Man biting rate seasonal variation of malaria vectors in Roraima, Brazil

Abstract

Malaria control has been directed towards regional actions where more detailed knowledge of local determinants of transmission is of primary importance. This is a short report on range distribution and biting indices forThe most important local vector species have been determined to be An. darlingi Root and An. albitarsis sensu lato. As we have not taxonomically determined the species in the albitarsis complex ourselves, hereinafter the species will be simply referred as An. albitarsis. Nonetheless, previous studies determined the An. albitarsis population in Jardim das Copaíbas, our study area, as An. albitarsis species E (Póvoa et al. 2006). Studies using entomological inoculation rates and biting indices have implicated An. darlingi and An. albitarsis as the most important vectors in the area (Silva-Vasconcelos et al. 2002, Póvoa et al. 2006.In this communication we describe seasonal variations in the biting rate of two main local malaria vectors in Jardim das Copaíbas a riverside settlement in the Northern Amazon Basin during one year. An equation describing the distribution range of An. darlingi during the rainy season was also determined.The study area Jardim das Copaíbas is a rural settlement (02°45'28''N, 60°42' 18''W) by the Branco River 5 km south of Boa Vista, the capital of the state of Roraima (Fig. 1B). Jardim das Copaíbas can be characterized as a savanna/alluvial forest landscape area. This is because the settlement is located in a savanna in close contact (~ 100 m) to a dense alluvial rainforest that delineates the Branco River. The area has a long rainy season (April-November), a short dry season (DecemberMarch), in which the Branco River water levels increase (Póvoa et al. 2006, Fig. 2). During the rainy season, the alluvial forest becomes partly flooded. Average yearly rainfall is 1100-1400 mm/year and temperatures are permanently high (daily average 27.8ºC) with little yearlong variation. Relative humidity is also high (daily average 73.8%) and varies little over the year (Furley 1994).In . Rainfall data and river water levels were registered (Fig. 2).The 1n + 1 transformed numbers of mosquitoes captured during peak biting activity (the first 4 h after sunset) were used during the rainy season for deriving an exponential regression function for An. darlingi distribution range. Estimations of the percentages of the adult An. darlingi population that could reach over specified distances were given by the expression: y = 4.435 exp(x*-0.003) (p < 0.001, r = 0.98) where x is the distance from the larval habitat and y the percentage of the adult mosquitoes. Since An. albitarsis also has larval habitat dispersed in the open savanna fields, a distribution range function could not be derived from the data collected. It was not possible to determine all larval habitats for each species. The transect represents the closest distance a certain mosquito would have to fly to reach the capture stations.

Links between Climate, Malaria, and Wetlands in the Amazon Basin

“…Studies have proposed that fl ooding created new pools of water suitable for mosquito larvae as the water levels slowly receded from alluvial forests along the Rio Branco River in Roraima and the Maroni River on the frontiers of Suriname and French Guiana (6,15). Our results suggest that monthly precipitation along the Amazon Basin can have both strong positive and negative associations with malaria incidence.…”

“…Short longitudinal studies show that human-landing catches of An. darlingi, which breeds along the edges and in debris of clear, partially sunlit pools, are closely associated with local malaria rates (5,6). These observations establish that biting rates are elevated in regions of elevated malaria risk.…”

Adaptative processes, control measures, genetic background, and resilience of malaria vectors and environmental changes in the Amazon region

“…The distributions of A. darlingi and A. albitarsis therefore fluctuate according to these variations in river levels under natural conditions. These results demonstrate significant positive correlations between cases of malaria and temperature, precipitation, and water levels (Barros & Honório, 2007). Similarly, Wolfarth et al (2013) noted that increases in water levels in recent years also reflect the malaria transmission cycle.…”

An ecoregional classification for the state of Roraima, Brazil: the importance of landscape in malaria biology

“…Alluvial forest corridors can be up to 500 m wide in low-elevation areas, are subject to seasonal flooding, and may support significant mosquito vector populations. The link between important malaria vectors and alluvial forest is well-known (Amaral & Penido 1947, Andrade & Leal 1960, Rubio-Palis & Zimmerman 1997, Barros & Honório 2007.All vector species except An. peryassui likely occur in this region.…”

“…Our 8-unit ecoregion classification, although close to that of Olson, further divides the Guianan savannah into 2 ecoregions (steppe and savannah), and classifies alluvial forests as a separate ecoregion; however, we do not recognize Negro-Branco River moist forest as separate, instead combining it with other lowland forests (ecoregion IV). It has been suggested that alluvial forests play important roles in malaria transmission (Barros & Honório 2007), as they are subject to seasonal flooding in the late rainy season, creating suitable breeding habitats for mosquitoes. We observed patches of specific subformations within the 8-unit ecoregion divisions that, excepting the alluvial forests, were not considered in this regional scale analysis and are nested within the 8 level-II ecoregions; at least 25 level-III ecoregions could be recognized (not shown).…”