Circulating dengue virus serotypes and vertical transmission in Aedes larvae during outbreak and inter-outbreak seasons in a high dengue risk area of Sri Lanka

Abstract

Background Spatial and temporal changes in the dengue incidence are associated with multiple factors, such as climate, immunity among a population against dengue viruses (DENV), circulating DENV serotypes and vertical transmission (VT) of DENV in an area at a given time. The level of VT in a specific location has epidemiological implications in terms of viral maintenance in vectors. Identification of the circulating DENV serotypes in both patients and Aedes mosquito larvae in an area may be useful for the early detection of outbreaks. We report here the results of a prospective descriptive study that was conducted to detect the levels of VT in Aedes mosquito larvae and circulating DENV serotypes in patients and Aedes mosquito larvae from December 2015 to March 2017 in an area of Sri Lanka at high risk for dengue. Methods A total of 200 patients with clinically suspected dengue who had been admitted to a tertiary care hospital during a dengue outbreak (3 study periods: December 2015–January 2016, June–August 2016, December 2016–January 2017) and in the inter-outbreak periods (February–May 2016 and September–November 2016) were investigated. Blood samples were drawn from the study participants to test for DENV. The houses of the study participants were visited within 7 days of admission to the hospital, and Aedes larvae were also collected within a radius of 400 m from the houses. The larvae were separately identified to species and then pooled according to each patient’s identification number. Patients’ sera and the Aedes larvae were tested to identify the infecting DENV serotypes using a reverse transcription PCR (RT-PCR) method. Levels of VT in Aedes mosquito larvae were also identified. Results All four DENV serotypes (DENV-1 to -4) were identified in the study area. In the early part of the study (December 2015–February 2016), DENV-3 was predominant and from April 2016 to March 2017, DENV-2 became the most predominant type. Four cases of DENV co-infections were noted during the study period in patients. Interestingly, all four DENV serotypes were detected in Aedes albopictus larvae, which was the prominent immature vectorial form identified throughout the study period in the area, showing 9.8% VT of DENV. With the exception of DENV-4, the other three DENV serotypes were identified in Aedes aegypti larvae with a VT of 8.1%. Conclusion Comparatively high rates of VT of DENV was detected in Ae. albopictus and Ae. aegypti larvae. A shift in the predominant DENV serotype with simultaneous circulation of all four DENV serotypes was identified in the study area from December 2015 to March 2017. Graphical Abstract

Potential Way to Develop Dengue Virus Detection in Aedes Larvae as an Alternative for Dengue Active Surveillance: A Literature Review

“…DENV detection was demonstrated in all three studies when testing larvae derived from laboratory-infected mosquitoes for virus detection. DENV also could be detected from filed-caught larvae in most studies (22/26) using various methods [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ]. Twenty-six studies used pooled immature specimens when detecting dengue virus.…”

Relationship between clinical and laboratory features with infecting dengue virus serotypes in a sample of dengue suspected adult patients from 2015-2017 in Sri Lanka

“…The proportion of infection with DENV-2 (n=14) followed by DENV-3 (n=13), DENV-1 (n=6) and DENV-4 (n=3) in our study sample reflects the epidemiology of dengue in Sri Lanka. In 2017 in the study area, DENV-2 was the main circulating serotype which resulted in the largest ever outbreak in the island [11] . Similar findings on circulating DENV serotypes have been reported in Malaysia [16] .…”

“…From 2012 to 2014, DENV-1 was the predominant serotype contributing to the outbreaks with lesser involvement of DENV-4 [3] . In 2017, the predominant circulating serotype was DENV-2, and this serotype contributed to the largest ever dengue outbreak recorded in Sri Lanka [11] .…”

Dengue Virus-2 Infection Affects Fecundity and Elicits Specific Transcriptional Changes in the Ovaries of Aedes aegypti Mosquitoes

“…Furthermore, other authors have suggested that mosquitoes serve as viral reservoirs due to their ability to transmit viruses to vertebrate hosts ( Wu et al, 2019 ). As an example, a study showed that the same DENV serotypes were detected circulating in wild-collected larva and patients’ serum during an outbreak in Sri Lanka ( Wijesinghe et al, 2021 ). After mosquitoes feed on a viremic host, the blood meal is processed in the mosquito midgut, where the virus will infect the midgut epithelial cells and start replicating ( Rückert and Ebel, 2018 ).…”