Complex relationships between Aedes vectors, socio-economics and dengue transmission—Lessons learned from a case-control study in northeastern Thailand

Abstract

Background/Objectives Dengue fever is an important public health concern in most tropical and subtropical countries, and its prevention and control rest on vector surveillance and control. However, many aspects of dengue epidemiology remain unclear; in particular, the relationship between Aedes vector abundance and dengue transmission risk. This study aims to identify entomological and immunological indices capable of discriminating between dengue case and control (non-case) houses, based on the assessment of candidate indices, as well as individual and household characteristics, as potential risk factors for acquiring dengue infection. Methods This prospective, hospital-based, case-control study was conducted in northeastern Thailand between June 2016 and August 2019. Immature and adult stage Aedes were collected at the houses of case and control patients, recruited from district hospitals, and at patients’ neighboring houses. Blood samples were tested by RDT and PCR to detect dengue cases, and were processed with the Nterm-34 kDa salivary peptide to measure the human immune response to Aedes bites. Socioeconomic status, and other individual and household characteristics were analyzed as potential risk factors for dengue. Results Study findings showed complex relationships between entomological indices and dengue risk. The presence of DENV-infected Aed es at the patient house was associated with 4.2-fold higher odds of dengue. On the other hand, Aedes presence (irrespective of infectious status) in the patient’s house was negatively associated with dengue. In addition, the human immune response to Aedes bites, was higher in control than in case patients and Aedes adult abundance and immature indices were higher in control than in case houses at the household and the neighboring level. Multivariable analysis showed that children aged 10–14 years old and those aged 15–25 years old had respectively 4.5-fold and 2.9-fold higher odds of dengue infection than those older than 25 years. Conclusion DENV infection in female Aedes at the house level was positively associated with dengue infection, while adult Aedes presence in the household was negatively associated. This study highlights the potential benefit of monitoring dengue viruses in Aedes vectors. Our findings suggest that monitoring the presence of DENV-infected Aedes mosquitoes could be a better indicator of dengue risk than the traditional immature entomological indices.

Serological biomarker for assessing human exposure to Aedes mosquito bites during a randomized vector control intervention trial in northeastern Thailand

“…This study showed that the human-mosquito contact is influenced by human behavioral characteristics, socio-demographic conditions, climatic factors, and trial vector control interventions associated with dengue transmission risk as previously demonstrated [ 8 , 19 , 56 ]. The relationship between human dengue infections and the intensity of the human-antibody response to Aedes bites could not be ascertained because incident dengue cases were not detected in the study participants during the time of longitudinal follow-up.…”

“…Further analysis is on-going to confirm the observation of the apparent lack (or very low) transmission during the study period (to be reported elsewhere). In a recent case-control study conducted in northeastern Thailand (conducted by this study team), neither the adult mosquito abundance at the household level nor the degree of human exposure to Aedes bites was correlated with a higher odds of acquiring dengue infection [ 56 ]. Although consistent with some previous results in Southeast Asia [ 43 , 56 ], the small sample size of DENV-positive Aedes might explain the lack of significance between the human- Aedes exposure and the risk of DENV infected bites seen in this study.…”

“…The specific human IgG response to the Aedes Nterm-34kDa salivary peptide (Genepep, Saint Jean de Védas, France) was measured by an enzyme-linked immunosorbent assay (ELISA) as described previously [ 48 , 56 ]. This secreted salivary peptide was selected because it exhibits high antigenic properties and it is specific to Aedes genus, therefore allowing to specifically measure the immune response to Aedes bites alone [ 42 ].…”

Ecological, Social, and Other Environmental Determinants of Dengue Vector Abundance in Urban and Rural Areas of Northeastern Thailand

“…Ae. aegypti is the main dengue vector in Thailand and is well-adapted to human dwellings and their immediate surroundings [ 47 ]. The abundance of adult and immature Ae.…”

“…However, evidence about the accuracy of the PCI has been mixed [ 41 ]. Household construction may play a role in vector abundance and DENV transmission risk; a previous study found greater risk for contracting dengue among people living in two-floor houses in northeastern Thailand [ 47 ]. Interestingly, no such association was found in our study ( Table 4 ), except for significant associations of windows screened with netting and home wall types (wood/cement/bricks) with the abundance of adult female and immature Ae.…”