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

Abstract

BackgroundThe 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.MethodsMalaria 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.ResultsThere 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.ConclusionsLight 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.

Comparison of two adult mosquito sampling methods with human landing catches in south-central Ethiopia

“…In contrast to these results, several studies [2, 4, 11, 35, 36] showed higher sampling efficiency of LTC compared with HLC for different Anopheles species including An. arabiensis .…”

Entomologic Inoculation Rates of Anopheles arabiensis in Southwestern Ethiopia

“…However, CDC light traps failed to determine the human-biting rate of An. gambiae s.s. on Bioko Island, Equatorial Guinea 29. In Tanzania, approximately two-thirds of the human-biting An.…”

Design and Testing of a Novel, Protective Human-Baited Tent Trap for the Collection of Anthropophilic Disease Vectors

“…Several investigators have observed no differences in Anopheles capture rates if long-lasting permethrin-treated bed nets are used in LTC rather than untreated bed nets, thus improving the safety for the collector (Magbity et al 2002, Fornadel et al 2010, Govella et al 2011). In some studies, LTC accurately reflected the species composition, capture rates, or vector bionomics of the HLC (Mathenge et al 2004, Govella et al 2009), whereas in other studies, consistent associations failed (Overgaard et al 2012). When LTC accurately reflects HLC, a conversion factor is typically needed to adjust the raw numbers because the LTC tends to underestimate the number of mosquitoes captured by HLC (Overgaard et al 2012).…”

“…In some studies, LTC accurately reflected the species composition, capture rates, or vector bionomics of the HLC (Mathenge et al 2004, Govella et al 2009), whereas in other studies, consistent associations failed (Overgaard et al 2012). When LTC accurately reflects HLC, a conversion factor is typically needed to adjust the raw numbers because the LTC tends to underestimate the number of mosquitoes captured by HLC (Overgaard et al 2012). …”

“…Mutero et al used a homemade updraft trap suspended over a bed net to successfully capture host-seeking African malaria vectors (Mutero and Birley 1987). Many investigators now use a similar design, but for consistency, most use commercially purchased Center for Disease Control and Prevention (CDC) mini-light traps (LTC) hung next to the feet of a human resting under a bed net (Lines et al 1991, Ndiath et al 2011, Overgaard et al 2012). Several investigators have observed no differences in Anopheles capture rates if long-lasting permethrin-treated bed nets are used in LTC rather than untreated bed nets, thus improving the safety for the collector (Magbity et al 2002, Fornadel et al 2010, Govella et al 2011).…”