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BACKGROUND: The mosquito landing rate measured by human landing catches (HLC) is the conventional endpoint used to evaluate the impact of vector control interventions on human-vector exposure. Non-exposure based alternatives to the HLC are desirable to minimize the risk of accidental mosquito bites. One such alternative is the human-baited double net trap (HDN), but the estimated personal protection of interventions using the HDN has not been compared to the efficacy estimated using HLC. This semi-field study in Sai Yok District, Kanchanaburi Province, Thailand, evaluates the performance of the HLC and the HDN for estimating the effect on Anopheles minimus landing rates of two intervention types characterized by contrasting modes of action, a volatile pyrethroid spatial repellent (VSPR) and insecticide-treated clothing (ITC). METHODS: Two experiments to evaluate the protective efficacy of (1) a VPSR and (2) ITC, were performed. A block randomized cross-over design over 32 nights was carried out with both the HLC or HDN. Eight replicates per combination of collection method and intervention or control arm were conducted. For each replicate, 100 An. minimus were released and were collected for 6 h. The odds ratio (OR) of the released An. minimus mosquitoes landing in the intervention compared to the control arm was estimated using logistic regression, including collection method, treatment, and experimental day as fixed effects. RESULTS: For the VPSR, the protective efficacy was similar for the two methods: 99.3%, 95% CI (99.5-99.0) when measured by HLC, and 100% (100, Inf) when measured by HDN where no mosquitoes were caught (interaction test p = 0.99). For the ITC, the protective efficacy was 70% (60-77%) measured by HLC but there was no evidence of protection when measured by HDN [4% increase (15-27%)] (interaction test p < 0.001). CONCLUSIONS: Interactions between mosquitoes, bite prevention tools and the sampling method may impact the estimated intervention protective efficacy. Consequently, the sampling method must be considered when evaluating these interventions. The HDN is a valid alternative trapping method (relative to the HLC) for evaluating the impact of bite prevention methods that affect mosquito behaviour at a distance (e.g. VPSR), but not for interventions that operate through tarsal contact (e.g., ITC).

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The performances of the human-baited double net trap (HDNT) and the human-baited host decoy trap (HDT) methods were compared against the outdoor human landing catch (OHLC) method in Thailand and Vietnam. Two study sites were selected in each country: a rural village and a nearby forest setting. The three outdoor trap methods were rotated nightly between three set trapping positions, in a pre-assigned Latin square design. Volunteers were rotated following the trap rotation to avoid bias. The greatest number of adult mosquitoes was collected from the forest sites in both countries, showing Anopheles minimus (s.s.) Theobald (96.54%) and Anopheles dirus (s.s.) Peyton & Harrison (25.71%) as the primary malaria vectors in Thailand and Vietnam, respectively. At the Thai forest site, OHLC collected significantly more anopheline mosquitoes per trap night than HDNT and HDT, with mean ± standard error values of 14.17 ± 4.42, 4.83 ± 1.56, and 4.44 ± 1.45, respectively, whilst HDNT and HDT were significantly less productive at 0.34 times and 0.31 times, respectively, than OHLC in capturing anopheline mosquitoes. However, there were no significant differences among the three methods of trapping malaria vectors for the village site. At the Vietnamese forest site, HDNT achieved the highest performance in collecting Anopheline mosquitoes at 1.54 times compared to OHLC, but there was no significant difference between the two traps. The results suggested HDNT could be a possible alternative trap to OHLC in this area. Although HDT was less efficient at attracting Anopheline mosquitoes, it was highly efficient at trapping culicine mosquitoes.

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BACKGROUND: Surveillance of outdoor host-seeking malaria vectors is crucial to monitor changes in vector biting behaviour and evaluate the impact of vector control interventions. Human landing catch (HLC) has been considered the most reliable and gold standard surveillance method to estimate human-biting rates. However, it is labour-intensive, and its use is facing an increasing ethical concern due to potential risk of exposure to infectious mosquito bites. Thus, alternative methods are required. This study was conducted to evaluate the performance of human-odour-baited CDC light trap (HBLT) and human-baited double net trap (HDNT) for outdoor host-seeking malaria vector surveillance in Kenya and Ethiopia. METHODS: The sampling efficiency of HBLT and HDNT was compared with CDC light trap and HLC using Latin Square Design in Ahero and Iguhu sites, western Kenya and Bulbul site, southwestern Ethiopia between November 2015 and December 2018. The differences in Anopheles mosquito density among the trapping methods were compared using generalized linear model. RESULTS: Overall, 16,963 female Anopheles mosquitoes comprising Anopheles gambiae sensu lato (s.l.), Anopheles funestus s.l., Anopheles pharoensis, Anopheles coustani and Anopheles squamosus were collected. PCR results (n = 552) showed that Anopheles arabiensis was the only member of An. gambiae s.l. in Ahero and Bulbul, while 15.7% An. arabiensis and 84.3% An. gambiae sensu stricto (s.s.) constituted An. gambiae s.l. in Iguhu. In Ahero, HBLT captured 2.23 times as many An. arabiensis and 2.11 times as many An. funestus as CDC light trap. In the same site, HDNT yielded 3.43 times more An. arabiensis and 3.24 times more An. funestus than HBLT. In Iguhu, the density of Anopheles mosquitoes did not vary between the traps (p > 0.05). In Bulbul, HBLT caught 2.19 times as many An. arabiensis as CDC light trap, while HDNT caught 6.53 times as many An. arabiensis as CDC light trap. The mean density of An. arabiensis did not vary between HDNT and HLC (p = 0.098), whereas the HLC yielded significantly higher density of An. arabiensis compared to HBLT and CDC light trap. There was a significant density-independent positive correlation between HDNT and HLC (r = 0.69). CONCLUSION: This study revealed that both HBLT and HDNT caught higher density of malaria vectors than conventional CDC light trap. Moreover, HDNT yielded a similar vector density as HLC, suggesting that it could be an alternative tool to HLC for outdoor host-seeking malaria vector surveillance.

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Objective: Monitoring the density of Aedes(Ae.) albopictus was very important in evaluating the efficiency of vector management, especially when Aedes-borne diseases break, like Dengue fever, Chikungunya fever and Zika. Human landing catch (HLC) is regarded as the “gold standard” for Aedes monitoring, but it is unsafe and unethical since it potentially expose field professionals to a series of pathogens. In this study, we compared HLC with human-baited double net (HDN) and BG trap for field Aedes albopictus monitoring.The study aims to find an effective and safe alternative method to HLC in monitoring Ae. albopictus, especially in emergency monitoring. Methods: Latin square design was used, and three sites in Hangzhou city, Zhejiang province, China, were chosen to conduct outdoor HLC, HDN and BG trap catches in June. The tests were performed at three periods: a morning period (8:30-10:00), an afternoon period (15:00-16:30), and an evening period (16:30-18:00). Then a table with 81 elements was made to compare the efficiency of these three methods. Results: A total of 80, 138 and 78 adult Ae. albopitus was captured by HDN, BG trap and HLC, respectively. Among these three catches, BG trap showed the best efficacy in captured Ae. albopitus adults. The mosquitoes caught by HLC and BG trap were nearly the same at all three time series, but the density of mosquitoes caught by HDN at 16:30-18:00 was 2 times the density at 8:30-10:00 (4.44 vs 2.22 per hour). In this study, significant positive correlation between HLC and BG trap of Aedes albopitus female density was found (r=0.921, P<0.001). However, no statistical significant correlation between HLC and HDN, BG trap and HDN of Ae. albopitus female density was found (r=-0.46, P=0.820; r=0.019, P=0.923, respectively). Besides, the human-bait attraction bias of HLC catches might be more apparent than BG trap and HDN catches. Conclusions: According to our study, with high efficiency, less human-bait attraction bias, and significantly positive correlation with HLC in catching Ae. albopitus females, BG trap could be a sensitive and safer alternative to HLC for outdoor Ae. albopitus monitoring. It also showed strong potential in emergency monitoring when Aedesborne diseases break.

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BACKGROUND: Human landing catch (HLC) is the most efficient method for Aedes monitoring, but it is not ethical due to its high risk of human exposure to pathogens. We designed trials to assess the performance of an alternative human-baited double net trap (HDN) for field Aedes albopictus monitoring compared with the standard HLC. METHODS: Outdoor HDN and HLC catches were conducted simultaneously at 15 field sites on two sunny days in mid-July and August. The tests were performed 3 h apart: an early morning period (7:30-8:30 h), a pre-sunset period (16:30-17:30 h) and a post-sunset period (18:30-19:30 h). A total of 90 comparisons were made between the two methods. Field comparisons were designed to minimize half-hour bias and human-bait attraction bias. RESULTS: Two mosquito species were collected by HDN and HLC, with the predominated species being Ae. albopictus (HDN: n = 1325, 97.35% of total; HLC: n = 531, 92.51% of total). A small proportion were adults of the Culex pipiens complex (HDN: n = 36, 2.65% of total; HLC: n = 43, 7.49% of total). Although the mean Ae. albopictus catch per hour of HLC was significantly higher than HDN (14.72 vs 5.90 per h, t(178) = 3.151, P = 0.003), there were significant positive spatial and temporal correlations between HLC and HDN for Ae. albopictus sampling among different sites and hours (r(90) = 0.785, P < 0.001; r(90) = 0.785, P < 0.001). Both methods proved that Ae. albopictus was most active during the hours before sunset and least active after sunset. No significant variation was observed in Ae. albopictus catch size of HDN between groups of more attractive and less attractive humans (3.38 vs 2.51 per 30 min, t(88) = 1.283, P = 0.201). CONCLUSIONS: With moderate sampling efficiency, significantly positive spatial correlation with HLC, and less human-bait attraction bias, HDN appears to be a safer alternative to HLC for Ae. albopictus monitoring in Shanghai. With mosquito activity peaking in the pre-sunset hours, Ae. albopictus catches of HDN should be performed in the hours before dark. The trap design could be improved to make it more portable and easier for field operation.

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