Abstract
BackgroundAn often confounding facet of the dynamics of malaria vectors is the aquatic larval habitat availability and suitable conditions under which they can thrive. Here, we investigated the impact of environmental factors on the temporal and spatial distribution of larval habitats of Anopheles arabiensis in different locations on La Reunion Island.MethodsA retrospective examination was made from archival data which provided the complete enumeration of An. arabiensis breeding habitats in three distinct geographic zones - extending North-east, West and South of the island over 14 years, from January 1996 to December 2009. Data on the occurrence and the number of active larval habitats at each of a total of 4376 adjacent ellipsoid grid cells (216,506 square meters each) were used (1) to provide the geographic extent of breeding site availability from year to year and (2) to analyze associations with prevailing environmental factors, habitat types, and locations.ResultsAnopheles arabiensis utilized a spectrum of man-made and natural aquatic habitats, most of which were concentrated primarily in the rock pools located in ravines and river fringes, and also in the large littoral marshes and within the irrigated agricultural zones. The numbers of breeding site per sampling grid differed significantly in different parts of the island. In contrast to an originally more widespread distribution across the island in the 1950s, detailed geographic analyses of the data obtained in the period extending from 1996-2009 showed an intriguing clustered distribution of active breeding sites in three discontinuous geographic zones, in which aquatic habitats availability fluctuates with the season and year. Seasonality in the prevalence of anopheles breeding sites suggests significant responsiveness to climatic factors.ConclusionsThe observed retreat of An. arabiensis distribution range to lower altitudinal zones (< 400 m) and the upward shift in the most remote littoral areas in the northeast and southwest regions suggest the possible influence of biogeographic factors, changes in land use and control operations. The results of this study would allow for a more rational implementation of control strategies across the island.
Highlights
An often confounding facet of the dynamics of malaria vectors is the aquatic larval habitat availability and suitable conditions under which they can thrive
The objective of this study was to define the habitat ranges of An. arabiensis in La Reunion Island, and to determine whether the presence or absence of their larval habitats could be predicted based upon environmental variables at three distinctive regions of the island
It is characterized by a hot rainy season which usually lasts from November to April and a dry winter which begins in May and ends in October
Summary
An often confounding facet of the dynamics of malaria vectors is the aquatic larval habitat availability and suitable conditions under which they can thrive. A few local cases of Plasmodium falciparum malaria have been reported three times in 2000, 2005 and 2006 (The French Ministry of Health - ARS-Indian Ocean, unpublished data) This attests to the vulnerability of the island with regard to a malaria transmission risk. Such threat of the resurgence of malaria (i.e. the presence of malaria vectors and the regular introduction of infected patients) in this tropical island is a major public-health issue [6]. This calls for an intensive planning effort to prepare for the possible re-emergence of malaria, but for a long-term comprehensive approach to preventing mosquito-borne diseases. No previous studies allow direct inferences about the risk of re-emergence of malaria in La Reunion
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