Infection Dynamics And Shedding Kinetics Of Nervous Necrosis Virus In Juvenile Seven Band Grouper Using An Intraperitoneal Infection-Cohabitation Model

Nervous necrosis virus (NNV) affects more than 177 species of cultured fish including seven band grouper. The present study evaluated the shedding and transmission kinetics of NNV in seven band groupers using a cohabitation challenge model. Initial infection studied by intraperitoneal (IP) injection showed shedding of NNV was acute and peaked within 3-5 days after exposure. This was followed by a post peak period of diminished viral shedding and afterwards an increase in shedding was noticed at 12-16 days in half of the infected fish. In the cohabitation challenge viral shedders used at 10%, 30%, and 50% yielded 20%, 30%, and 100% mortality respectively in naive fish while within-host viral load during the onset of mortality did not show any significant difference across the groups. Peak viral shedding rate was 5.76 x 10(5) TCID50/L in the 10% shedder group. The other two groups shed at significantly higher than the 10% group with similar rates: 5.82 x 10(6) TCID50/L in the 30% and 6.1 x 10(6) TCID50/L in the 50% shedder groups. The empirically derived lowest effective infectious dose of NNV for the bath challenge was 10(5) TCID50/L. The observations from the present study provide an understanding of NNV shedding kinetics and its transmissibility that assist in better decision making in management of VNN outbreaks.