Public health concerns: Assessment of synanthropic status and sanitary risks of muscid flies (Insecta: Diptera) from wet market areas of Kolkata Metropolitan Area, West Bengal, India

Introduction: Determination of the synanthropic index is essential for assessing the degree of association between species, in this case, necrophagous dipterans, and humans; thus, knowledge of synanthropic relationships is crucial not only from the perspective of animal ecology and behavior but also from the standpoint of human health and hygiene.

Methods: This study aimed to detect muscid flies with the highest synanthropy and relative abundance in and around the open wet markets of the Kolkata Metropolitan Area (KMA), along with their potential risk to human health and hygiene as potential carriers of pathogenic bacteria. Furthermore, pathogenic bacteria on both the external body surface and within the gut of the most abundant eusynanthropic muscid species were assessed, highlighting potential sanitary and hygiene concerns. To detect communities of bacteria, amplicon sequencing of the V3-V4 hypervariable region (16S rDNA) was performed using the Illumina (NOVASEQ 6000) platform.

Results: The experiment was conducted from 2022 to 2023 in twelve study sites involving four municipalities. A total of 4669 muscid flies representing seven genera and thirteen species were collected using baited traps. Differences in flies’ abundance were evident across different environments. Musca domestica and Musca sorbens were the prevailing muscid species in urban and rural wet markets, with relative abundance values of 57.57 and 18.05, respectively. Musca domestica was also the most dominant fly in all of the three environments. Principal Component Analysis (PCA) indicated a robust connection between Musca domestica and urban wet markets, as evidenced by the highest synanthropic index (+91.14). Pathogenic bacterial genera like Vibrio, Aeromonas, Enterobacter, Vagococcus, Proteus, Escherichia-Shigella, Pseudomonas, Acinetobacter, Klebsiella, Morganella, etc., were identified from both the external body surface and gut of Musca domestica.

Conclusion: These results regarding muscid flies describe their role as potential vectors and can aid in assessing proper sanitation and promoting better control strategies instead of eradicating the whole fly community.