Environmental variability and pathogen synergy influencing tilapia lake virus outbreaks on tilapia farms in Tamil Nadu, India.

Tilapia lake virus (TiLV) has emerged as one of the important viral pathogens affecting wild and farmed tilapia worldwide. In this study, we investigated the prevalence of TiLV and its association with coinfections and environmental parameters (pH, temperature, ammonia, and nitrite) on tilapia farms around Tamil Nadu, India. Principal component analysis (PCA) was used to analyse the associations between variables by assigning severity scores (0, 1, 2). The PCA results identified lower temperatures during the northeast monsoon as a key driver of TiLV outbreaks, along with coinfections with bacteria such as Aeromonas veronii, Streptococcus agalactiae, and Enterococcus sp., which exacerbate disease severity. Histopathological examination revealed prominent syncytial giant cells and tissue necrosis in TiLV-infected fish. The outbreaks were most frequent at water temperatures around 20–21°C, coinciding with sudden rainfall and temperature drops in the infected regions. These findings emphasize the importance of understanding environmental factors and coinfections to improve disease management strategies and mitigate the impact of TiLV on tilapia farming in Tamil Nadu, India.