Co-infection of Aeromonas veronii and Megasporoporia sp. associated with mass mortality in Labeo bata: pathological effects and immune modulation in the host.

Co-infections have a considerable influence on fish production, altering the progression and severity of various fish diseases. Despite this, the impact of co-infection on aquatic animals, including fish, has only recently received minimal attention, leaving a significant gap in research. The research examines the cause behind significant mortality in Labeo bata. Microbial pathogens were isolated from infected tissue samples of bata, with preliminary identification of the strains as Aeromonas veronii and Megasporoporia sp. This identification was based on morphology, 16S rRNA and ITS PCR sequencing, along with phylogenetic analysis. A co-infection fish model was developed to explore the cellular and molecular responses of fish amidst bacterial and fungal co-infection scenarios. Additional analysis suggested that the co-infection condition may be linked to the outbreak of the disease and the resulting mortality of L. bata, as confirmed by survival assays, histological examinations, and qPCR analysis. The findings indicated that co-infection with A. veronii and Megasporoporia sp. resulted in different degrees of cellular alterations within the muscle tissues of infected L. bata samples. Transcription analysis further reveals that co-infection influences the expression of genes associated with inflammation (TNF-α, IL-1β, iNOS), immune activation (TLR 4, C3, MYD88, NOD 1), and both innate and adaptive immune responses (IFN-γ, Hsp70, Mx, IgM) in liver, kidney, and gill tissues from infected L. bata. The insights gained from this study are invaluable for understanding co-infection dynamics and pathobiology, which are essential for risk assessment and the development of management strategies to mitigate virulence.