Estimating absolute indoor density of Aedes aegypti using removal sampling

Abstract

Background Quantification of adult Aedes aegypti abundance indoors has relied on estimates of relative density (e.g. number of adults per unit of sampling or time), most commonly using traps or timed collections using aspirators. The lack of estimates of the sensitivity of collections and lack of a numerical association between relative and the absolute density of adult Ae. aegypti represent a significant gap in vector surveillance. Here, we describe the use of sequential removal sampling to estimate absolute numbers of indoor resting Ae. aegypti and to calculate calibration coefficients for timed Prokopack aspirator collections in the city of Merida, Yucatan State, Mexico. The study was performed in 200 houses that were selected based on recent occurrence of Aedes -borne viral illness in residents. Removal sampling occurred in 10-minute sampling rounds performed sequentially until no Ae. aegypti adult was collected for 3 hours or over 2 consecutive 10-minute periods. Results A total of 3439 Ae. aegypti were collected. The sensitivity of detection of positive houses in the first sampling round was 82.5% for any adult Ae. aegypti , 78.5% for females, 75.5% for males and 73.3% for blood-fed females. The total number of Ae. aegypti per house was on average ~5 times higher than numbers collected for the first sampling round. There was a positive linear relationship between the relative density of Ae. aegypti collected during the first 10-min round and the absolute density for all adult metrics. Coefficients from the linear regression were used to calibrate numbers from 10-min collections into estimates of absolute indoor Ae. aegypti density for all adults, females and males. Conclusions Exhaustive removal sampling represents a promising method for quantification of absolute indoor Ae. aegypti density, leading to improved entomological estimates of mosquito distribution, a key measure in the assessments of the risk pathogen transmission, disease modeling and the evaluation of vector control interventions.

Measuring mosquito control: adult-mosquito catches vs egg-trap data as endpoints of a cluster-randomized controlled trial of mosquito-disseminated pyriproxyfen

“…5 ). Whatever the actual underlying mechanism(s), our results suggest that the widely used egg-trap-based monitoring may measure poorly the impact of Aedes control; even if more costly, direct monitoring of the adult mosquito population is likely to provide a much more realistic and informative picture of intervention effects [ 5 , 37 – 40 , 62 ]. The fact that we found very little among-collector variation in mosquito-aspiration catches lends further support to this idea.…”

“…Here, we address this gap by presenting the results of a neighborhood-scale, parallel, two-arm cluster-randomized controlled trial (CRCT) of MD-PPF. In particular, we set to measure the impact of MD-PPF on local Aedes and Culex populations through both (i) active aspiration of adult mosquitoes, which directly measures adult-mosquito density [ 37 – 40 ], and (ii) egg-trap-based monitoring of female Aedes presence (proportion of positive egg-traps) and possibly abundance (number of eggs per egg-trap) [ 37 , 41 , 42 ]. Using a CRCT design, 16 months of field data, and a rigorous statistical-modeling strategy, we show that MD-PPF can significantly reduce adult-mosquito densities, yet Aedes egg-trap-based metrics may fail to detect this reduction.…”

Modeling Temperature Effects on Population Density of the Dengue Mosquito Aedes aegypti

“…For instance, a location with a high vector density increases the chance for contact with the host, which increases disease risk and facilitates disease spread [26,27]. However, measuring mosquito abundance in the field can be challenging, and the role climate factors play in the global distribution and dynamics of mosquitoes including A. aegypti remains unclear [28,29]. Instead of relying exclusively on measurements, mathematical models could potentially help bridge the gap between what we know about vector biology and the dynamics of vector populations.…”

Natural arbovirus infection rate and detectability of indoor female Aedes aegypti from Mérida, Yucatán, Mexico

“…Furthermore, the lack of accurate entomological correlates of ABV risk [ 2 , 16 , 17 ], is affected by multiple sources of bias including the difficulty of detecting and accurately quantifying immature or adult Ae . aegypti density [ 18 ], the exposure of people to mosquitoes in residences other than their homes [ 19 , 20 ], the variable level of susceptibility in the human population against each virus [ 21 ], or the limited predictive power of entomological indices for informing vector control [ 22 ].…”

“…aegypti collection [ 37 , 39 ]. Applying sequential removal sampling using Prokopack aspirators [ 18 , 39 ] the absolute density of Ae . aegypti was found to be up to five times bigger than previously estimated implementing the standard 10-minute collection period per household.…”