Abstract
The growth characteristics of two lines of maedi virus were studied by measurements of released viral RNA, by reverse transcriptase assay and by infectivity assay. The measurements were made from sheep choroid plexus cell culture media collected at different time intervals during an incubation period of 2 weeks. The amount of virus was determined by measuring labelled RNA in culture fluids at 2-day intervals. The extracted virus-specific RNA formed uniform 60–70 S peaks in rate zonal sedimentation gradients. No definite signs of 30–35 S subunits were seen. A prominent increase in 60–70 S RNA production was seen between days 4 and 6 post-infection, after which the amount of viral RNA declined perceptibly. Some differences were observed between the growth curves of the maedi virus lines studied. These results were supported by reverse transcriptase assays. The highest reverse transcriptase activity was between days 4 and 6; for maedi 1320 it was a little earlier than for maedi M88. The activity was still quite high on the 11th day after infection. Virus release was also studied by serial titrations of infectivity. The titre increased conspicuously after 2 days of incubation and levelled off at about 4 days for maedi 1320 but reached a peak at about 6 days after infection for maedi M88.
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