Entomological Assessment of the Risk of Dengue Epidemic in the Lawspet Constituency,Puducherry

Introduction

Vector-borne diseases (VBDs) make up 17% of the global burden of all infectious diseases. Every year, about 7,00,000 deaths are happening due to these VBDs such as dengue, malaria, schistosomiasis, Japanese encephalitis, leishmaniasis, etc. (ScienceDirect Topics, 2026). Dengue remains as a significant public health problem in India, fluctuating over the years with 32,091 cases and 32 deaths reported until June 2024 (National Centre for Vector Borne Diseases Control, 2024). VBDs especially mosquito-borne diseases (MBDs), are commonly found in tropical and subtropical regions due to the favorable conditions for vector proliferation and survival (Chua et al., 2023). Dengue virus (DENV) belongs to the family Flaviviridae and is a single-stranded RNA virus with four serotypes (Murugesan and Manoharan, 2020). The mosquito species responsible for the transmission of DENV are Aedes aegypti and secondarily, through the Asian tiger mosquito Aedes albopictus (World Health Organization, 2024a). These mosquito species breeds in small containers collected with rain water or in man made containers with water kept open (Sinha et al., 2024).

Puducherry reported its first dengue outbreak in 2003 and since then regular outbreaks have been reported with major outbreaks in 2011 (463 cases) and in 2012 (3506 cases) (National Centre for Vector Borne Diseases Control, 2024). A study by Indian Council of Medical Research-Vector Control Research Center showed that there is a lack of in-depth knowledge on dengue in the community (Jeelani et al., 2015). Further larval indices have been found to vary throughout the year and the highest indices were found out in the month of October (House index [HI]-35.6, Container index [CI]-17.9, and Breteau index [BI]-49.8) and November (HI-35.7, CI-20. 2, and BI-52.3), which indicated a high risk of dengue fever during this period (Jeelani and Sabesan, 2016).

The incidence of dengue is not solely dependent on Aedes spp. abundance and the frequency of contact between vectors and susceptible human hosts, and is also influenced by the vectorial capacity of the mosquito population, which is defined by vector density, human biting rate, adult mosquito survival, vector competence for DENV transmission, and the extrinsic incubation period of the virus within the mosquito, and is reflected by the positive correlation between Aedes spp. abundance and dengue prevalence (World Health Organization., 2024), therefore, the ideal way to prevent the transmission of DENV is to combat Aedes mosquitoes (Ghosh et al., 2019). Hence, these necessitates the entomological surveillance to assess and predict the abundance of vectors and the future occurrence of dengue. Hence, a study was aimed to determine the larval indices of immatures of Aedes spp. from the hotspot area of Lawspet constituency, Puducherry.

Materials and Methods

Study area

Puducherry, a small coastal town in Southern India, has a predominantly hot and humid climate throughout the year, with average temperatures ranging from 26°C to 38°C (Ali et al., 2022). Lawspet constituency has been recognized as a dengue hotspot in Puducherry, highlighting a significant public health issue in the area. Hence, the study area was selected in Pedhuchettipett one of the four wards of Lawspet constituency, which lies between 11.956956° North and 79.820572° East to conduct the Aedes immatures survey. Pedhuchettipet ward (Fig. 1) is comprised of a total of 960 households and has a population of about 4500 residents.

OPEN IN VIEWER

FIG. 1.

Pedhuchettipet ward of Lawspet Constituency (Study area is given in the red).

Sample collection

A door-to-door Aedes immature survey was undertaken following the standard operating protocols established by the World Health Organization (WHO) (Jeyapal et al., 2022) for entomological surveys in 464 houses of the ward. The survey was conducted during the months of April to May 2024, which correspond to the summer season in Puducherry.

Survey was carried out in 464 houses in total of 19 streets namely Akbar street (n = 21), Bharathi street (n = 21), Chozhan street (n = 24), Gandhi street (n = 22), Ilango Adigal street (n = 26), Kattabomman street (n = 49), Kavimani desiga vinayagam pillai street (n = 26), Maraimalai Adigal street (n = 19), Mugambai kovil street (n = 3), Outhukathu mariamman kovil street (n = 35), Pandian street (n = 10), Parivallal street (n = 39), Sivaji street (n = 3), Sri krishna street (n = 22), Thiru vi ka street (n = 30), VOC street (n = 9), Venkateshwara street (n = 16), Vinayagar kovil street (n = 58), Viyasar street (n = 31).

In Pedhuchettipet ward, a street-based systematic contiguous sampling approach was used to cover approximately half of the streets in the ward (Table 1) during the summer months of April and May, and along these streets, all accessible households were visited in a consecutive sequence.

OPEN IN VIEWER

Table 1.

House Index and Breteau Index Based on Streetwise Data

Street name	Number of houses examined	No. of positive houses	No. of positive container	No. of pupal positive container	House index (%)	Breteau index (%)
Akbar street	21	0	0	0	0.0	0.0
Bharathi street	21	1	1	0	4.8	4.8
Chozhan street	24	1	1	0	4.2	4.2
Gandhi street	22	1	1	0	4.5	4.5
Ilango Adigal street	26	0	0	0	0.0	0.0
Kattabomman street	49	2	3	1	4.1	6.1
Kavimani desiga vinayagam pillai street	26	1	2	1	3.8	7.7
Maraimalai Adigal street	19	0	0	0	0.0	0.0
Mugambai Kovil street	3	0	0	0	0.0	0.0
Outhukathu mariamman Kovil street	35	2	2	1	5.7	5.7
Pandian street	10	1	1	1	10.0	10.0
Parivallal street	39	2	3	0	5.1	7.7
Sivaji street	3	0	0	0	0.0	0.0
Sri krishna street	22	0	0	0	0.0	0.0
Thiru vi ka street	30	2	2	2	6.7	6.7
VOC street	9	1	1	0	11.1	11.1
Venkateshwara street	16	0	0	0	0.0	0.0
Vinayagar Kovil street	58	1	1	0	1.7	1.7
Viyasar Street	31	2	6	1	6.5	19.4
Total	464	17	24	7	—	—

Within each selected street, neighboring houses were examined one after another until the intended coverage for that street was reached, resulting in a total of 464 surveyed households, representing 48.3% of all households in the ward. This systematic, street-based contiguous sampling strategy was chosen to achieve broad spatial coverage and operational feasibility, while providing an adequate sample size for calculating the HI, CI, and BI to assess the risk of dengue transmission in the area.

The immature survey was carried out in the house premises (Fig. 2), terrace, balcony, in the construction sites as Aedes immatures are container breeders, all the containers such as flower pot (FP), discarded plastic containers (DPC), discarded utensil (DU), discarded drum (DDR), discarded bottles (DB), discarded tire (DT), grinding stone (GS), cement tank (CT), and overhead syntex tank (OHTS), etc. Containers that contained eggs, larvae or pupae were classified as positive containers, while those without eggs, larvae, or pupae were classified as negative containers. Containers found with water were labeled as wet containers, and those without water were referred to as dry containers. All data were accurately entered into the Aedes immature survey format within the designated timeframe and subsequently entered into Microsoft Excel program.

OPEN IN VIEWER

FIG. 2.

Various breeding sites of Aedes immatures.

Results

This study was conducted in one of the four wards of the larger study site in the Lawspet constituency. From a total of 464 houses inspected in the study area, 17 houses were found to be positive for larvae/pupae in 24 containers. A total of 200 immatures emerged, and all were identified as Ae. aegypti, indicating that only Ae. aegypti species were present in this study site. The emergence rate was 60% of the immatures, indicating suitable laboratory conditions were provided as that of the field for the emergence of Ae. aegypti.

From the entomological indices calculated, the overall HI and BI were 3.6% and 5.17%, respectively, and the CI was 4.36%. The HI value was below the threshold of 4%, indicating a low risk of epidemic transmission, whereas the BI and CI values fell within their respective moderate-risk ranges, suggesting a moderate risk of an epidemic. Furthermore the results of street-wise data on HI and BI (Table 1) showed that the street-wise analysis revealed low epidemic risk (HI < 4% and BI < 5%) in Akbar Street, Ilango Adigal Street, Maraimalai Adigal Street, Mugambikai Kovil Street, Sivaji Street, Sri Krishna Street, and Venkateshwara Street. A moderate epidemic risk was observed in the remaining streets where HI ranged from 4% to 11.1% and/or BI ranged from 5% to 19.4%, with the highest BI recorded in Viyasar Street (19.4%). No street exhibited high-risk levels (HI > 35% or BI > 50%) during the survey. During the survey period (April–May 2024), two laboratory-confirmed dengue cases were reported from the study area, one each from Shivaji Street and Pandiyan Street. The limited number of reported cases during the study period corresponds with the low-to-moderate entomological indices observed. However, detailed prevalence data for the October–November 2023 period were not available at the time of writing, and therefore a direct comparison of dengue prevalence between the two periods could not be performed. From Figure 3, with respect to examination of the containers out of the 7140 containers inspected the predominant containers were found to be FP (3418), DPC (1637), coconut shells (412), DU (352), DD (172), earthen pot (270), GS (80), DT (76), DB (63), money plant (29), CT(16), fish tank (18), and drainage cap (1).

OPEN IN VIEWER

FIG. 3.

Type wise distribution of wet and dry containers inspected.

Among the wet containers inspected, the predominant wet containers were DPC (229), DU (143), FP (86) followed by DD (29), money plant (29), fish tank (10), coconut shell (7), and CT (5).

Thus, the higher percentage of dry containers in the study area gives the early warning that the dry containers may turn into ideal breeding sources soon after the water collection by the rain.

Discussion

The results of this study underscore the future risk associated with Ae. aegypti populations and their potential to transmit dengue fever. The present entomological survey assessed the abundance of Aedes immatures and dengue transmission risk in Pedhuchettipet ward, a known dengue hotspot within Lawspet constituency, Puducherry. The overall entomological indices indicated a low-to-moderate risk of dengue transmission, reflecting ongoing Ae. aegypti breeding activity in the area. The HI (3.6%) was below the epidemic threshold, whereas the BI (5.17%) and CI (4.36%) fell within the moderate-risk ranges (World Health Organization, 1972), suggesting the presence of sufficient breeding sites capable of sustaining vector populations under favorable environmental conditions. The occurrence of two confirmed dengue cases during the study period further supports the observed entomological risk levels.

The emergence of Ae. aegypti in all reared adults confirms its predominance as the primary dengue vector in the study area. The 60% adult emergence rate indicates that laboratory rearing conditions closely reflected field conditions, supporting the reliability of species identification and larval positivity results.

Street-wise analysis showed a heterogeneous distribution of vector breeding, with most streets exhibiting low risk and a few demonstrating moderate infestation. Viyasar Street recorded the highest BI (19.4%), indicating localized clustering of breeding sites. Although no street reached high-risk thresholds, the presence of multiple moderate-risk areas suggests potential escalation during the monsoon season without strengthened control measures.

Container analysis revealed that domestic containers such as FP, DPC, coconut shells, utensils, EP, and water-storage vessels within households were the predominant breeding sources. Semidomestic containers were less common. Among wet containers, DPC utensils, and FP were most frequently positive, highlighting poor storage and waste management practices. Additionally, many containers were dry at the time of inspection, representing latent breeding sites that could rapidly become productive following rainfall, particularly during the approaching monsoon season.

Continuous monitoring and proactive vector control measures are essential to prevent potential outbreaks, particularly given that only a few surveyed streets were free from dengue transmission risks. Future research should explore the ecological factors influencing Aedes populations further to inform more effective management strategies (Jeelani et al., 2015).

Additionally, it is recommended to conduct various vector control strategies in reducing the population of Ae. aegypti such as dengue source reduction and community-based interventions, public awareness campaigns, and the use of bio-larvicides may help in mitigating dengue transmission and enhancing public health outcomes. The use of Wolbachia-infected mosquitoes has also emerged as a promising biological control strategy, as Wolbachia can reduce the ability of Ae. aegypti to transmit DENV and thereby decrease dengue infection in human populations. ICMR–VCRC has initiated laboratory studies on Wolbachia spp-based vector control for prevention of dengue and chikungunya and the release of Wolbachia-transfected mosquitoes may be possible in the near future.

Implementing source reduction involves identifying and eliminating mosquito breeding sites, particularly in the domestic environment (Rahayu et al., 2019). This can include removing standing water from containers, cleaning gutters, and properly disposing of waste. By targeting these habitats, the reproductive capacity of Ae. aegypti can be significantly diminished, leading to lower mosquito populations and reduced transmission risk.

Thus, addressing the challenges posed by Ae. aegypti requires an integrated approach that combines environmental management, community education, and ongoing surveillance to effectively mitigate dengue transmission risks (Rahayu et al., 2019) in the Pedhuchettipet ward of Laswpet Constituency.

Conclusion

This study underscores the persistent risk of dengue transmission in Pedhuchettipet ward, Lawspet constituency, Puducherry, due to the presence of Ae. aegypti breeding sites. According to the WHO criteria for interpreting Stegomyia indices, the entomological indices recorded in this study site indicate a moderate risk of dengue transmission. This finding emphasizes the need for sustained and targeted vector control intervention. Integrated approaches, including community-based interventions, environmental management, and biological control strategies, are essential to mitigate the threat of dengue outbreaks. Strengthening public awareness campaigns and promoting source reduction practices can significantly limit mosquito proliferation. Continuous entomological surveillance is crucial to assess vector density trends and implement timely interventions, ultimately reducing the burden of dengue in the region.

Authors’ Contributions

Conceptualization, project administration, resources, facilitation of lab work, overall supervision of the work, review and editing of the –article: A.M.K. Field and laboratory work, data analysis, writing the –article: G.K.S.