PCR and RT-PCR analysis of infection and transcriptional activity of walleye dermal sarcoma virus (WDSV) in organs of adult walleyes (Stizostedion vitreum)

The pathogenesis of walleye dermal sarcoma virus (WDSV) infection was investigated in adult walleyes (Stizostedion vitreum). Three tumor-bearing and three tumor-free walleyes were collected in the spring from Oneida Lake, New York, and analyzed for viral infection and transcriptional activity. Specifically, the target organs for viral infection and supporting viral transcriptional activity were determined by assessing for the presence of WDSV DNA and RNA in the brain, liver, kidney, skin, and spleen. For each organ, WDSV DNA and RNA were detected using the polymerase chain reaction (PCR) and reverse transcription PCR (RT-PCR) respectively. Quantitative estimates of the number of viral DNA and RNA copies were obtained in each case by comparing the signal intensity of the sample to that of external controls. WDSV RNA/DNA ratios, based on those quantitative estimates, were computed for each organ. An RNA/DNA ratio of 3 was arbitrarily chosen as the threshold above which there was viral transcriptional activity. Viral DNA was found in all the organs examined from the three tumor-free walleyes. In those three tumor-free walleyes, low levels of WDSV RNA were detected in only one kidney and two spleen samples. In the three tumor-bearing walleyes, viral DNA was found in one brain, one kidney, two liver, and two skin samples. In contrast to the few organs from tumor-free walleyes in which WDSV RNA was detected, in tumor-bearing walleyes WDSV RNA was present in the one brain examined and in 2/3 kidney, 2/3 liver, 3/3 skin, and 3/3 spleen samples. A WDSV RNA/DNA ratio above 3 was obtained in all three tumor-bearing walleyes but in only one tumor-free fish. These data indicated that 1) both tumor-bearing and tumor-free walleyes were infected by WDSV, 2) many cell types were targeted by WDSV and supported viral transcription, and 3) tumor-bearing walleyes harbored a transcriptionally active WDSV, whereas tumor-free walleyes contained mostly silent WDSV DNA.