Retroviral properties inherent to viral erythrocytic infection in sea bass.

The characterization of the aetiological agent of viral erythrocytic infection (VEI) of sea bass suggests a retroviral origin of the disease. RNA from viral erythrocytic infection virus (VEIV) and DNA from blood and organs of VEI-affected fish hybridized to a specific retrovirus cDNA probe. Sequences homologous to retrovirus genome were also detected in non-infected SBL cells (a sea bass cell line), however, Southern blot analysis showed that the DNA restriction patterns in VEI-affected erythrocytes differed from those of SBL cells. RNA-dependent DNA polymerase activity was detected in VEI-affected sea bass blood. This reverse transcription was strongly Mn(2+)-dependent and is the first report of its occurrence in a marine fish and in fish blood samples. Nucleic acid sequences homologous to retrovirus RNA were detected in chromatographic fractions exhibiting reverse transcriptase activity and the presence of virus-like particles, 125-150 mm in diameter. The density of VEIV in sucrose was 1.17-1.18 g/cm3. The symptomatology of VEI is not far from those described for some retroviral diseases.