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Spatial variability in the density, distribution and vectorial capacity of anopheline species in a high transmission village (Equatorial Guinea)

Cano J, Descalzo MA, Moreno M, Chen Z, Nzambo S, Bobuakasi L, Buatiche JN, Ondo M, Micha F, Benito A - Malar. J. (2006)

Bottom Line: The highest SI was found in A. carnevalei (24%), even though the HBR was the lowest for this species.A significant association was found between the distance from the dwellings to the closest water point (River Ntem or secondary streams) and the total HBR.A clear association has been observed between the distance to potential breeding sites and the variability in the anopheline density, while the other parameters measured do not seem to condition this spatial variability.

Affiliation: Centro Nacional de Medicina Tropical, Instituto de Salud Carlos III, C/Sinesio Delgado 6, Madrid, Spain. jcano@isciii.es

ABSTRACT

Background: Malaria transmission varies from one country to another and there are also local differences in time and space. An important variable when explaining the variability in transmission is the breeding behaviour of the different vector species and the availability of breeding sites. The aim of this study was to determine the geographical variability of certain entomological parameters: human biting rate (HBR), sporozoitic index (SI) for Plasmodium falciparum and entomological inoculation rate (EIR).

Methods: The study was carried out in a small village in the mainland region of Equatorial Guinea. Adult mosquitoes were collected by CDC light traps. Polymerase Chain Reaction was employed to identify the species within the Anopheles gambiae complex and to detect P. falciparum sporozoites. The geographical position of all the dwellings in the village were taken using a global positioning system receiver unit. Data relating to the dwelling, occupants, use of bednets and the mosquitoes collection data were used to generate a geographical information system (GIS). This GIS allowed the minimum distance of the dwellings to the closest water point (potential breeding sites) to be determined.

Results: A total of 1,173 anophelines were caught: 279 A. gambiae s.l. (217 A. gambiae s.s. and one Anopheles melas), 777 Anopheles moucheti and 117 Anopheles carnevalei. A. moucheti proved to be the main vector species and was responsible for 52.38 [95% IC: 33.7-71] night infective bites during this period. The highest SI was found in A. carnevalei (24%), even though the HBR was the lowest for this species. A significant association was found between the distance from the dwellings to the closest water point (River Ntem or secondary streams) and the total HBR.

Conclusion: A clear association has been observed between the distance to potential breeding sites and the variability in the anopheline density, while the other parameters measured do not seem to condition this spatial variability. The application of GIS to the study of vector-transmitted diseases considerably improves the management of the information obtained from field surveys and facilitates the study of the distribution patterns of the vector species.

Map of the mainland region of the Equatorial Guinea and location of the Yengüe village.
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Figure 1: Map of the mainland region of the Equatorial Guinea and location of the Yengüe village.

Mentions: Yengüe village (N 02° 13,392' E 009° 52,716') is located in the mainland region of Equatorial Guinea, in the Rio Campo municipality, in the frontier region with Cameroon (see Figure 1). The village is made up of three scattered units: Yengüe, Ncoho Mekah and Bilan. The village has a total of 37 dwellings, most of which are built out of wood with zinc roofs and earth floors.

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Spatial variability in the density, distribution and vectorial capacity of anopheline species in a high transmission village (Equatorial Guinea)

Cano J, Descalzo MA, Moreno M, Chen Z, Nzambo S, Bobuakasi L, Buatiche JN, Ondo M, Micha F, Benito A - Malar. J. (2006)

Map of the mainland region of the Equatorial Guinea and location of the Yengüe village.
© Copyright Policy
Figure 1: Map of the mainland region of the Equatorial Guinea and location of the Yengüe village.
Mentions: Yengüe village (N 02° 13,392' E 009° 52,716') is located in the mainland region of Equatorial Guinea, in the Rio Campo municipality, in the frontier region with Cameroon (see Figure 1). The village is made up of three scattered units: Yengüe, Ncoho Mekah and Bilan. The village has a total of 37 dwellings, most of which are built out of wood with zinc roofs and earth floors.

Bottom Line: The highest SI was found in A. carnevalei (24%), even though the HBR was the lowest for this species.A significant association was found between the distance from the dwellings to the closest water point (River Ntem or secondary streams) and the total HBR.A clear association has been observed between the distance to potential breeding sites and the variability in the anopheline density, while the other parameters measured do not seem to condition this spatial variability.

Affiliation: Centro Nacional de Medicina Tropical, Instituto de Salud Carlos III, C/Sinesio Delgado 6, Madrid, Spain. jcano@isciii.es

ABSTRACT

Background:

Background: Malaria transmission varies from one country to another and there are also local differences in time and space. An important variable when explaining the variability in transmission is the breeding behaviour of the different vector species and the availability of breeding sites. The aim of this study was to determine the geographical variability of certain entomological parameters: human biting rate (HBR), sporozoitic index (SI) for Plasmodium falciparum and entomological inoculation rate (EIR).

Methods: The study was carried out in a small village in the mainland region of Equatorial Guinea. Adult mosquitoes were collected by CDC light traps. Polymerase Chain Reaction was employed to identify the species within the Anopheles gambiae complex and to detect P. falciparum sporozoites. The geographical position of all the dwellings in the village were taken using a global positioning system receiver unit. Data relating to the dwelling, occupants, use of bednets and the mosquitoes collection data were used to generate a geographical information system (GIS). This GIS allowed the minimum distance of the dwellings to the closest water point (potential breeding sites) to be determined.

Results: A total of 1,173 anophelines were caught: 279 A. gambiae s.l. (217 A. gambiae s.s. and one Anopheles melas), 777 Anopheles moucheti and 117 Anopheles carnevalei. A. moucheti proved to be the main vector species and was responsible for 52.38 [95% IC: 33.7-71] night infective bites during this period. The highest SI was found in A. carnevalei (24%), even though the HBR was the lowest for this species. A significant association was found between the distance from the dwellings to the closest water point (River Ntem or secondary streams) and the total HBR.

Conclusion: A clear association has been observed between the distance to potential breeding sites and the variability in the anopheline density, while the other parameters measured do not seem to condition this spatial variability. The application of GIS to the study of vector-transmitted diseases considerably improves the management of the information obtained from field surveys and facilitates the study of the distribution patterns of the vector species.

View Similar Images In: Results  - Collection
View Article: Pubmed Central - HTML -  PubMed
Show All Figures - Show MeSH
getmorefigures.php?pmc=1435759&rFormat=json&query=null&req=5