Appendix I - SUPPLEMENT - Number 5
TITLE: Herpesvirus salmonis Type 2
INTRODUCTION: Herpesvirus disease of salmonids, Herpesvirus salmonis Type 2, previously the oncogenic viruses Oncorhynchus masou virus (OMV) and H-83, yamame tumor virus (YTV), coho salmon tumor viruses (CSTV, OKV, COTV, CSLV) and the nononcogenic Nerka virus from Towda Lake, Akita and Amori Prefecture (neVTA). Herpesvirus salmonis Type 2 causes mortality in salmon fry and induces tumors in survivors. Experimental infections have been demonstrated in rainbow trout and chum salmon, kokanee, and coho salmon.
KNOWN GEOGRAPHIC RANGE: Japan.
INSPECTION REQUIREMENT: Inspection for Herpesvirus salmonis Type 2 shall be required
only if the fish/gametes originate from Japan.
Clinical signs include:
1) First isolated in ovarian fluids of masou salmon with no abnormal external signs;
2) Pathogenic to fry;
3) Fish older than two-hundred forty (240) days appear to be resistant;
4) Affected fish are lethargic or show erratic swimming behavior, anorexic, display exophthalmia and petechiation of the body surface, particularly under the jaw; and
5) Tumors may occur in the mouth, head and fin regions of surviving fish beginning one-hundred thirty (130) days post-infection.
DIAGNOSIS:
1. Typical CPE in susceptible cell cultures (RTG2 and CHSE-214) at 15°C: massive syncytium and formation of multinucleate giant cells.
2. Histopathology: kidney of one (1) month old salmon show typical syncytium formation with accompanying necrosis of hematopoietic tissue; epidermal cells of the mouth, jaw, operculum or skeletal tissues may show necrosis and numerous granules; atrophy and necrosis of the liver may occur; necrosis of the pancreas and spleen may be observed in moribund specimens.
3. Confirmatory diagnosis: neutralization with specific anti-OMV, YTV, or CSTV serum.
DETECTING SUBCLINICAL INFECTIONS:
1. The presence of tumors with serum anti-OMV titers is indicative of prior exposure to OMV.
TRANSPORTATION AND STORAGE OF SAMPLES:
1. Samples shall be frozen for not more than seven (7) days.
2. Ideally, samples shall be transported on ice and processed within twenty-four (24) hours.