Cow-baited tents are highly effective in sampling diverse Anopheles malaria vectors in Cambodia

Abstract

Background: The accurate monitoring and evaluation of malaria vectors requires efficient sampling. The objective of this study was to compare methods for sampling outdoor-biting Anopheles mosquitoes in Cambodia.

Methods: In the Cambodian provinces of Pursat, Preah Vihear, and Ratanakiri, six different mosquito trapping methods were evaluated: human landing collection (HLC), human-baited tent (HBT), cow-baited tent (CBT), CDC miniature light trap (LT), CDC miniature light trap baited with molasses and yeast (LT-M), and barrier fence (F) in a Latin square design during four or six consecutive nights at the height of the malaria transmission season.

Results: Using all traps, a total of 507, 1175, and 615 anophelines were collected in Pursat, Preah Vihear, and Ratanakiri, respectively. CBTs captured 10- to 20-fold more anophelines per night than the other five sampling methods. All 2297 Anopheles mosquitoes were morphologically identified and molecularly typed using standard morphological keys and sequencing the rDNA ITS2 region to distinguish cryptic species, respectively. Overall, an extremely diverse set of 27 known Anopheles species was sampled. CBTs captured the same molecular species that HLCs and the other four traps did, as well as additional species. Nine specimens representing five Anopheles species (Anopheles hyrcanus, Anopheles barbirostris sensu stricto, Anopheles barbirostris clade III, Anopheles nivipes, and Anopheles peditaeniatus) were infected with Plasmodium falciparum and were exclusively captured in CBTs.

Conclusions: These data indicate that cow-baited tents are highly effective in sampling diverse Anopheles malaria vectors in Cambodia. This sampling method captured high numbers of anophelines with limited sampling effort and greatly reduced human exposure to mosquito bites compared to the gold-standard human landing collection.

Keywords: Anopheles; Cambodia; Malaria; Outdoor transmission; Trap; Vector.

Fig. 1

Comparison of total hourly collection of the five most abundant Anopheles species sampled in three Cambodian provinces. a Pursat, b Preah Vihear, and c Ratanakiri. The vast majority (90 %) of anophelines were captured in cow-baited tents

Fig. 2

Number of anophelines captured per night using six collection methods in three Cambodian provinces. Each dot represents the total number of anophelines collected in a single night in Pursat, Preah Vihear, and Ratanakiri provinces in Cambodia. Horizontal line and error bars indicate mean and SD. The trapping methods included: CBT cow-baited tent, HBT human-baited tent, HLC human landing collection, F-I (fence facing village), F-O (fence facing away from village), F (both sides of fence combined—Ratanakiri only), LT (CDC light trap), LT-M (CDC light trap baited with molasses and yeast). The asterisks represent comparisons of trap effects on total anopheline catch by ANOVA and Tukey’s multiple comparison test where *p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001, and ****p ≤ 0.0001. NB: this figure includes all anophelines collected, not all of which were molecularly analysed for species identification and Plasmodium infection