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01.12.2012 | Research | Ausgabe 1/2012 Open Access

Malaria Journal 1/2012

Light traps fail to estimate reliable malaria mosquito biting rates on Bioko Island, Equatorial Guinea

Zeitschrift:
Malaria Journal > Ausgabe 1/2012
Autoren:
Hans J Overgaard, Solve Sæbø, Michael R Reddy, Vamsi P Reddy, Simon Abaga, Abrahan Matias, Michel A Slotman
Wichtige Hinweise

Electronic supplementary material

The online version of this article (doi:10.​1186/​1475-2875-11-56) contains supplementary material, which is available to authorized users.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

HJO conceived, supervised, and planned the study, supervised, performed field collections and wrote the first draft manuscript. SS performed the Bayesian statistical analysis, wrote parts of the statistical methods and result sections, and provided general statistical advice. MRR participated in the study design and provided editorial input. VPR conducted molecular analyses. SA participated in the study design, supervised and participated in field collections, and provided editorial input. AM participated in study design, participated in field collections, and provided editorial input. MAS participated in study design, supervised the molecular analysis, and contributed to manuscript preparation. All authors read and approved the final manuscript.

Abstract

Background

The human biting rate (HBR), an important parameter for assessing malaria transmission and evaluating vector control interventions, is commonly estimated by human landing collections (HLC). Although intense efforts have been made to find alternative non-exposure mosquito collection methods, HLC remains the standard for providing reliable and consistent HBRs. The aim of this study was to assess the relationship between human landing and light trap collections (LTC), in an attempt to estimate operationally feasible conversion factors between the two. The study was conducted as part of the operational research component of the Bioko Island Malaria Control Project (BIMCP), Equatorial Guinea.

Methods

Malaria mosquitoes were collected indoors and outdoors by HLCs and LTCs in three villages on Bioko Island, Equatorial Guinea during five bimonthly collections in 2009. Indoor light traps were suspended adjacent to occupied long-lasting, insecticide-treated bed nets. Outdoor light traps were placed close to the outer wall under the roof of the collection house. Collected specimens were subjected to DNA extraction and diagnostic PCR to identify species within the Anopheles gambiae complex. Data were analysed by simple regression of log-transformed values and by Bayesian regression analysis.

Results

There was a poor correlation between the two collection methods. Results varied by location, venue, month, house, but also by the statistical method used. The more robust Bayesian analyses indicated non-linear relationships and relative sampling efficiencies being density dependent for the indoor collections, implying that straight-forward and simple conversion factors could not be calculated for any of the locations. Outdoor LTC:HLC relationships were weak, but could be estimated at 0.10 and 0.07 for each of two locations.

Conclusions

Light trap collections in combination with bed nets are not recommended as a reliable method to assess human biting rates on Bioko Island. Different statistical analyses methods give variable and inconsistent results. Substantial variation in collection methods prevents the determination of reliable and operationally feasible conversion factors for both indoor and outdoor data. Until improved mosquito collection methods are developed that can provide reliable and unbiased HBR estimates, HLCs should continue to serve as the reference method for HBR estimation.
Zusatzmaterial
Additional file 1: Number of Anopheline mosquitoes and proportion blood-fed collected on Bioko Island, Equatorial Guinea, 2009. (XLSX 119 KB)
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Additional file 2: Anopheles gambiae s.l. mosquitoes identified to species and molecular form from mosquito collections on Bioko Island, Equatorial Guinea, 2009. (XLSX 221 KB)
12936_2011_2104_MOESM2_ESM.XLSX
Authors’ original file for figure 1
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Authors’ original file for figure 2
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Authors’ original file for figure 3
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Authors’ original file for figure 4
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Authors’ original file for figure 5
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