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Diseases of Aquatic Organisms

    DAO prepress abstract   -  DOI: https://doi.org/10.3354/dao03638

    Co-infection of Lactococcus garvieae and Tilapia lake virus (TiLV) in Nile tilapia Oreochromis niloticus cultured in India

    Thangaraj Raja Swaminathan*, Sundar Raj Nithyanantham, Lekshmi Narendrakumar, Arathi Dharmaratnam, Neeraj Sood, Pravata Kumar Pradhan, Krupesha Sharma S. R. , Kuldeep Kumar Lal

    *Corresponding author:

    ABSTRACT: Tilapia lake virus (TiLV) and Lactococcus garvieae are two major pathogens of cultured Nile tilapia Oreochromis niloticus. In June–July 2018, a disease outbreak was reported in Nile tilapia cultured in brackish water floating cages in Kerala, India. Affected fish died gradually and cumulative mortality reached ~75% within 1 mo. In the present study, TiLV and L. garvieae were isolated from the infected fish and confirmed. The nucleotide analysis of the partial sequence of segment 3 revealed that the present TiLV isolate showed 100% similarity with TiLV MF574205 and 97.65% similarity with TiLV KU552135 isolated in Israel. Partial 16S rDNA nucleotide sequence of L. garvieae shared 99% similarity with the 16S rDNA nucleotide sequence of L. garvieae isolated from Nile tilapia in Brazil. Eight virulence genes (hly-1, 2, 3, NADH oxidase, adhPav, LPxTG-1, LPxTG-4, adhC1) were amplified in the present isolate. In the experimental challenge study, the onset of mortality started earlier in fish co-infected with TiLV and L. garvieae (3 days post-infection [dpi]) when compared to other groups. The cumulative mortality (90% at 12 dpi) was significantly higher in the co-infected group than in fish infected with TiLV (60% at 12 dpi) and L. garvieae (40% at 12 dpi) alone. This study reveals that synergistic co-infection of TiLV and other bacteria may aggravate the mortality in disease outbreaks. To the best of our knowledge, this is the first report of co-infection of L. garvieae with TiLV associated with mass mortality in Nile tilapia in India.