Tilapia lake virus infection disrupts the gut microbiota of red hybrid tilapia (Oreochromis spp.)

Viral infections have the potential to damage fish intestines and disrupt the composition and diversity of the bacterial populations. In this study, we investigated the gut microbiota profiles of 23 red hybrid tilapia (10 +/- 3 g) infected with Tilapia lake virus (TiLV) via two different methods. For the intraperitoneal (IP)-injection, 50 mu l of TiLV at a concentration of 105 TCID50/ml was administered into the fish's coelomic cavity. In the cohabitation challenge method, infection was achieved by injecting the virus into the coelomic cavity of the inducer fish and allow them to cohabited with cohabitation fish at a ratio of 1:3. The cohabitation infected fish had a cumulative mortality rate of 49%, while the IP-injection group had 81.5%, which was accompanied by clinical signs, severe histopathological changes in the intestines and high viral loads in the intestines over the infection period at 6, 12 and 21 days post challenge (dpc). Most importantly, an analysis of the bacterial populations based on the alpha and beta diversity patterns revealed distinct alterations in the intestines of the fish infected via IP injection and cohabitation and the control fish. Specifically, our findings highlighted a reduction in Cetobacterium (phylum Fusobacterium) and an increase in Brevinema (phylum Spirochaetes) in the infected fish at 6 and 12 dpc. Indeed, the elevation of Brevinema population is associated with a higher mortality rate within the IP-injection compared to the cohabitation group. Remarkably, the fish that survived TiLV infection at 21 dpc showed a higher abundance of Bacillus (phylum Firmicutes), which was in contrast to that at earlier time points (6 and 12 dpc). While Brevinema has been recognised as a potentially opportunistic pathogen in fish, different strains of Bacillus are commonly used as probiotics to promote fish health and enhance disease resistance. Our findings thus provide valuable insights into the distinct shifts occurring within fish gut microbiota during TiLV infection and suggest potential implications for improving gut health and resistance to viral infections in tilapia. Taken together, our study establishes that TiLV infection triggers significant changes in the diversity and composition of the intestinal microbiota in red hybrid tilapia.