Determinants of urban mosquito population density and community responses: A cross-sectional study

Introduction

Vectors are defined as organisms that transmit infectious pathogens from humans to humans, or from animals to humans. Some of the most prevalent vector-borne diseases include malaria, filariasis, dengue, chikungunya, yellow fever, chagas disease, bubonic plague, and leishmaniasis are transmitted by arthropod vectors. These diseases contribute 17% of infectious diseases that affect the human population worldwide and cause approximately 7,00,000 deaths per year.¹

Mosquitoes are one of the most prominent arthropod vectors, representing a significant portion of the vector-borne disease burden, with over 80% of the global population are at risk.¹ Thes arthropods come under the class of Insecta, further classified into Anopheline and Culicine mosquitoes. Anophelines are responsible for transmitting malaria, which is known for their nocturnal biting habits and indoor resting behavior, as they typically bite between 10 PM and 4 AM and breed in clean sunlit water sources. India bears 79% of the global malaria burden.^2,3,4

Aedes aegypti and Aedes albopictus are mosquitoes that belong to the Culicines category, which are highly domesticated and commonly found near human dwellings that transmit dengue and chikungunya. They breed in water-filled containers in domestic and peri-domestic areas and bite especially during the day time and evening.⁵ Asia is home to 70% of the global dengue risk, with India being a significant contributor.^6,7 The first chikungunya outbreak occurred in the 1960s, followed by a period of dormancy until a major resurgence in 2006 affected 13 states in the country.^8,9

India’s vulnerability to mosquito-borne diseases is exacerbated by its eco-socio-demographic conditions, making them a major public health concern. Karnataka, a southern state in India, faces a significant burden of mosquito-borne diseases including malaria, dengue, lymphatic filariasis, and Japanese encephalitis. The prevalence of these diseases varies among districts. In 2010, the state recorded 1,09,118 malaria cases, with 28,065 attributed to Plasmodium falciparum.¹⁰

The coastal cities of Mangalore and Udupi together account for approximately 72% of the malaria cases reported in Karnataka.¹¹ In particular, Mangalore—a coastal town of Dakshina Kannada district with frequent heavy rainfall and high humidity—provides an ideal environment for mosquito proliferation. An initial survey conducted in Mangalore taluk identified 26 mosquito species across six genera. Mangalore and its surrounding areas are considered malaria-endemic, with an annual parasite index of 10–12.¹² Rapid urbanization in urban Mangalore, including extensive construction, inadequate drainage, and poor road conditions, has further contributed to the persistence of the endemic nature of mosquito-borne diseases in the area.¹³

This study aimed to explore the interactions between environmental, socioeconomic, and behavioral factors that influence vector presence in the study setting and community responses to vector-borne disease risks. These findings will help assess the level of vector nuisance, disease prevalence, and community engagement. By aligning with the Sustainable Development Goal 3.3—ending epidemics of malaria and other communicable diseases—the study’s results will focus on generating valuable evidence for urban vector control programs and the development of tailored community-based interventions.

Objectives

To identify the key determinants of mosquito presence in urban settings and assess community-measures taken to prevent an increase in mosquito density and control mosquito-borne diseases. Also to evaluate the community perceptions towards mosquito-borne diseases and quantify the disease burden from self-reported cases.

Review of literature

Various factors responsible for the rapid proliferation of mosquitoes in different regions of the world have been identified. A study conducted by (Wilke AB et al., 2020) in Miami-Dade Florida identified a few of the common aquatic habits which are responsible for harbouring 80% of all immature Ae. Aegypti and the proliferation increase in the presence of those aquatic habitats.¹⁴ Several studies have identified that Anopheles breeds in pools and streams, where people living in close proximity are at a high risk of malaria and its transmission.¹⁵ These studies have also identified malaria as a disease of the poor since they have less access to anti-mosquito measures, cannot afford preventive measures, and live in a mosquito-free environment with the contributing factor to this disease transmission as the age-old tradition of sleeping outside at night amid peak mosquito activity.

The use of preventive measures, such as effective lids over water storage containers and frequent emptying of containers, reduces the incidence of arthropod proliferation, especially Ae. Aegypti.¹⁶ There is a linear relationship among growing populations, rising socioeconomic status, and increased mosquito proliferation. Economically marginalized populations with high population density are particularly vulnerable to dengue disease burden.¹⁷ A different study employing logistic regression showed that tiled and concrete dwellings increased the likelihood of an area becoming a hotspot by 2.0 and 2.9 times, respectively, for dengue disease transmission.¹⁸

There is a significant relationship between rapid, unplanned urbanization and the proliferation of mosquitoes. One study revealed that inadequate urban infrastructure and sanitation play an important role in the transmission and reproduction of vectors, especially Aedes aegypti. These unplanned disorganized cities provide favorable conditions, such as artificial breeding grounds, presence of stagnant water, mosquito proliferation, and disease transmission.¹⁹ Climate change also has a huge impact on vector proliferation. It reduces larval development time and rapidly increases mosquito populations. It also leads to a reduction in the extrinsic incubation period by decreasing the time taken by the virus to reach the mosquito’s salivary glands, making it infectious.¹⁹

Knowledge regarding mosquito breeding sites, factors for mosquito proliferation, the impact of climate change, and urbanization on vector proliferation is essential to control rapid reproduction and increase mosquito population density. A study by (Garbin CA et al., 2021) revealed that 76% respondents believed that their neighborhood was likely to be infected by a disease spread by mosquitoes, but no action was taken by them, this concluded that there was a gap between the knowledge about the disease and the actions to be taken.²⁰ Another study by (Madeira NG et al., 2002) conducted on school children showed that after didactic intervention, knowledge about the proliferation of the vector increased leading to increased awareness, which was lacking prior to the intervention.²¹

Various determinants of mosquito proliferation have been identified across different studies, and the present study was conducted to identify such determinants in Mangalore and the measures taken by the community to prevent vector proliferation.

Methodology

This community-based cross-sectional study was conducted in Mangalore, a coastal city in the South Indian state of Karnataka, between September and October 2024, among Community households present in the urban field practice area of the Department of Community Medicine. The sample size was calculated based on a previous study conducted in Mangalore, Karnataka,²² it was reported that 83% of the people used preventive measures such as mosquito nets to prevent mosquito bite, using this as our anticipated proportion and 10% relative precision, 95% confidence interval, and adding 20% non-response rate as 95 sample size was calculated as follows:

N = Z α 2pq/d2: Z = 1.96, 95% confidence interval; p = 0.83; q = 1-p = 0.17, and d is 10% relative precision and 20% of non-response rate.

The study protocol was approved by the Institutional Ethics Committee, Kasturba Medical College Mangalore with No: IEC KMC MLR 09/2024/587, followed by permission from the Head of the Institute. The written consent was taken on an ‘Informed consent form’ which was provided to the participants ≥18 years of age for signature, and the participants <18 years of age were excluded from the study. All participants had the right to withdraw at any stage of the study, and all incomplete responses were considered withdrawal and excluded from the analysis. The study participants were approached from a household that was selected from five wards out of the total 60 wards present under the Mangalore City Corporation based on convenience; one reliable informant residing in the household for more than at least 1 year, who was aware of the household conditions and consented were included in the study, whereas temporary residents of less than a year, apartment complexes, and households without adult personnel were excluded.

The number of households to be taken for our study was divided equally among each ward; that is, a total of 19 households from each of the selected wards were considered for the study. A random street was selected from each ward and then, standing at the end of each randomly selected street, every 3^rd house present on the left side of the lane was considered for the study, which was continued in a clockwise order; in case of failure to meet the inclusion criteria, absence, or denial to take part in the study, the next house was considered. When the head of the household was absent during the time of data collection, information was collected from the oldest adult residing in the household. A pretested, semi-structured, internally validated physical questionnaire designed after extensive literature review was used for data collection, which comprised details such as sociodemographic data, mosquito proliferation and nuisance, determinants of mosquito breeding, behavioral and preventive measures, perception related to mosquito control, and self-reported cases of mosquito-borne diseases. Data were recorded after obtaining informed consent from the heads of the households.

The data collected were entered into MS Excel and analyzed using Jamovi version 2.6.26. Descriptive statistics are represented using frequencies and proportions. The association between two categorical variables was analyzed using the chi-square test, and a P value <0.05 indicates that there was a statistically significant association between the independent and dependent variables.

Results

Discussion

In the present study, 60% of participants reported experiencing moderate to severe mosquito nuisance in their locality over the past year. This contrasts with findings of Davidson et al., who noted that 80% of respondents in St. Johns County, Florida, felt bothered by mosquitoes daily or several times a week.²³ Notably, 71.5% of participants indicated that evenings were the peak time for mosquito activity, and 30.5% reported that mosquito bites disrupted their sleep. Additionally, 67.4% of participants described a moderate to severe presence of mosquitoes indoors, while 87.3% reported similar conditions outdoors. This is comparable to data from Kampango et al., which indicated an average of 85.93% An. gambiae s.l. bites per night, with 66% occurring indoors and 34% outdoors, peaking between 22:00 and 03:00 in a rural community in Chókwè District, southern Mozambique.²⁴

In the present study, 50% often found mosquitoes inside the house, whereas 48.3% of the population rarely found mosquitoes inside the house after the use of mosquito repellants or coils. 64.5% Of the population rarely found mosquitoes inside houses, whereas 32.8% often found mosquitoes inside houses after regular repairing or checking holes in window screens or mosquito nets. 61.2% Of the population rarely found mosquitoes inside houses without usage of insecticide sprays at home. 84.3% often found mosquitoes inside the house when they stored water in closed containers. Those who often repaired or checked holes in window screens and mosquito nets (p = 0.003) were more likely to report a lower presence of mosquitoes compared to those who rarely did the repair.

Considering the environmental factors, 69.4% of participants identified the rainy season as the period when mosquitoes were most prevalent. This aligns with a cross-sectional study by Mahgoub et al. in Barakat and El-Kareiba, Sudan, which found a high number of positive habitats during the rainy season, whereas the lowest numbers were reported during the hot followed by dry season.²⁵ The primary breeding sites identified in our study included water stagnation (74.7%), dense vegetation (54.7%), and nearby water bodies (20%). In contrast, Mahgoub et al. reported that the main breeding sites for various mosquitoes in Sudan were leaking water pipes (51.5%), followed by irrigation channels (34.2%), hoof prints (6.4%), tire tracks (5.5%), and water tanks (2.4%).²⁵ Water stagnation (p = 0.033) was significantly associated with a higher presence of mosquitoes, suggesting that stagnant water plays a crucial role in mosquito proliferation, and absence of construction (p value = 0.014) activity was significantly associated with a lower presence of mosquitoes, suggesting that presence of any type of construction activity can play a crucial role in mosquito proliferation.

Preventive measures among participants were notable as 91.5% used chemical repellents (insect sprays, vaporizers, smoke), 81% kept doors and windows closed, 55.7% utilized mosquito nets or screens, and 15.7% employed other specialized methods. This contrasts with a study in urban northern Gujarat by Mahalakshmi et al., which 67.3% used chemical measures as repellent creams or liquids, 22% used bed nets, and only 2% reported taking no precautionary measures.²⁶

In terms of community cleaning practices, 51.5% of individuals reported cleaning their surroundings daily, additionally, 38.9% checked water stagnation weekly; in contrast, 84.6% never reported water stagnation to authorities. Unfortunately, 58.9% indicated that municipal cleaning was infrequent in the locality. Notably, 25.2% regularly checked window screens or mosquito nets for damage and 50.5% stated that there had been no anti-fogging efforts by local authorities. This is compared with Mahalakshmi et al.’s findings in northern Gujarat, where 88% cleaned their homes daily, 57.3% cleaned their surroundings weekly, and 82% actively avoided water stagnation.²⁶

In the present study, 29.4% of participants reported suffering from a mosquito-borne disease in the past year, with dengue accounting for 71.4% of cases. Common symptoms included fever (96.4%), headache (78.5%), joint pain (60.7%), and muscle pain (46.4%), 82% sought treatment at private clinics. This aligns with findings from a study conducted by Kumar et al. in a tertiary hospital in Udupi district, which indicated that 83.9% of cases were due to dengue fever, presenting symptoms such as fever (99.1%), myalgia (64.6%), vomiting (47.6%), headache (47.6%), abdominal pain (37.5%), and breathlessness (17.8%).²⁷

Finally, 92.3% of participants in our study reported experiencing complications post-recovery, primarily weakness, while 7.6% experienced cold, leg pain, headache, or eye pain. This contrasts with a study in Vietnam by Tam et al., who reported that 12.5% of participants experienced alopecia, 11.1% had blurred vision, 9.5% faced concentration difficulties, and 8.5% suffered from fatigue following dengue infection.²⁸

The study found that 82.1% of the population perceives water stagnation (p = 0.003) as a significant factor in mosquito proliferation, indicating it is a major factor in the prevalence of mosquito-borne diseases. Construction sites, water bodies, dense vegetation, and water storage in open containers were identified as the significant determinants. Additionally, 17.8% of individuals perceive water leakage from tanks and taps (p = 0.032) as a key determinant, indicating that water leakage from household stores is a significant factor in the prevalence of mosquito-borne diseases. Overall, these factors contribute to the prevalence of mosquito-borne disease.

Conclusion

In conclusion, knowledge and attitudes regarding mosquito borne diseases in the community are apt and good. It correlates with good practice but only to a certain extent. Practicing the basic requirements, for example, using mosquito sprays and closing windows, is to par. However, proper intervention by local authority is necessary to combat the main factors responsible for mosquito breeding, such as water stagnation and the presence of dense vegetation. This proves the presence of gaps identified by our study, where despite most people being aware of mosquito-borne diseases, respondents recognized the lack of awareness and good preventive practices. Hence, apart from awareness, there is a dire need to provide the right personnel and services to combat mosquito-borne diseases.

Recommendation

Ethical approval

The study protocol was approved by the Institutional Ethics Committee, Kasturba Medical College Mangalore with No: IEC KMC MLR 09/2024/587, followed by permission from the Head of the Institute. The written consent was taken on an ‘Informed consent form’ which was provided to the participants ≥18 years of age for signature, and the participants <18 years of age were excluded from the study. All participants had the right to withdraw at any stage of the study, and all incomplete responses were considered withdrawal and excluded from the analysis.