CHARACTERISTICS AND PATHOGENICITY OF A NOVEL HERPESVIRUS ISOLATED FROM ADULT AND SUBADULT WHITE STURGEON ACIPENSER-TRANSMONTANUS

A syncytium-inducing viral agent was initially isolated from the ovari an fluid of a domestic white sturgeon Acipenser transmontanus female u sing the sturgeon spleen cell line WSS-2. Examination of infected cell s by transmission electron microscopy revealed ultrastructural charact eristics typical of the Herpesviridae. On the basis of differences sho wn by comparative in vitro 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, W SHV (WSHV-1). A water-borne transmission trial at 3 virus concentratio ns was conducted to determine the susceptibility of juvenile sturgeon to the newly isolated virus. At virus doses of 10(5) and 10(4) TCID50 ml(-1) cumulative mortality reached 80% within 6 wk at a water tempera ture of 17 degrees C. Virus was reisolated from all mortalities with c oncentrations approaching 10(7) TCID50 g(-1) in cutaneous epithelial t issues where severe hyperplastic lesions were observed. Challenge with 10(3) TCID50 ml(-1) of WSHV-2 failed to induce clinical signs or mort ality, although chronic subclinical infections were detected in a majo rity of survivors 70 d postchallenge. During our investigations of WSH V-2 from adult sturgeon, a second virus isolation was obtained from ul cerative skin lesions of naturally infected subadult white sturgeon. T his virus induced identical cytopathic effects in WSS-2 cells to that caused by the adult isolate from ovarian fluid. Serum anti-WSHV-2 neut ralizing activity was detected in subadults with skin lesions and amon g fish recovering from these lesions. Serum from naturally-infected ju veniles 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 t o neutralize WSHV-1 at the lowest dilution tested. Our studies demonst rate that at least 2 pathogenic herpesviruses are found among white st urgeon. The newly recognized WSHV-2 can cause both acute and chronic i nfections 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.