Portal Entry and Progression of Betanoda Virus Causing Viral Nervous Necrosis in Sevenband Grouper <i>Epinephelus septemfaciatus</i>

Abstract

A study was conducted to  identify the entry site for the betanodavirus, the causative agent of viral nervous necrosis (VNN) in 375 fish (150 spawn, 150 fry and 75 fingerling) during the period from March to August 2003. Highly susceptible fish, sevenband grouper Epinephelus septemfasciatus to sevenband grouper nervous necrosis virus (SGNNV) was used as experimental fish. Fish were placed into the seawater containing 10⁴ TCID₅₀ mL^-1 of the viral isolate for 1 h. Samples for virus isolation were randomly collected at an interval of 3 h, 12 h, 24 h and daily, and continued until 5 to14  days depending on the mortality. The inoculated virus could first recover from the mouth including nostril at 3 h of exposure and then from fin at 12 h, and within 1 d it was detected from all the organs examined at titers ranging from 10⁴ to 10⁷ TCID₅₀ g^-1. The highest titer was found at day 5 in the target organs of central nervous system (CNS), i.e., the brain, bone including spinal cord, and eye. The results suggest that nasal route the initial route for the portal entry of betanodavirus into fish.

Key words: Betanodavirus; viral nervous necrosis; virus titration; portal entry, nasal route; sevenband grouper

doi: 10.3329/bjvm.v2i1.1942

Bangl. J. Vet. Med. (2004). 2 (1) : 83-87