ABSTRACT: A syncytium-inducing viral agent was initially isolated from the ovarian fluid of a domestic white sturgeon Acipensertransmontanus female using the sturgeon spleen cell line WSS-2. Examination of infected cells by transmission electron microscopy revealed ultrastructural characteristics typical of the Herpesviridae. On the basis of differences shown by comparative invitro growth studies and serological assays, the new adult isolate was tentatively designated WSHV-2 to distinguish it from a previously reported herpesvirus from juvenile white sturgeon, WSHV (WSHV-1). A water-borne transmission trial at 3 virus concentrations was conducted to determine the susceptibility of juvenile sturgeon to the newly isolated virus. At virus doses of 10⁵ and 10⁴ TCID₅₀ ml^-1 cumulative mortality reached 80% within 6 wk at a water temperature of 17*C. Virus was reisolated from all mortalities with concentrations approaching 10⁷ TCID₅₀ g^-1 in cutaneous epithelial tissues where severe hyperplastic lesions were observed. Challenge with 10³ TCID₅₀ ml^-1 of WSHV-2 failed to induce clinical signs or mortality, although chronic subclinical infections were detected in a majority of survivors 70 d post-challenge. During our investigations of WSHV-2 from adult sturgeon, a second virus isolation was obtained from ulcerative skin lesions of naturally infected subadult white sturgeon. This virus induced identical cytopathic effects in WSS-2 cells to that caused by the adult isolate from ovarian fluid. Serum anti-WSHV-2 neutralizing activity was detected in subadults with skin lesions and among fish recovering from these lesions. Serum from naturally-infected juveniles and serum from adults hyperimmunized with the WSHV-2 from the ovarian fluid were used to compare the adult and subadult viruses. The 2 agents were neutralized with these 2 sera which conversely failed to neutralize WSHV-1 at the lowest dilution tested. Our studies demonstrate that at least 2 pathogenic herpesviruses are found among white sturgeon. The newly recognized WSHV-2 can cause both acute and chronic infections and possibly a latent carrier state in white sturgeon. WSHV-2 is the fourth virus to be observed as a cause of juvenile mortality among intensively reared white sturgeon populations.

KEY WORDS: Herpesvirus . Skin lesion . Sturgeon

Published in DAO Vol. 22, No. 3 (1995) on July 13
ISSN: 0177-5103. Copyright © Inter-Research, Oldendorf/Luhe, 1995