Context
A total of 160 biological records (3,806 specimens) of the immature stage (pupae) of Ae. aegypti were collected from dwellings in the municipalities of Patía (El Bordo), Miranda, and Piamonte, within the department of Cauca, in the southwest of Colombia. These municipalities are part of an ongoing research project titled “Spatial stratification of dengue based on the identification of risk factors: a pilot trial in the department of Cauca” headed by the Entomology Group of the National Institute of Health, the Secretary of Health of Cauca, and the University of Applied and Environmental Sciences (UDCA). Among other objectives, this project seeks to evaluate the robustness of the link between entomological variables, which explains the spatial pattern observed in the distribution of dengue fever.
The data were collected between 2021 and 2022 by a multidisciplinary team of environmental health technicians, geographic and environmental engineers, and professionals with extensive experience in medical entomology. In this dataset, we distinguish three sampling periods for each municipality. For Patía: March and October 2021, and March and April 2022; for Miranda: April and November 2021, and May 2022; and for Piamonte, July 2021, and February and July 2022. A fourth sampling period was performed in August and October 2022 in the municipalities of Patía and Miranda, respectively, to increase the sample size to carry out the serotyping of the specimens.
The immature stages (pupae) were collected from the inspection of containers smaller or larger than 20 l, including tanks, drums, and tires, among others, from inside the houses of three municipalities. The municipalities were selected as study areas based on their endemic-epidemic behaviours for DENV transmission, as they are characterized by focal endemics, heterogeneous transmission scenarios, and temporal and cyclical patterns of at-risk populations.
The resulting pupae dataset is in Darwin Core file format, with 73 terms available. We included all mandatory fields, which were submitted to the Integrated Publishing Toolkit (IPT) for review by SiB-Colombia. Metadata fields are also available from the IPT website
[15]. A total of 3,480 adult individuals of the family Culicidae are included in this dataset. Of these, about 69% of the specimens were previously reported in 2021
[16], while 1,078 are the new records collected in 2022.
These biological registers are fundamental for the scientific community as they provide the geographical coordinates and entomological indices necessary for the public health surveillance performed by health entities. In particular, these measures are essential for preventing and controlling the etiological agent from houses and neighbourhoods with high infestation rates.
Methods
Sampling
The specimens of the immature stages of the
Ae. aegypti pupae belonged to dwellings located in the municipalities of Patía (El Bordo), Miranda, and Piamonte, within the department of Cauca, Colombia (Figure
1). These municipalities were selected because they were considered endemic-epidemic with a high dengue transmission risk after conducting a spatiotemporal analysis
[16]. The sample size was delimited spatial scale of blocks by Kernel density analysis, georeferencing the dengue cases reported from 2015 to 2019 in the urban areas of each municipality. Additionally, the sample size was calculated from the estimated prevalence of dengue (10.5%) in the municipality
[17] with a confidence level of 99% calculated by the Epi Info™ software, using the estimated population size and the clusters obtained in the Kernel analysis.
Figure 1.
In total, 1,919 dwellings were visited in 26 neighbourhoods during March, April, July, and October 2021, and February, March, May, July, August, and October 2022. In the municipality of Patía, 11 neighbourhoods were visited (n = 580 households), in Miranda 12 neighbourhoods (n = 854 households), and in Piamonte four neighbourhoods (n = 485 households).
Species collection
A survey of the dwellings was carried out during the day between 8:00 a.m. and 5:00 p.m. Then, the parameters stipulated in the guide Management for the entomological surveillance and control of dengue transmission were followed
[7, 10]. Artificial water containers found in the households were selected. All breeding sites were inspected regardless of their size, i.e., containers smaller than 20 l, such as bottles, vases, cans, tires, and small plastic containers. The pupae were collected with a Pasteur pipette and then counted. For containers larger than 20 l, the number of pupae collected with a sweep net was counted, and the volume of the tanks for water storage (TWS) and the existing water level were evaluated to calculate the calibration factor
[7] and obtain the estimated number of pupae or the pupal productivity.
Entomological inspections for adult mosquitoes were conducted during specific months in 2021 (February, March, April, July, October, and November) and 2022 (February, March, May, and July). These inspections were performed between 8:00 a.m. and 5:00 p.m., averaging 10 min per house. In each dwelling, a search for adult mosquitoes was conducted in the living room, dining room, bathrooms, kitchens, laundry yard, and other areas; the mosquitoes were captured using a Prokopack aspirator. Using these procedures, during the examination, special attention was directed toward exploring shaded areas and locations near water containers.
Species classification and spatial characterization
After the collection of the immature stages (pupae) and adults, the species were identified and taxonomically classified by entomological experts supported by the taxonomic keys developed by Forattini
[19] (1995) and Harrison
et al. [20] (2016) to differentiate them from the immature stages and adults belonging to other species. Continuing with the field protocol, 3,806 pupae of
Ae. aegypti were identified, of which 395 were preserved in 0.2 ml vials with RNAlater
© for subsequent processing with molecular biology techniques at the Entomology group and the Genomics of Emerging Microorganisms group of the National Institute of Health (Bogotá, Colombia)
[21].
The entomological information collected was recorded using the ArcGIS
® Survey 123 application
[22], which provided the geographic location of each specimen collected. A code was associated to each vial with the socio-demographic information of the survey. The total number of pupae recorded in each survey was used to determine the entomological indices of pupal productivity, female productivity, pupal index per person, Breteau’s pupal index
[7, 10], and
Aedes sp. pupae sex ratio F:M (Table
1).
Table 1
Indicators for
Ae. aegypti entomological surveillance
[7, 9, 10].
Index | Calculation | Interpretation |
---|
Pupal productivity | (Number of pupae in the container type * calibration factor) | Calculate the estimated number of pupae per container. For deposits smaller than 20 l, only the number of pupae is counted. For deposits larger than 20 l, multiply the number of pupae by calibration factor (c.f.) provided by water level. Water levels: <1/3 c.f. not applicable; 1/3 c.f.: 2.6; 2/3 c.f.: 3.0; 3/3 c.f.: 3.5. |
Female pupae productivity | (Number of pupae assuming a 1:1 sex ratio at emergence) | Estimate the number of emerging adult mosquito females produced per container. |
Pupae-per-person index | (Pupal productivity/total population of the screened houses) | Generate an estimate of the number of pupae per person in the screened household. |
Breteau Index | (Number of containers with any pupae *100/Number of screened houses) | Defined as total number of positive containers per 100 households inspected. Determined by a ratio of positive containers to screened households. |
The entomological information, together with the geographical block information of the municipalities, was used to perform scatterplot analyses (
R2, slope
b,
p-value), as well as scatterplot matrices to evaluate the relationships between entomological variables: number of adult
Ae. aegypti mosquitoes
[18], total number of pupae, pupal productivity, female productivity, and number of pupae per person vs. the frequency of tanks for water storage, miscellaneous containers smaller than 20 l, and drums.
A global bivariate Moran Index analysis (
p ≤ 0.05) was performed to detect the distribution of variables related to spatial clustering. The Moran Index ranges from −1 to 1, where −1 indicates dispersed clustering patterns, 0 indicates randomness, and 1 suggests perfect association. Next, a Local Moran Index analysis distributed the significant (
p = 0.05) clusters of dwelling blocks into four types of local spatial association. (I) high(
x)-high(
y) indicates areas with high values of the variable (
x) surrounded by values above the mean of the variable under analysis (
y); (II) low(
x)-high(
y) indicates areas with low values of the variable (
x) surrounded by neighbouring areas with values above the mean of the variable (
y); (III) low(
x)-low(
y) indicates areas with low values of the variable (
x) surrounded by areas with values below the mean of the variable (
y); and (IV) high(
x)-low(
y) indicates areas with high values of the variable (
x) surrounded by areas below the mean of the variable (
y)
[13].
The above analyses were performed for two sampling periods in each municipality. For the municipality of Patía (El Bordo), samples were collected in March and October 2021, for Miranda samples were collected in April and November 2021, and for Piamonte samples were collected in July 2021 and February 2022, since the rainfall pattern was seasonal between these months. Finally, the analyses were performed using the GeoDa v1.20 program
[23] and the maps were visualized using the ArcGIS
® 10.8 software (RRID:
SCR_011081).
Data validation and quality control
A total of 3,480 adult specimens were identified across 1,200 households, comprising 1,459 females and 2,021 males. In 2021, 2,402 records were documented, while 1,078 new records were added in 2022. In terms of municipal distribution, Miranda reported 500 individuals (14.36%), Patía 1,305 (37.5%), and Piamonte had the highest count with 1,675 (48.13%) adult individuals. Notably, 71 individuals were found within a Patía household, and an additional 125 individuals were identified within a different household in Piamonte.
Moreover, a total of 3,806 immature specimens (pupae) of
Ae. aegypti were identified, distributed among 160 records (positive dwellings out of the total inspected). For the municipality of Patía (El Bordo), 1,493 individuals were found in 67 positive dwellings, for Miranda 1,173 individuals were in 58 dwellings, and for Piamonte 1,140 individuals were found in 35 dwellings. The neighbourhoods with the highest number of specimens were Villa Los Prados (
n = 519) and La Paz (
n = 359) in Piamonte, followed by the San Antonio neighbourhood (
n = 391) in Miranda, and the Libertador (
n = 441) and Olaya Herrera (
n = 438) neighbourhoods in Patía. It should be noted that 70 of the inspected dwellings were found with more than 15 pupae inside the house. The largest number of detected specimens belonged to a house in the municipality of Piamonte, with 280 pupae (Table
2).
Table 2
Descriptive entomological measures by sampling locality. The total of positive screened houses for each mosquito species is shown as a total and as a percentage for each municipality
[24, 25].
Entomological measure | Municipality | Total |
---|
| Patía | Miranda | Piamonte | |
---|
Number of houses screened | 580 | 854 | 485 | 1919 |
Number of habitants in screened houses | 2098 | 3735 | 1880 | 7713 |
# of positive houses with Aedes sp. pupae (%) | 67 (11.55%) | 58 (6.79%) | 35 (7.22%) | 121 |
Number of containers screened | 1142 | 1067 | 984 | 3193 |
# of positive containers with Aedes sp. Pupae (%) | 50 (4.38%) | 43 (4.03%) | 36 (3.66%) | 129 |
Total #of Aedes sp. pupae | 425 | 530 | 389 | 1344 |
Aedes sp. pupae productivity | 1493 | 1173 | 1140 | 3806 |
Aedes sp. pupae sex ratio F:M [21, 22] | 1:1 | 1:1 | 1:1 | 1:1 |
Number of pupae per person | 0.71 | 0.31 | 0.61 | 1.63 |
Breteau index | 8.62 | 5.04 | 7.42 | 21.08 |
For the wet season of the sampling, our spatial regression analysis found a positive correlation for the municipalities. Specifically, the determination coefficient between the captures of pupae and adults was higher than 50% in the municipalities of Patía (R = 0.7292; R2 = 0.53) and Miranda (R = 0.7486; R2 = 0.56) and lower in Piamonte (R = 0.4252; R2 = 0.18), highlighting the relevance of the adult index for entomological surveillance. In addition, a spatial autocorrelation was observed between the presence of pupa-positive houses and a higher density of adults in neighbouring blocks.
For the Patía municipality, the variable productivity of female pupae explained the number of adult mosquitoes with a model adjustment of 53.2% in the period of higher rainfall and with an adjustment of 8.4% in the period of lower rainfall, presenting in both cases positive autocorrelation between the variables (Table
3). This allowed us to locate the clusters in which pupal productivity generated a high mosquito density at the block level (Figure
2).
Table 3
Results of the regression analysis and the bivariate spatial autocorrelation for entomological variables of Ae. aegypti in Patía, Miranda, and Piamonte, according to the seasonality of sampling.
Municipality | Seasonality | Variables (X, Y) | Parameters | Moran I (MI) |
---|
| | | R2 | Slope b | p value | |
---|
Patía (El Bordo) | Wet season higher precipitation March 2021 | % TWS - PPPPupal productivity ♀ - PPP% TWS - No. adult mosquitoes% TWS - Pupal productivity ♀Pupal productivity ♀ - No. adult mosquitoes | 0.2320.3270.1260.3740.532 | 0.0820.3130.0530.1910.530 | 0.000*0.000*0.006*0.000*0.000* | 0.264
0.325
0.132
0.109
0.108 |
| Wet season lower precipitation October 2021 | % TWS - PPPPupal productivity ♀ - PPP% Flower vases - PPP% Flower vases - Pupal productivity ♀Pupal productivity ♀ - No. adult mosquitoes | 0.5600.6800.2620.1500.084 | 0.1060.2620.5870.7010.145 | 0.000*0.000*0.000*0.004*0.035* | −0.048 0.034
0.033
0.115
0.196 |
Miranda | Wet season lower precipitation April 2021 | Pupal productivity ♀ - No. adult mosquitoes% TWS - No.adult mosquitoesPupal productivity- No. adult mosquitoes (♀) | 0.560.1160.437 | 0.1140.070.028 | 0.000*0.001*0.000* | 0.086
0.051
0.043 |
| Wet season higher precipitation November 2021 | Pupal productivity ♀ - No. adult mosquitoes% TWS- number of adult mosquitoesPupal productivity - No. adult mosquitoes (♀) | 0.0430.0000.045 | 0.366-0.0030.145 | 0.0640.9650.058* | −0.035 −0.029 −0.047 |
Piamonte | Wet season higher precipitation July 2021 | Pupal productivity ♀ - No. of adult mosquitoes% miscellaneous containers < 20L - PPP% drums-Pupal productivity ♀ | 0.1810.0010.054 | 0.037-0.0631.026 | 0.004*0.8090.123 | 0.058
0.054
0.043 |
| Dry season lower precipitation February 2022 | Pupal productivity ♀ - No. adult mosquitoes% miscellaneous containers 20L - PPP% drums-Pupal productivity ♀% buckets-Pupal productivity ♀ | 0.1970.0060.1070.377 | 0.0850.0040.2471.357 | 0.005*0.6430.042*0.000* | 0.044
0.124
0.112
−0.026 |
Figure 2.
Bivariate local Moran index for the variables pupal productivity (x) and number of adult mosquitoes (y) in the municipalities of Patía, Miranda, and Piamonte (2021–2022).
Variables such as the frequency of positive vases when rainfall reached only 1 mm (October 2021) explained the female pupal productivity by only 15%. However, in the period of higher precipitation (211 mm, March 2021), the tank container explained 37% of the female pupal productivity and, subsequently, the density of adult mosquitoes. This comparison is interesting, considering that the climate of the Patía municipality is bimodal, with peaks in April and November
[26]. Our local analysis (LISA) observed heterogeneous high-high and low-low spatial clusterings for each season, mainly in the Olaya Herrera neighborhood (March and October 2021).
The model for the municipality of Miranda showed an
R2 model fit of 56% and a positive spatial autocorrelation in the season of lower rainfall, although with a high percentage of relative humidity, among the variables of female pupal productivity, explaining the number of adult mosquitoes. Positive autocorrelation was also found for the variables frequency-of-positive-low-TWS and pupae-productivity. However, for the period of higher precipitation and lower relative humidity, a negative spatial autocorrelation was found for the variables evaluated, i.e., with clustering patterns close to randomness (Table
3).
For Piamonte, during the wet season, the female-pupal-productivity variable explained the model fit (R2) by 18%, with a positive bivariate spatial autocorrelation (Moran Index (MI) = 0.058). Miscellaneous containers smaller than 20 l, drums, and TWS presented non-significant positive autocorrelation of entomological indicators and number of adults. This latter finding is in contrast with the correlation between the percentage of positive buckets and pupae productivity (R2 = 37.7%) in the dry season of sampling.
These findings suggest that for the species
Ae. aegypti, pupal productivity generates high densities of adults in neighbouring houses, allowing us to identify with the local indicator of spatial association (LISA) the blocks of neighbourhoods where this trend occurs, evidencing seasonal behaviour. While the spatial correlation linked the capture of pupae and adults in the same geographical space, the bivariate autocorrelation (MI) related these same variables, without necessarily coinciding in the same dwelling. Likewise, between municipalities, a greater positive spatial autocorrelation between pupae and adults was observed in Patía, especially when precipitation decreased before the onset of the rainy season. Our results are similar to other spatiotemporal studies of mosquito density
[13, 27], showing heterogeneous patterns of occurrence for each territory, with seasonal behaviours registering higher infestation rates in seasons of higher rainfall.
Re-use potential
Our database and vector distribution map provide important resources for understanding the spatial patterns of the vector and its relationship with entomological indicators and breeding sites, which could increase dengue virus transmission in the municipalities.
To improve the accessibility and usability of these data, they have been included in the GBIF. These data will be useful for making representative approximations of mosquito densities, mapping areas with high increases in pupal productivity, and linking other environmental, entomological, or socio-demographic determinants, providing essential information to generate innovative strategies for prevention, vector control, and management of dengue. We suggest others make their data available as well.