infections. P. vivax 16.5%, P. malariae 0.75% and remaining were mixed infections of P. falciparum, P. vivax and P. malariae. More than, 30% infections were found in infants under 6 months of age. Overall, an increasing trend in malaria positivity was observed from 2010 to 2012 (chi-square for trend  =  663.55; P<0.0001). Twenty five Anopheles culicifacies (sibling species C, D and E) were positive for circumsporozoite protein of P. falciparum (44%) and P. vivax (56%). Additionally, 2 An. fluviatilis, were found positive for P. falciparum and 1 for P. vivax (sibling species S and T). An. fluviatilis sibling species T was found as vector in forest villages for the first time in India.

Conclusion

These results showed that the study villages are experiencing almost perennial malaria transmission inspite of indoor residual spray and insecticide treated nets. Therefore, there is a need for new indoor residual insecticides which has longer residual life or complete coverage of population with long lasting insecticide treated nets or both indoor residual spray and long lasting bed nets for effective vector control. There is a need to undertake a well designed case control study to evaluate the efficacy of these interventions.

Nightly biting cycles of malaria vectors in a heterogeneous transmission area of eastern Amazonian Brazil

BACKGROUND

The biting cycle of anopheline mosquitoes is an important component in the transmission of malaria. Inter- and intraspecific biting patterns of anophelines have been investigated using the number of mosquitoes caught over time to compare general tendencies in host-seeking activity and cumulative catch. In this study, all-night biting catch data from 32 consecutive months of collections in three riverine villages were used to compare biting cycles of the five most abundant vector species using common statistics to quantify variability and deviations of nightly catches from a normal distribution.

METHODS

Three communities were selected for study. All-night human landing catches of mosquitoes were made each month in the peridomestic environment of four houses (sites) for nine consecutive days from April 2003 to November 2005. Host-seeking activities of the five most abundant species that were previously captured infected with Plasmodium falciparum, Plasmodium malariae or Plasmodium vivax, were analysed and compared by measuring the amount of variation in numbers biting per unit time (co-efficient of variation, V), the degree to which the numbers of individuals per unit time were asymmetrical (skewness = g1) and the relative peakedness or flatness of the distribution (kurtosis = g2). To analyse variation in V, g1, and g2 within species and villages, we used mixed model nested ANOVAs (PROC GLM in SAS) with independent variables (sources of variation): year, month (year), night (year X month) and collection site (year X month).

RESULTS

The biting cycles of the most abundant species, Anopheles darlingi, had the least pronounced biting peaks, the lowest mean V values, and typically non-significant departures from normality in g1 and g2. By contrast, the species with the most sharply defined crepuscular biting peaks, Anopheles marajoara, Anopheles nuneztovari and Anopheles triannulatus, showed high to moderate mean V values and, most commonly, significantly positive skewness (g1) and kurtosis (g2) moments. Anopheles intermedius was usually, but not always, crepuscular in host seeking, and showed moderate mean V values and typically positive skewness and kurtosis. Among sites within villages, significant differences in frequencies of departures from normality (g1 and g2) were detected for An. marajoara and An. darlingi, suggesting that local environments, such as host availability, may affect the shape of biting pattern curves of these two species.

CONCLUSIONS

Analyses of co-efficients of variation, skewness and kurtosis facilitated quantitative comparisons of host-seeking activity patterns that differ among species, sites, villages, and dates. The variable and heterogeneous nightly host-seeking behaviours of the five exophilic vector species contribute to the maintenance of stable malaria transmission in these Amazonian villages. The abundances of An. darlingi and An. marajoara, their propensities to seek hosts throughout the night, and their ability to adapt host-seeking behaviour to local environments, contribute to their impact as the most important of these vector species.

Hyperendemic malaria transmission in areas of occupation-related travel in the Peruvian Amazon

Background

Plasmodium vivax and Plasmodium falciparum cause a significant illness burden in Peru. Anopheline indices for populated communities in the peri-Iquitos region of Loreto have been reported to be remarkably low, with entomological inoculation rates (EIR) estimated at one to 30 infective bites per year based on a few studies in close proximity to the urban centre of Iquitos and surrounding deforested areas. Local reports suggest that a large number of the reported cases are contracted outside of populated communities in undeveloped riverine areas frequented by loggers and fishermen.

Methods

To better understand vectorial capacity in suspected high malaria transmission zones in a rural district near Iquitos, Peru, mosquito collections were conducted at different points in the seasonality of malaria transmission in 21 sites frequented by occupational labourers. Prevalence of Plasmodium spp in vectors was determined by circumsporozoite protein ELISA on individual mosquitoes. Slide surveillance was performed for humans encountered in the zone.

Results

In total, of 8,365 adult female mosquitoes examined, 98.5% were identified as Anopheles darlingi and 117 (1.4%) tested positive for sporozoites (P. falciparum, P. vivax VK210 or P. vivax VK247). Measured human biting rates at these sites ranged from 0.102 to 41.13 bites per person per hour, with EIR values as high as 5.3 infective bites per person per night. Six percent of the 284 blood films were positive for P. vivax or P. falciparum; however, 88% of the individuals found to be positive were asymptomatic at the time of sampling.

Conclusions

The results of this study provide key missing indices of prominent spatial and temporal heterogeneity of vectorial capacity in the Amazon Basin of Peru. The identification of a target human subpopulation as a principal reservoir and dispersion source of Plasmodium species has important implications for vaccine development and the delivery of effective targeted malaria control strategies.

[Anopheles (Díptera: Culicidae) vectors of malaria in Puerto Carreño municipality, Vichada, Colombia]

INTRODUCTION

The study of the biological aspects of Anopheles spp., strengthens the entomological surveillance.

OBJECTIVE

To determine biological aspects and behavior of adult Anopheles mosquitoes in the urban area of Puerto Carreño municipality, Vichada, Colombia.

MATERIALS AND METHODS

Wild anophelines were collected landing on humans both indoors and outdoors between 18:00h and 06:00h for 50 min/h during two consecutive nights/month for eight months in the urban area of Puerto Carreño. The biting rate activity, the natural infection by Plasmodium falciparum and P. vivax VK247 and VK210 using ELISA, and the annual entomological inoculation rate were determined for each species. The members of the Albitarsis complex were determined by amplificacion of the white gene by polymerase chain reaction.

RESULTS

In order of abundance the species found were An. darlingi (n=1,166), An. marajoara sensu stricto (n=152), An. braziliensis (n=59), An. albitarsis F (n=25), An. albitarsis sensu lato (n=16), An. argyritarsis (n=3) and An. oswaldoi sensu lato (n=2). An. darlingi showed two activity peaks between 21:00 to 22:00 and 05:00 to 06:00 hours outdoors and between 21:00 to 22:00 and 04:00 to 05:00 indoors. Natural infection of this species was found with P. vivax VK210 and its annual entomological inoculation rate was 2. Natural infection of An marajoara sensu stricto with P. falciparum was found, with an annual entomological inoculation rate of 5 and a peak biting activity between 18:00 to 19:00 hrs both indoors and outdoors.

CONCLUSION

Transmission of malaria in the urban area of Puerto Carreño, Vichada, can occur by An. darlingi and An. marajoara s.s.

Malaria in South America: a drug discovery perspective

The challenge of controlling and eventually eradicating malaria means that new tools are urgently needed. South America's role in this fight spans both ends of the research and development spectrum: both as a continent capable of discovering and developing new medicines, and also as a continent with significant numbers of malaria patients. This article reviews the contribution of groups in the South American continent to the research and development of new medicines over the last decade. Therefore, the current situation of research targeting malaria control and eradication is discussed, including endemicity, geographical distribution, treatment, drug-resistance and diagnosis. This sets the scene for a review of efforts within South America to discover and optimize compounds with anti-malarial activity.

Confirmation of the occurrence of Anopheles (Nyssorhynchus) marajoara in French Guiana

Throughout the early entomological campaigns in French Guiana (1900-1945), the presence of members of the Anopheles albitarsis Complex was reported in many places across the territory. However, since then no specimen has been caught despite many entomological studies conducted on the littoral and along the main rivers in places where malaria was endemic. We report here the 1st catches in the modern period of specimens of the An. albitarsis Complex in the deep rainforest. During a military intervention, Mosquito-Magnet traps and the Centers for Disease Control and Prevention light traps were used to sample malaria vectors in an illegal gold mining area and a permanent checkpoint. Members of the An. albitarsis caught were molecularly identified using DNA barcoding. In the 2 sites where An. albitarsis s.l. were caught, all specimens were An. marajoara. As An. marajoara is considered as an important malaria vector in Amazonia, the highest interest must be shown to this species in French Guiana.

On the use of classic epidemiological formulae for estimating the intensity of endemic malaria transmission by vectors in the Amazon

Although various reports have described entomological inoculation rates of malaria vector species, most were limited to providing descriptive field data. Here, we report biting rates and survival data for two important malaria vectors in the Amazon, Anopheles darlingi (Root) and Anopheles albitarsis E (Lynch-Arribalzaga) (Diptera: Culicidae), in the state of Roraima, Brazil. We calculated theoretical sporozoite infection rates and critical vector biting rates for these species during 1 year, comprising six bimestrial collections. Anopheles darlingi had higher sporozoite rates and lower critical biting rates, indicating that it would be the more efficient vector at the beginning of epidemic malaria transmission. Our data, together with compiled information from the literature in the Amazon, suggest that epidemic malaria transmission may be initiated by the primary vector, such as A. darlingi, while secondary vectors, such as A. albitarsis E, may only become epidemiologically important when there is an increase in the prevalence of human malaria. We propose that mathematical modeling may be able to quantify the relative importance of secondary vector species in malaria epidemiology.

Anopheles (Díptera: Culicidae) vectors of malaria in Puerto Carreño municipality, Vichada, Colombia

Introducción. El estudio de los aspectos de la biología de los mosquitos Anopheles spp. fortalece la vigilancia entomológica.Objetivo. Determinar los aspectos de la biología y el comportamiento de las especies adultas del género Anopheles presentes en el área urbana de Puerto Carreño.Materiales y métodos. Se capturaron Anopheles spp. silvestres que se habían posado en personas, en el intradomicilio y peridomicilio de viviendas ubicadas en el área urbana del municipio de Puerto Carreño (Vichada), entre las 18:00 y las 06:00 horas, durante dos noches consecutivas por mes y durante ocho meses. Se determinó la actividad de picadura para cada especie, la infección natural por Plasmodium falciparum y P. vivax VK247 y VK210 mediante la técnica ELISA, y se determinó la tasa de inoculación entomológica. Los individuos pertenecientes al complejo Albitarsis se determinaron mediante amplificación en cadena de la polimerasa del fragmento del gen white.Resultados. En orden de abundancia, se encontraron: An. darlingi (n=1.166), An. marajoara sensu stricto (n=152), An. braziliensis (n=59), An. albitarsis F (n=25), An. albitarsis sensu lato (n=16), An. argyritarsis (n=3) y An. oswaldoi sensu lato (n=2). Anopheles darlingi registró dos picos de actividad de picadura entre las 21:00-22:00 y las 5:00-06:00 horas en el peridomicilio y, entre las 21:00-22:00 y las 04:00-05:00 horas, en el intradomicilio. Esta especie se encontró naturalmente infectada por P. vivax VK210 y registró una tasa de inoculación entomológica de dos para el año. Anopheles marajoara s.s. se encontró naturalmente infectado por P. falciparum y registró una tasa de inoculación entomológica de 5 para el año, con un máximo de actividad de picadura entre las 18:00 y las 19:00 horas, tanto en el intradomicilio como en el peridomicilio.Conclusión. Es posible que exista transmisión de malaria en el área urbana de Puerto Carreño (Vichada) y An. darlingi y An. marajoara s.s. serían las especies incriminadas.

Amazonian malaria: asymptomatic human reservoirs, diagnostic challenges, environmentally driven changes in mosquito vector populations, and the mandate for sustainable control strategies

Across the Americas and the Caribbean, nearly 561,000 slide-confirmed malaria infections were reported officially in 2008. The nine Amazonian countries accounted for 89% of these infections; Brazil and Peru alone contributed 56% and 7% of them, respectively. Local populations of the relatively neglected parasite Plasmodium vivax, which currently accounts for 77% of the regional malaria burden, are extremely diverse genetically and geographically structured. At a time when malaria elimination is placed on the public health agenda of several endemic countries, it remains unclear why malaria proved so difficult to control in areas of relatively low levels of transmission such as the Amazon Basin. We hypothesize that asymptomatic parasite carriage and massive environmental changes that affect vector abundance and behavior are major contributors to malaria transmission in epidemiologically diverse areas across the Amazon Basin. Here we review available data supporting this hypothesis and discuss their implications for current and future malaria intervention policies in the region. Given that locally generated scientific evidence is urgently required to support malaria control interventions in Amazonia, we briefly describe the aims of our current field-oriented malaria research in rural villages and gold-mining enclaves in Peru and a recently opened agricultural settlement in Brazil.

Spatial clustering and longitudinal variation of Anopheles darlingi (Diptera: Culicidae) larvae in a river of the Amazon: the importance of the forest fringe and of obstructions to flow in frontier malaria

Deforestation has been linked to a rise in malaria prevalence. In this paper, we studied longitudinally 20 spots, including forested and deforested portions of a temporary river in a malarigenous frontier zone. Larval habitat parameters influencing distribution of Anopheles darlingi (Diptera: Culicidae) larvae were studied. We observed that larvae were clustered in forested-deforested transitions. For the first time in the literature, it was verified that parameters determining larval distribution varied from deforested to forested areas. The proximity to human dwellings was also a significant factor determining distribution, but larvae was most importantly associated with a previously undescribed parameter, the presence of small obstructions to river flow, such as tree trunks within the river channel, which caused pooling of water during the dry season ('microdams'). In deforested areas, the most important factor determining distribution of larvae was shade (reduced luminance). Larvae were absent in the entire studied area during the wet season and present in most sites during the dry season. During the wet-dry transition, larvae were found sooner in areas with microdams, than in other areas, suggesting that flow obstruction prolongs the breeding season of An. darlingi. Adult mosquito densities and malaria incidence were higher during the dry season. Our data correlate well with the published literature, including the distribution of malaria cases near the forest fringes, and has permitted the creation of a model of An. darlingi breeding, where preference for sites with reduced luminance, human presence and microdams would interact to determine larval distribution.

Unravelling the relationships between Anopheles darlingi (Diptera: Culicidae) densities, environmental factors and malaria incidence: understanding the variable patterns of malarial transmission in French Guiana (South America)

Anopheles darlingi, one of the main malaria vectors in the Neotropics, is widely distributed in French Guiana, where malaria remains a major public-health problem. Elucidation of the relationships between the population dynamics of An. darlingi and local environmental factors would appear to be an essential factor in the epidemiology of human malaria in French Guiana and the design of effective vector-control strategies. In a recent investigation, longitudinal entomological surveys were carried out for 2-4 years in one village in each of three distinct endemic areas of French Guiana. Anopheles darlingi was always the anopheline mosquito that was most frequently caught on human bait, although its relative abundance (as a proportion of all the anophelines collected) and human biting rate (in bites/person-year) differed with the study site. Seasonality in the abundance of human-landing An. darlingi (with peaks at the end of the rainy season) was observed in only two of the three study sites. Just three An. darlingi were found positive for Plasmodium (either P. falciparum or P. vivax) circumsporozoite protein, giving entomological inoculation rates of 0·0-8·7 infectious bites/person-year. Curiously, no infected An. darlingi were collected in the village with the highest incidence of human malaria. Relationships between malaria incidence, An. darlingi densities, rainfall and water levels in the nearest rivers were found to be variable and apparently dependent on land-cover specificities that reflected the diversity and availability of habitats suitable for the development and reproduction of An. darlingi.

Ecology of Anopheles darlingi Root with respect to vector importance: a review

Anopheles darlingi is one of the most important malaria vectors in the Americas. In this era of new tools and strategies for malaria and vector control it is essential to have knowledge on the ecology and behavior of vectors in order to evaluate appropriateness and impact of control measures. This paper aims to provide information on the importance, ecology and behavior of An. darlingi. It reviews publications that addressed ecological and behavioral aspects that are important to understand the role and importance of An. darlingi in the transmission of malaria throughout its area of distribution. The results show that Anopheles darlingi is especially important for malaria transmission in the Amazon region. Although numerous studies exist, many aspects determining the vectorial capacity of An. darlingi, i.e. its relation to seasons and environmental conditions, its gonotrophic cycle and longevity, and its feeding behavior and biting preferences, are still unknown. The vector shows a high degree of variability in behavioral traits. This makes it difficult to predict the impact of ongoing changes in the environment on the mosquito populations. Recent studies indicate a good ability of An. darlingi to adapt to environments modified by human development. This allows the vector to establish populations in areas where it previously did not exist or had been controlled to date. The behavioral variability of the vector, its adaptability, and our limited knowledge of these impede the establishment of effective control strategies. Increasing our knowledge of An. darlingi is necessary.

Survivorship of Anopheles darlingi (Diptera: Culicidae) in relation with malaria incidence in the Brazilian Amazon

We performed a longitudinal study of adult survival of Anopheles darlingi, the most important vector in the Amazon, in a malarigenous frontier zone of Brazil. Survival rates were determined from both parous rates and multiparous dissections. Anopheles darlingi human biting rates, daily survival rates and expectation of life where higher in the dry season, as compared to the rainy season, and were correlated with malaria incidence. The biting density of mosquitoes that had survived long enough for completing at least one sporogonic cycle was related with the number of malaria cases by linear regression. Survival rates were the limiting factor explaining longitudinal variations in Plasmodium vivax malaria incidence and the association between adult mosquito survival and malaria was statistically significant by logistic regression (P<0.05). Survival rates were better correlated with malaria incidence than adult mosquito biting density. Mathematical modeling showed that P. falciparum and P. malariae were more vulnerable to changes in mosquito survival rates because of longer sporogonic cycle duration, as compared to P. vivax, which could account for the low prevalence of the former parasites observed in the study area. Population modeling also showed that the observed decreases in human biting rates in the wet season could be entirely explained by decreases in survival rates, suggesting that decreased breeding did not occur in the wet season, at the sites where adult mosquitoes were collected. For the first time in the literature, multivariate methods detected a statistically significant inverse relation (P<0.05) between the number of rainy days per month and daily survival rates, suggesting that rainfall may cause adult mortality.

Malaria vector species in Colombia: a review

Here we present a comprehensive review of the literature on the vectorial importance of the major Anopheles malaria vectors in Colombia. We provide basic information on the geographical distribution, altitudinal range, immature habitats, adult behaviour, feeding preferences and anthropophily, endophily and infectivity rates. We additionally review information on the life cycle, longevity and population fluctuation of Colombian Anopheles species. Emphasis was placed on the primary vectors that have been epidemiologically incriminated in malaria transmission: Anopheles darlingi, Anopheles albimanus and Anopheles nuneztovari. The role of a selection of local, regional or secondary vectors (e.g., Anopheles pseudopunctipennis and Anopheles neivai) is also discussed. We highlight the importance of combining biological, morphological and molecular data for the correct taxonomical determination of a given species, particularly for members of the species complexes. We likewise emphasise the importance of studying the bionomics of primary and secondary vectors along with an examination of the local conditions affecting the transmission of malaria. The presence and spread of the major vectors and the emergence of secondary species capable of transmitting human Plasmodia are of great interest. When selecting control measures, the anopheline diversity in the region must be considered. Variation in macroclimate conditions over a species' geographical range must be well understood and targeted to plan effective control measures based on the population dynamics of the local Anopheles species.

Population dynamics, structure and behavior of Anopheles darlingi in a rural settlement in the Amazon rainforest of Acre, Brazil

Background

Anopheles darlingi is the major vector of malaria in South America, and its behavior and distribution has epidemiological importance to biomedical research. In Brazil, An. darlingi is found in the northern area of the Amazon basin, where 99.5% of the disease is reported.

Methods

The study area, known as Ramal do Granada, is a rural settlement inside the Amazon basin in the state of Acre. Population variations and density have been analysed by species behaviour, and molecular analysis has been measured by ND4 mitochondrial gene sequencing.

Results

The results show higher density in collections near a recent settlement, suggesting that a high level of colonization decreases the vector presence. The biting activity showed higher activity at twilight and major numbers of mosquitos in the remaining hours of the night in months of high density. From a sample of 110 individual mosquitoes, 18 different haplotypes were presented with a diversity index of 0.895, which is higher than that found in other Anopheles studies.

Conclusions

An. darlingi depends on forested regions for their larval and adult survival. In months with higher population density, the presence of mosquitoes persisted in the second part of the night, increasing the vector capacity of the species. Despite the intra-population variation in the transition to rainy season, the seasonal distribution of haplotypes shows no change in the structure population of An. darlingi.

Assessment of routine malaria diagnosis in the Venezuelan Amazon

The quality of routine malaria diagnosis is a crucial topic of malaria control. The aim of this assessment was to monitor and evaluate the quality of routine malaria diagnosis in Amazonas (Venezuela) and to improve the quality control system. The traditional non-blinded quality control system was found to be overburdened with diagnostic samples. A modified sampling system with fewer samples to be tested was proposed. Expert microscopists blindly double-checked 1000 slides and 550 rapid diagnostic tests (RDT) (OptiMAL-IT) from health posts (HP). For Plasmodium vivax, HP microscopy and OptiMAL-IT showed sensitivies of 86% and 63%, respectively. For P. falciparum, HP microscopy and OptiMAL-IT showed sensitivities of 68% and 89%, respectively. Both methods lost accuracy when fewer parasites occurred in the sample. HP microscopists from different municipalities displayed significant differences in diagnostic quality. Overall, quality of routine malaria diagnosis in the Venezuelan Amazon is good but not optimal. The change from the traditional non-blinded quality control system to blinded cross-checking of a minimal selection of samples is - comparatively - a low cost intervention with possibly high impact on the quality of routine malaria diagnosis. The introduction of RDTs should be discussed carefully in order not to displace an existing network of HP microscopists.

Influence of climate and river level on the incidence of malaria in Cacao, French Guiana

BACKGROUND

The epidemiological profiles of vector-borne diseases, such as malaria, are strongly associated with environmental conditions. An understanding of the effect of the climate on the occurrence of malaria may provide indirect insight into the anopheles mosquito vectors endemic to a particular region. The association between meteorological and hydrographical factors and the occurrence of malaria was studied in a village in French Guiana during an epidemic caused essentially by Plasmodium vivax.

METHODS

A cohort of confirmed cases of P. vivax malaria occurring between 2002 and 2007 was studied to search for an association between the number of new infection episodes occurring each month, mean, maximum and minimum monthly temperatures, cumulative rainfall for the month and the mean monthly height of the river bordering the village, with the aid of time series. Cross-correlation analysis revealed that these meteorological factors had large effects on the number of episodes, over a study period of 12 months.

RESULTS

Climatic factors supporting the continuance of the epidemic were identified in the short-term (low minimum temperatures during the month), medium-term (low maximum temperatures two months before) and long-term (low maximum temperatures nine months before and high lowest level of the river 12 months before). Cross-correlation analysis showed that the effects of these factors were greatest at the beginning of the short rainy season.

CONCLUSION

The association between the river level and the number of malaria attacks provides clues to better understand the environment of malaria transmission and the ecological characteristics of the vectors in the region.

Genetic differences based on AFLP markers in the mosquito species Anopheles darlingi collected in versus near houses in the region of Porto Velho, RO, Brazil

Anopheles darlingi is the most important malaria vector in Central and South America. After a dramatic reduction of malaria cases in the whole Brazilian territory, with the lowest abundance being attained by 1970, the disease resurged in the Amazon region, where it is now a great public health concern. Consequently, better knowledge about vector species became urgent. We examined the genetic diversity and population structure of A. darlingi, sampled in four localities in the State of Rondônia, Brazil, using 139 amplified fragment length polymorphism marker loci. In each locality, samples were collected in two environments: a peri-domicile one (in the balconies of houses) and an extra-domicile environment (about 15 m from the house). Estimates of expected heterozygosity, Shannon diversity index and percentage of polymorphic loci showed medium to high values, with the samples from the areas closer to Porto Velho exhibiting the smallest values. There was evidence of small population differences, evaluated by F(st), genetic distance and analysis of molecular variance. Comparison between peri- and extra-domicile samples showed greater values of F(st) and genetic distance than between pairs of localities, indicating influence of environmental conditions on the genetics of populations.

The dominant Anopheles vectors of human malaria in the Americas: occurrence data, distribution maps and bionomic précis

BACKGROUND

An increasing knowledge of the global risk of malaria shows that the nations of the Americas have the lowest levels of Plasmodium falciparum and P. vivax endemicity worldwide, sustained, in part, by substantive integrated vector control. To help maintain and better target these efforts, knowledge of the contemporary distribution of each of the dominant vector species (DVS) of human malaria is needed, alongside a comprehensive understanding of the ecology and behaviour of each species.

RESULTS

A database of contemporary occurrence data for 41 of the DVS of human malaria was compiled from intensive searches of the formal and informal literature. The results for the nine DVS of the Americas are described in detail here. Nearly 6000 occurrence records were gathered from 25 countries in the region and were complemented by a synthesis of published expert opinion range maps, refined further by a technical advisory group of medical entomologists. A suite of environmental and climate variables of suspected relevance to anopheline ecology were also compiled from open access sources. These three sets of data were then combined to produce predictive species range maps using the Boosted Regression Tree method. The predicted geographic extent for each of the following species (or species complex*) are provided: Anopheles (Nyssorhynchus) albimanus Wiedemann, 1820, An. (Nys.) albitarsis*, An. (Nys.) aquasalis Curry, 1932, An. (Nys.) darlingi Root, 1926, An. (Anopheles) freeborni Aitken, 1939, An. (Nys.) marajoara Galvão & Damasceno, 1942, An. (Nys.) nuneztovari*, An. (Ano.) pseudopunctipennis* and An. (Ano.) quadrimaculatus Say, 1824. A bionomics review summarising ecology and behaviour relevant to the control of each of these species was also compiled.

CONCLUSIONS

The distribution maps and bionomics review should both be considered as a starting point in an ongoing process of (i) describing the distributions of these DVS (since the opportunistic sample of occurrence data assembled can be substantially improved) and (ii) documenting their contemporary bionomics (since intervention and control pressures can act to modify behavioural traits). This is the first in a series of three articles describing the distribution of the 41 global DVS worldwide. The remaining two publications will describe those vectors found in (i) Africa, Europe and the Middle East and (ii) in Asia. All geographic distribution maps are being made available in the public domain according to the open access principles of the Malaria Atlas Project.

Microgeographic genetic variation of the malaria vector Anopheles darlingi root (Diptera: Culicidae) from Cordoba and Antioquia, Colombia

Anopheles darlingi is an important vector of Plasmodium spp. in several malaria-endemic regions of Colombia. This study was conducted to test genetic variation of An. darlingi at a microgeographic scale (approximately 100 km) from localities in Córdoba and Antioquia states, in western Colombia, to better understand the potential contribution of population genetics to local malaria control programs. Microsatellite loci: nuclear white and cytochrome oxidase subunit I (COI) gene sequences were analyzed. The northern white gene lineage was exclusively distributed in Córdoba and Antioquia and shared COI haplotypes were highly represented in mosquitoes from both states. COI analyses showed these An. darlingi are genetically closer to Central American populations than southern South American populations. Overall microsatellites and COI analysis showed low to moderate genetic differentiation among populations in northwestern Colombia. Given the existence of high gene flow between An. darlingi populations of Córdoba and Antioquia, integrated vector control strategies could be developed in this region of Colombia.

Annual variations in the number of malaria cases related to two different patterns of Anopheles darlingi transmission potential in the Maroni area of French Guiana

Background

With an Annual Parasite Incidence (API) of 132.1, in the high and moderate risks zones, the Maroni area of French Guiana has the second highest malaria incidence of South-America after Guyana (API = 183.54) and far above Brazil (API = 28.25). Malaria transmission is occurring despite strong medical assistance and active vector control, based on general WHO recommendations. This situation is generated by two main factors that are the social and cultural characteristics of this border area, where several ethnic groups are living, and the lack of understanding of transmission dynamics of the main mosquito vector, Anopheles darlingi. In this context, entomological data collected in two villages belonging to two different ethnic groups of the French border of the Maroni River, were retrospectively analysed to find out how the mosquito bionomics are related to the malaria transmission patterns.

Methods

Data were provided by human landing catches of mosquitoes carried out each month for two years in two villages belonging to two ethnic groups, the Amerindians Wayanas and the Aloukous of African origin. The mosquitoes were sorted by species, sex, date, hour and place of collection and processed for Plasmodium sp. parasite detection. The data were compiled to provide the following variables: human biting rates (HBR), parity rates (PR), numbers of infective bites (IB), entomological inoculation rates (EIR) and numbers of infected mosquitoes surviving enough to transmit (IMT). Spatial and temporal differences of variables between locations and during the night were tested by the Kruskall-Wallis analysis of variance to find out significant variations.

Results

The populations of the main mosquito vector An. darlingi showed significant variations in the spatial and temporal HBR/person/night and HBR/person/hour, IB/person/month and IB/person/hour, and IMT/village/night and IMT/village/hour. In the village of Loca (Aloukous), the IMT peaked from June to August with a very low transmission during the other months. The risks were higher during the first part of the night and an EIR of 10 infective bites per person and per year was estimated. In the village of Twenke (Wayanas), high level of transmission was reported all year with small peaks in March and October. The risk was higher during the second part of the night and an EIR of 5 infective bites per person and per year was estimated.

Conclusion

For the first time in the past 40 years, the mosquito bionomics was related to the malaria transmission patterns in French Guiana. The peak of malaria cases reported from August to October in the Maroni region is concomitant with the significant peak of An. darlingi IMT, reported from the village of Loca where transmission is higher. However, the persistent number of cases reported all year long may also be related to the transmission in the Amerindian villages. The An. darlingi bionomics for these two close populations were found significantly different and may explain why a uniform vector control method is inadequate. Following these findings, malaria prevention measures adapted to the local conditions are needed. Finally, the question of the presence of An. darlingi sub-species is raised.

Malaria vectors in two indigenous reserves of the Brazilian Amazon

OBJECTIVE

To describe the composition, ecological and behavioral characteristics and infectivity of Anopheles species in indigenous reserves of the Amazon region.

METHODS

The study was performed in villages of the Nhamundá-Mapuera and Cuminapanema indigenous reserves, in the state of Pará, Northern Brazil, in 2002. A total of three two-week collections were conducted in each reserve, with the capture of adult and immature forms. Adult Anopheles specimens were captured using a Castro sucking tube with human landing trap in indoor and outdoor environments, from 6.00 pm to 9.00 pm and from 6.00 pm to 6.00 am, and subsequently assessed to verify parity and infectivity by plasmodiums using dissection and ELISA. Water collections near the villages were surveyed using 500 ml ladles, with 20 ladlefuls for each 10 m, covering the maximum extent of 200 m of perimeter around the breeding spot.

RESULTS

Adding up the collections from both reserves, a total of 8,668 females were captured. Anopheles darlingi was the most frequent species, with higher frequency around the homes. In the Mapuera reserve, blood feeding activity was concentrated between 8.00 pm and 12.00 am, while, in Cuminapanema, it remained high until 12.00 am, decreasing after this time and increasing again early in the morning. Of all the 6,350 An. darlingi females analyzed, 18 were infected with Plasmodium vivax VK247, VK210, P. falciparum and P. malariae. In addition, other 1,450 females of other species were analyzed, but none was found infected. An. nuneztovari and Chagasia bonnae were the most frequent species in the breeding spots of the Mapuera and Cuminapanema villages, respectively. Immature An. darlingi forms were not located in Mapuera and were captured in only one of the collections of the Cuminapanema reserve.

CONCLUSIONS

An. darlingi populations in the two reserves showed exophilic behavior and intense nocturnal activity. The occurrence of immature forms was little frequent and larval density was low. Vector behavioral characteristics were not favorable for the usual vector control activities.

A rapid malaria appraisal in the Venezuelan Amazon

Background

While the federal state of Amazonas bears the highest risk for malaria in Venezuela (2007: 68.4 cases/1000 inhabitants), little comprehensive information about the malaria situation is available from this area. The purpose of this rapid malaria appraisal (RMA) was to provide baseline data about malaria and malaria control in Amazonas.

Methods

The RMA methodology corresponds to a rapid health impact assessment (HIA) as described in the 1999 Gothenburg consensus. In conjunction with the actors of the malaria surveillance system, all useful data and information, which were accessible within a limited time-frame of five visits to Amazonas, were collected, analysed and interpreted.

Results

Mortality from malaria is low (< 1 in 10⁵) and slide positivity rates have stayed at the same level for the last two decades (15% ± 6% (SD)). Active case detection accounts for ca. 40% of slides taken. The coverage of the censured population with malaria notification points (NPs) has been achieved in recent years. The main parasite is Plasmodium vivax (84% of cases). The proportion of Plasmodium falciparum is on the decline, possibly driven by the introduction of cost-free artemisinin-based combination therapy (ACT) (1988: 33.4%; 2007: 15.4%). Monitoring and documentation is complete, systematic and consistent, but poorly digitalized. Malaria transmission displayed a visible lag behind rainfall in the capital municipality of Atures, but not in the other municipalities. In comparison to reference microscopy, quality of field microscopy and rapid diagnostic tests (RDTs) is suboptimal (kappa < 0.75). Hot spots of malaria risk were seen in some indigenous ethnic groups. Conflicting strategies in respect of training of community health workers (CHW) and the introduction of new diagnostic tools (RDTs) were observed.

Conclusion

Malaria control is possible, even in tropical rain forest areas, if the health system is working adequately. Interventions have to be carefully designed and the features of the particular local Latin American context considered.