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 Americans 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.) albitaris*, An. (Nys.) aquasalis Curry, 1932, An. (Nys.) darlingi Root, 1926, An. (Anopheles) freeborni Aitken, 1939, An. (Nys.) marajoara Galvāo & Damasceno, 1942, An. (Nys.) nuneztovari*, An. (Ano.) pseudopunctipennis* and An. (Ano.) quadrimaculatus Say, 1824. A bionomics review summarising ecology and behaviour relevant to the 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 samples 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

A global map of dominant malaria vectors

Background: Global maps, in particular those based on vector distributions, have long been used to help visualise the global extent of malaria. Few, however, have been created with the support of a comprehensive and extensive evidence-based approach.\ud Methods: Here we describe the generation of a global map of the dominant vector species (DVS) of malaria that makes use of predicted distribution maps for individual species or species complexes.\ud Results: Our global map highlights the spatial variability in the complexity of the vector situation. In Africa, An. gambiae, An. arabiensis and An. funestus are co-dominant across much of the continent, whereas in the Asian- Pacific region there is a highly complex situation with multi-species coexistence and variable species dominance.\ud Conclusions: The competence of the mapping methodology to accurately portray DVS distributions is discussed. The comprehensive and contemporary database of species-specific spatial occurrence (currently available on request) will be made directly available via the Malaria Atlas Project (MAP) website from early 2012

Developing Global Maps of the Dominant Anopheles Vectors of Human Malaria

Simon Hay and colleagues describe how the Malaria Atlas Project has collated anopheline occurrence data to map the geographic distributions of the dominant mosquito vectors of human malaria

Vector biology and malaria transmission in western Venezuela

The status of all anopheline species reported to occur in western Venezuela is reviewed. A longitudinal study was conducted in three villages in western Venezuela to assess the malaria risk factors determined by the abundance, parous rate, biting activity, sporozoite rate and human blood index of the various potential vector species in relation to weather and human habits. The main method of mosquito sampling was on human baits; three other methods tested did not prove to be effective substitutes. The collections yielded 14 anopheline species, the most abundant being those belonging to the subgenus Nyssorhynchus. Because species identification of adult females with available keys proved to be difficult, linked rearings were undertaken. An. nuneztovari, comprising over 70% of the total anophelines collected, was the most abundant species, followed by An. triannulatus, An. albitarsis s. l. and An. oswaldoi. The anopheline populations showed fluctuations which correlated positively with rainfall and humidity. The four most abundant species showed different diel patterns of biting. The diel peak for An. nuneztovari was close to midnight indoors and outdoors, for An. triannulatus between 1900 and 2000 hours outdoors, for An. albitarsis mainly before midnight indoors and outdoors and for An. oswaldoi outdoors at 1900 hrs, there being an additional smaller peak indoors at midnight. Most of the human population use bed nets, go to bed before 2200 hrs and wake up before 0700 hrs: they are therefore most exposed to the bites of those species that bite early in the night outdoors. All anopheline species in the study area are exophilic. Some anophelines were collected resting on vegetation around houses between 0600 and 0800 hrs but very few An. nuneztovari were found there. The source of blood meals in resting mosquitoes was determined by the ELISA technique. The human blood index for the different species collected showed variations among villages that could not be explained by variation in the ratio of humans to cows in each village. 2 Over 61,000 anophelines were assayed by ELISA to detect P. vivax circumsporozoite protein. The six specimens confirmed as positive belonged to three species: nuneztovari, albitarsis s. l. and oswaldoi. The estimated overall sporozoite rate was 0.0098% (95% confidence limits 0.0036 to 0.0214%). Multiplying this rate by the mean number of bites on the catchers suggests a sporozoite inoculation rate of 10.5 positive bites per person per year. Recommendations for possible improvements in malaria vector control in this area are made taking into account the endophagic and exophilic behaviour of the incriminated vectors, their diel patterns of biting and some aspects of the behaviour of the human population revealed by questionnaires

First report of Anopheles (Anopheles) calderoni (Diptera: Culicidae) in Venezuela

Se reporta por primera vez en Venezuela la presencia de Anopheles (Anopheles) calderoni Wilkerson 1991 con base en hembras colectadas en los estados Barinas y Táchira e identificadas previamente como A. punctimacula Dyar y Knab, 1906

Evaluación del poder residual del insecticida deltametrina en telas de mosquiteros

Se realizaron bioensayos con mosquitos Aedes aegypti (Linnaeus) (Diptera: Culicidae) cepa Rock para evaluar el poder residual del insecticida piretroide deltametrina 2,5% C.E. en telas blancas y verdes de poliéster y nylon, tratados en forma manual e industrial (PermaNetTM). Los bioensayos consistieron en exponer diez mosquitos durante tres minutos a cada una de las telas tratadas por triplicado y sus respectivos controles. Se registró el número de mosquitos caídos a los diez minutos (efecto knockdown ) y la mortalidad a las 24 horas. Luego de cada bioensayo, se procedía a lavar las telas a mano con jabón y se dejaban secar a la sombra. Para cada prueba, se lavaron las telas hasta observar mortalidades iguales o menores de 50%. En general se observó que a medida que aumenta el número de lavadas se reduce el poder residual del insecticida. En las telas PermaNetTM, tratadas en forma industrial, se observó 70% de mortalidad a las 24 horas luego de siete lavadas, requiriéndose la re-impregnación luego de ocho lavadas (36,6% de mortalidad). En telas tratadas manualmente el poder residual se mantiene hasta la cuarta o quinta lavada. El mayor poder residual de la deltametrina observado en telas tratadas en forma industrial (PermaNetTM) representa una ventaja que debe ser considerada cuando se plantee el uso de telas tratadas (mosquiteros/cortinas) con insecticida como medida alternativa o complementaria en programas de control de vectores