INTRODUCTION

Vector-borne diseases are illnesses transmitted to humans by insects or other organisms. Their impact causes substantial morbidity and economic repercussions across affected communities worldwide. These illnesses, constituting 17% of the global infectious disease burden, are most prevalent in impoverished tropical and sub-tropical regions with limited access to clean water and sanitation (25). In Costa Rica, public health is detrimentally affected by several arboviruses and neglected tropical diseases transmitted by vectors. In rural areas, including Cuajiniquil, vector-borne diseases are underresearched, leading to deficits in understanding ways to prevent, mitigate, and care for those infected. 

Mosquitoes play a prominent role in transmitting diseases within Cuajiniquil. Several arboviruses have been reported in the region, including Dengue Fever (DENV), Zika Virus (ZIKV), West Nile Virus (WNV), and Saint Louis Encephalitis Virus (SLEV). Among the mosquito species populating the country, the Aedes genus has been found to transmit these diseases primarily to humans. However, DENV is the most prevalent mosquito-borne pathogen in the country and the world's fastest-growing vector-borne disease, with a 30-fold increase in incidence over the last 50 years (22, 25). Research has shown that Dengue outbreaks strain hospitals, leading to prolonged wait times, a scarcity of essential health resources and personnel, and substantial financial burdens on low-income households (13). Although there are existing studies of mosquitoes in Cuajiniquil, limited data focuses on the Aedes genus and their impact on public health (1). The recurring Dengue outbreaks in Cuajiniquil underscore the need to improve the current understanding of Aedes mosquito density to tailor effective preventative strategies for the community. 

Costa Rica also hosts the disease vector for Chagas disease. This neglected tropical disease is transmitted through contact with the feces of an infected T. dimidiata, commonly known as the "kissing bug." The parasite, T. cruzi, infects the host's body when the insect bites exposed skin and defecates over the bite site (15). Patients with Chagas disease may progress to develop Chronic Chagas Cardiomyopathy (CCC), where 20-40% of cases result in sudden fatality from cardiac arrest (6). Chagas disease, estimated to infect six to eight million individuals worldwide, is the cause of death of 50,000 people annually; however, the true impact may be greater due to restricted testing access and the potential for underreporting (19, 20). In more developed areas like San José, Costa Rica, advanced technological resources and a well-equipped healthcare system enable effective disease surveillance and timely identification (17). In contrast, less developed regions, like Cuajiniquil, are challenged with limited healthcare access and a lack of patient education. This results in an incomplete understanding of the current state of Chagas disease in Cuajiniquil. 

The healthcare infrastructure in Cuajiniquil faces significant challenges in dealing with vector-borne diseases. Due to Cuajniquil’s rural setting, limited access to healthcare services impedes timely medical attention during disease outbreaks. Without effective preventative measures to reduce the impact of these outbreaks, the local healthcare system becomes strained, with the number of patients exceeding the availability of medical resources. The lack of health education programs also contributes to insufficient community awareness about disease symptoms and prevention measures, leading to increased disease transmission rates. 

Understanding vector-borne diseases like Dengue and Chagas disease in Cuajiniquil is pivotal for shaping effective public health strategies against these illnesses. In this study, two questions were addressed: What is the population proportion of Aedes mosquitoes, and what is the prevalence of Chagas disease in Cuajiniquil? The population proportion of Aedes mosquitoes signifies the potential for disease transmission, as higher mosquito density often correlates with an increased risk of infection (20). Determining the prevalence of Chagas disease through infected T. dimidiata represents the likelihood of human exposure and infection. The implications of this research will assist in creating public health strategies in Cuajiniquil and provide valuable data to the global understanding of Dengue and Chagas disease transmission.

Materials and Methods

Assessing Aedes Mosquito Population Proportion

Mosquitoes were captured in three distinct locations of Barrio Cuajniquil: The mangroves, Casa Verde, and Restaurant Arrecife. These locations were selected due to their unique attributes and variations in human activity. The mangroves were characterized by large bodies of stagnant salt and rainwater, rich biodiversity, and limited human presence. Casa Verde represented the epicenter of Barrio Cuajiniquil, and Restaurant Arrecife was chosen for its high amount of human activity. Each location underwent extensive surveys for seven days during the morning, afternoon, and evening hours. Apart from these locations, mosquitoes incidentally captured at the Dive Center and private residences were also included in the study. 

Mosquitoes were captured using a spray bottle containing water and soap, a plastic bag, and tweezers. Upon sighting a mosquito, the spray bottle was used to immobilize it and ensure minimal physical damage. Tweezers were used to transfer the mosquito into a plastic bag. The bags were then stored in a freezer and labeled with the date, time, and location of capture. Before being placed under a dissecting microscope, the specimens were treated with ethyl alcohol and placed into a petri dish. If applicable, the Aedes genus and species were identified using published keys (18, 11).

Assessing the prevalence of Chagas disease

Throughout seven days, nine individuals searched for T. dimidiata in more than 15 locations. Approximately 45 hours of human effort were invested in this endeavor. The searches covered one private farm, one abandoned farm with a high presence of bats and small rodents, ten households with livestock, and the local supermarket's vicinity. These locations were intensively searched for an average of 3 hours per location. Upon encountering stacks of dry wood, some consisting of more than 30 individual pieces, each piece was meticulously inspected. Thorough searches were conducted on animal cages' roofs, undersides, interiors, and exteriors. Based on the results of previous studies on Chagas disease in Monteverde, Costa Rica, searching chicken coops was emphasized (23). The inside of homes was also examined when permitted, including the underside of bedframes and tables. 

The feces of T. dimidiata were examined under a compound microscope to determine the presence of T. cruzi. The insect was laid supine on a glass slide, and a blunt metal probe was applied to the ventral abdomen. A downward motion towards the posterior abdomen was repeated until a fecal sample was collected. One drop of salt and water solution was added to the fecal sample to ensure any T. cruzi present would not dry up before being discovered. A glass coverslip was carefully placed over the fecal sample, and the slide was observed under the microscope at 1000 power using oil immersion. The presence of the T. cruzi parasite was observed by its distinctly long and narrow flagella, which facilitates its movement.

RESULTS

Population proportion of Aedes mosquitoes

Among the 117 mosquitoes captured, 26 (22.22%) were classified within the Aedes genus. Four of these were identified at the species level as Aedes albopictus, a primary transmitter of dengue disease (17). Within this group, the gender distribution revealed that 54.55% were female, 13.64% were male, and 31.82% were undetermined. This is crucial as only female mosquitoes can transmit disease, as they require blood meals to make eggs (14). 

Casa Verde was found to be the location with the highest proportion (40%) of Aedes mosquitoes, most prevalent during late afternoons (5:30-6:30 PM) and mornings (9-10 AM). The Mangroves also displayed significant Aedes activity (36%), with most captures occurring late afternoon (5:30-6:30 PM). No Aedes mosquitoes were found at Restaurant Arrecife, even though the majority of mosquitoes, 61 individuals (52.13%), were captured there. No Aedes mosquitoes were observed after 6:30 PM, aligning with the consensus that these mosquitoes are primarily active during day (5) (Figures 1 and 2).

 Among the 18 female Aedes mosquitoes found, eight were identified at Casa Verde during two time frames: 9-10 AM and 5:30-6:30 PM. Six were observed in the mangroves during the 5:30-6:30 PM interval, with an additional 3 discovered in the area between 1:30- 3 PM. All four Aedes albopictus were female, with two found at the mangroves and two at Casa Verde. 

This data shows an association between the time of day when mosquitoes were collected—search hours spanning from 6 AM to 10 PM—and the presence of Aedes mosquitos (chi-square is 21.2743, p=0.000024). Aedes mosquitos are more prevalent during the day and dusk and rarely occur at night (Figure 4).

Assessing Chagas Disease Prevalence

After the seven-day investigation spanning 15 locations, one adult T. dimidiata was captured in close proximity to the local supermarket. It was discovered outdoors between 1 and 3 PM, approximately ten yards from the supermarket entrance. The predominant animals in the vicinity were stray dogs and cats. The specimen appeared engorged, suggesting a recent blood meal. Upon laboratory examination, the T. dimidiata revealed the presence of T. cruzi under oil immersion at 1000x magnification. The Trypanosomes observed were in epimastigote form, where the flagellum was partially connected to the cell body. These findings suggest that the prevalence of Chagas disease as a vector-borne ailment may not be as pronounced in Cuajiniquil when compared to other areas of Costa Rica. However, the detection of T. cruzi in the discovered T. dimidiata underscores the continued existence of the disease-causing agent.

DISCUSSION

Public Health Approaches for Preventing the Spread of Dengue

The dataset on the Aedes mosquito population provides insights for creating tailored Dengue prevention strategies in Cuajiniquil. Identifying 26 Aedes mosquitoes, including Aedes albopictus, emphasizes the need for continued vector surveillance. Houses in Barrio Cuajiniquil near Casa Verde and the Mangroves, which exhibit higher proportions of Aedes mosquitoes, demand immediate attention control measures. Despite Restaurant Arrecife showing no Aedes presence, its status as a significant mosquito capture site (61 individuals, 52.13%) necessitates continuous monitoring and potential preventive measures to sustain this absence. 

Education campaigns targeting Aedes mosquitoes should be established within the Cuajiniquil community. Programs focusing on Aedes mosquito behaviors, particularly their peak activity times and breeding sites, can significantly enhance residents’ awareness of when Dengue transmission risks are highest and when preventive measures should be employed. Based on the results of this data, Aedes mosquitos are most prevalent between 9-10 AM and 5:30-6:30 PM. During these times, residents should practice personal protective measures, such as wearing long clothing and using mosquito repellents. 

The heightened prevalence of Aedes mosquitoes near Casa Verde may be attributed to the abundance of breeding sites in this area. Thorough observations revealed significant water accumulation in various containers left in streets and front yards, such as tires, pots, and coconuts. Similarly, abandoned boats filled with rainwater in the Mangroves may also contribute to the increased concentration of Aedes mosquitoes in the area. Based on the results of this study, Cuajiniquil residents should be educated through public health campaigns on the nature of these breeding sites and their role in mosquito proliferation, emphasizing the urgent need for their elimination.

 Despite no Aedes mosquitoes being detected during nighttime surveillance, using a mosquito net while sleeping remains imperative as a preventive measure. Data analysis revealed that 52.3% of the captured mosquitoes were active at night, indicating a high prevalence of mosquito activity during this time. More extensive research could reveal a greater incidence of Aedes mosquitoes prevalence after dark. Recent studies have also highlighted Aedes mosquitoes' attraction to artificial light at night (10). Therefore, despite the apparent absence of Aedes mosquitoes during this time, adopting protective measures remains crucial to mitigate the risk of Dengue and other diseases carried by Aedes that have been reported in the area (13). 

It is crucial to recognize that the socio-economic status of Cuajiniquil residents could hinder their access to mosquito-prevention resources. Evidence indicates a correlation between dengue and poverty (4), suggesting that frequently purchasing mosquito repellents is not sustainable for low-income households. Mosquito nets may also be unavailable at local stores or financially out of reach for Cuajiniquil residents. Government initiatives can ensure broader access to preventive measures for all residents, irrespective of their socio-economic status. This approach becomes pivotal in ensuring equitable access to mosquito-prevention resources in Cuajiniquil. 

Public Health Approaches for Preventing Chagas Disease 

The results of this study reveal that Cuajiniquil exhibits a scarce population of T. dimidiata, suggesting a low risk of Chagas disease transmission; however, implementing public health strategies remains vital due to the presence of T. cruzi, the disease-causing agent. Extensive research over a longer period and during Costa Rica’s dry season could uncover higher occurrences of T. dimidiata in Cuajiniquil. Therefore, educating residents on identifying these insects and recognizing their habitats, such as underneath beds, chicken coops, and among dry wood, is pivotal for effective disease control. Public health efforts should also encompass an understanding of the behavioral patterns of T. dimidiata. This species conceals itself during the daytime and actively seeks out humans and animals at night. Therefore, it is imperative that individuals at risk for Chagas disease utilize bed nets during sleep. Educating individuals about these behavioral traits is essential to enhance their awareness of when they are most susceptible to Chagas disease transmission (24). It is also imperative that the closest treatment facilities are well known, as timely access to treatment will increase medication efficacy (7).

ACKNOWLEDGMENTS

I sincerely thank my primary advisor, Frank Joyce, and my secondary advisor, Federico Chinchilla, for their invaluable guidance and support. I also express my gratitude to my peers and the residents of Cuajiniquil who assisted me in my mosquito-catching and Chagas bug-hunting efforts.