An improved ovitrap-based surveillance framework: facilitating cost-efficient monitoring and efficacy assessment of integrated vector management strategies for dengue outbreak control | Parasites & Vectors

IMT design specifications

The IMT design is fundamentally grounded in the oviposition behavior of Ae. albopictus and its adaptability to varying weather conditions and the subsequent management of collected eggs. Compared with conventional ovitrap models, this IMT design is characterized by a larger container volume (5 L; upper diameter: 215 mm, lower diameter: 165 mm, height: 245 mm; Fig. S1). This large volume of container was specifically made in black to create a more alluring breeding environment for Ae. albopictus [25] because of the preference of this species for dark-colored oviposition sites [26].

The oviposition carrier was deliberately designed to account for the oviposition behavior of Ae. albopictus, because these mosquitoes lay eggs on the container edge rather than directly in water, unlike Ae. aegypti [27]. To address the limitations of disposable filter papers in MOTs (e.g., powdery residue, cumbersome egg collection), the IMT incorporates a reusable, deep blue thermoplastic elastomer (TPE) oviposition strip (550 mm × 40 mm × 10 mm; Fig. S1). This oviposition strip features distinct surface characteristics: a smooth outer face for optimal bucket adhesion and an inner face with transverse stripes spaced 6.5 mm apart. When deployed, the strip forms a circular configuration with (1) the smooth exterior pressed against the container wall and (2) the textured interior floating at the water interface. This design provides an inclined oviposition surface that significantly reduces egg displacement into the water column.

The oviposition band/strip maintains optimal positioning relative to water level fluctuations in tropical/subtropical habitats across variable weather conditions. For deployment, (1) the container was filled with clean water to 40–50% capacity, and (2) the substrate was secured vertically along the inner wall to ensure continuous flotation on the water surface.

Field study to evaluate the effectiveness of the IMT

Investigation areas

Two field investigations focusing on Ae. albopictus were conducted in Guangzhou, Guangdong Province, China (Fig. 1a). This city features a subtropical monsoon climate typically with four distinct seasons. Summers are characterized by high temperatures and heavy rainfall, whereas winters are mild and humid. With an annual mean temperature of 21.6 °C and an average annual rainfall of approximately 1980 mm, these conditions provide an ideal environment for the breeding and growth of Ae. albopictus mosquitoes.

Investigation sites and the environments for evaluating the effectiveness of IMT in Guangzhou. a Two field investigations encompassing seven sites involving Ae. albopictus were conducted in Guangzhou. b Five sites and surrounding environments of field investigation 1. c Two sites and surrounding environments of field investigation 2

For field investigation 1, we selected five sites, including Tonghe (TOH; 23.185734N, 113.334702E), Huanghuagang (HHG; 23.141904N, 113.298651E), Hepingxincun (HPX; 23.138515N, 113.237929E), Tangjing (TAJ; 23.167231N, 113.255696E), and Xiangjinghuayuan (XJH; 23.203722N, 113.267219E), were selected for field investigation 1 (Fig. 1a, b). HHG, HPX, TAJ, and XJH were residential areas, whereas TOH was a school area (Fig. 1b). For field investigation 2, two sites, Nanyidagongyu (NYD; 23.190295N, 113.335764E) and Yunjinghuayuan (YJH; 23.184511N, 113.329757E), were selected (Fig. 1a, c). Both NYD and YJH were residential areas (Fig. 1c).

Field investigation 1: continuous field mosquito surveillance to assess the effectiveness of IMT

A network of 71 IMTs was established across five investigation sites from July 2020 to October 2020 (Fig. 1b). The traps were placed in the mixed locations weekly. After 7 days, the samples were sent to our laboratory for assessment of the presence of mosquito eggs, larvae, and adults. To observe the distribution of mosquito eggs on the strip, manual counting was conducted using counters. A Pasteur pipette was used to rinse the eggs off the strip with clean water onto filter paper. Once the water had completely drained, the eggs were collected and stored at −20 °C for more than 24 h to ensure complete inactivation.

Field investigation 2: comparative monitoring effectiveness of IMT versus MOT for Ae. albopictus

We employed a spatially interspersed deployment strategy for the IMT and MOT traps within their natural habitats (Fig. 1c). Eggs were collected from September 2024 to December 2024 and subsequently transported to the laboratory for counting (Fig. 1c). The IMT and MOT traps were consistently placed in fixed locations each time. After 4 days of deployment, the traps were retrieved and sent to the laboratory for assessment of mosquito developmental stages.

Distance incremental spatial autocorrelation analysis

Moran’s index (Moran’s I) quantifies the spatial similarity between neighboring units in space by assessing the correlation between their spatial locations and sample values. Specifically, it is computed as the product of the difference between each unit’s value and that of its adjacent units. As Moran’s I approaches the boundary value of its range, it signifies a stronger aggregation effect for the variable. Conversely, when Moran’s I deviates from this boundary value, it indicates a weaker aggregation effect.

To assess the presence of spatial autocorrelation (SA) in the IMT, we computed Moran’s I [28]. Moran’s I is a correlation coefficient that characterizes whether attribute values exhibit significant dispersion, randomness, or clustering in space [29]. The range of Moran’s I varies from −1 to 1, where negative values indicate a dispersed spatial pattern, 0 signifies a random pattern, and positive values denote a clustered pattern. The magnitude of Moran’s I reflects the strength of the spatial pattern, with larger positive values (closer to 1) suggesting more pronounced clustering of similar attribute values [29]. The Moran’s I value of 0.2 is a threshold for determining whether there is a correlation [29]. The formula for calculating Moran’s I is as follows:

, where n is the number of features, S₀ is the sum of all spatial weights, i and j denote two features, w_i,j is the spatial weight between those features, and z is the deviation of the attribute at that feature from the mean.

We performed incremental spatial autocorrelation analysis by calculating Moran’s I for IMTs across successive distance thresholds, beginning with 50-m intervals and systematically expanding the range by 10-m increments (50 m, 60 m, 70 m, etc.) until maximum sampling distance was covered.

The statistical significance of Moran’s I was determined by P-values or z-scores. By considering the number of pairwise IMTs within each bin and the variance between the expected and observed Moran’s I values, this tool calculates a P-value to determine if there is a statistically significant difference. The resulting Moran’s I and P-values at each incrementally larger distance bin enable us to identify the scale at which spatial autocorrelation occurs. The Moran’s z-score was calculated as the standardized value of the local Moran’s I index, which is used to assess whether the observed spatial pattern exhibits clustering, dispersion, or randomness.

Estimation of the suitable sampling fractions

Although advanced point-selection algorithms exist (e.g., sequential selection, simulated annealing, and generalized random tessellation stratification), their complexity often limits their practical implementation. We therefore adopted a simplified sampling strategy, with layout optimization guided by relative error (RE) minimization in population extrapolation.

IMT-based surveillance strategy for case-area targeted interventions (CATIs)

In resource-limited settings, the implementation of CATIs offers a strategic approach to outbreak control by concentrating efforts on areas with recent disease cases [30]. Technical guidance documents such as the “Technical Guidelines for Dengue Fever Prevention and Control” released by the Chinese Center for Disease Control and Prevention [31], and the “Professional Technical Guidelines for Dengue Fever Prevention and Control in Guangdong Province” issued by the Guangdong Provincial Health Commission [32], organize interventions across three concentric zones: core, alert, and surveillance. The core zone encompasses a 200-m radius around infected individuals’ residences or workplaces, corresponding to the typical flight range of Aedes mosquitoes. This central area is surrounded by an alert zone extending an additional 200 m outwards, with rural implementations covering natural villages progressing to administrative units as needed, whereas urban deployments typically include adjacent streets and neighborhoods. Beyond these areas, a surveillance zone is established with monitoring intensity adjusted according to seasonal transmission risks.

During CATI execution, broad investigations are conducted using a standardized questionnaire to document patient activities and mosquito-bite history. Research results are complemented by laboratory tests of patient serum and captured mosquitoes. Active case detection involves systematic searches with a 200-m core radius, including checks at local healthcare facilities. When warranted, serological surveys are performed to assess transmission dynamics, with preliminary epidemiological reports required within 24 h of case identification and follow-up updates as the investigation progresses. Intervention effectiveness is monitored using key indicators, including case incidence and mosquito density metrics, with outbreak resolution declared only after 21 consecutive days without new cases and confirmation of a Breteau index (BI) below 5.

In our study, we collaborated with the Shenzhen Luohu CDC to integrate IMTs into the CATI framework across the core and alert zones of two active transmission areas in Shenzhen, China. We collected mosquito eggs on a daily basis and identified their species, with continuous monitoring maintained until local health authorities officially concluded the intervention period.