Evaluation of an ovine testis cell line (OA3.Ts) for propagation of capripoxvirus isolates and development of an immunostaining technique for viral plaque visualization.

An ovine testis cell line (OA3.Ts) was evaluated and compared with primary lamb kidney (LK) cells for its utility in capripoxvirus propagation and titration. A comparison of OA3.Ts cell growth kinetics and morphology at low (<33) and high (34-36) passage levels indicated a difference in both characteristics. However, viral titers determined in low and high passage OA3.Ts cells were comparable with those obtained using LK cells. Capripoxvirus infection of OA3.Ts and LK cells resulted in a similar cytopathic effect, which allowed for the detection of discrete viral plaques following immunostaining with capripoxvirus-specific antiserum.

Serial passage of foot-and-mouth disease virus in sheep reveals declining levels of viraemia over time.

If an infectious agent is to maintain itself within a closed population by means of an unbroken serial chain of infections, it must maintain the level of infectiousness of individuals through time, or termination of the transmission chain is inevitable. One possible cause of diminution in infectiousness along serial chains of transmission may be that individuals are unable to amplify and transmit comparable levels of the infectious agent. Here, the results are reported of a novel experiment designed specifically to assess the effects of serial passage of foot-and-mouth disease virus (FMDV) in experimental groups of sheep. A virus isolate taken from an epidemic of foot-and-mouth disease (FMD) characterized by rapid fade-out of infection was passed serially through four groups of sheep housed in an isolation unit. Although it was not possible to measure individual infectiousness directly, blood virus load from infected individuals was quantified using a real-time PCR assay and used as an underlying indicator of the level of infection. The results of this assay concurred well with those of the traditional tissue-culture assay and were shown to be highly repeatable. The level of peak viraemia was shown to fall significantly with the time of infection and with passage group, both in terms of the group mean and regression analysis of individual values, suggesting that this isolate of FMDV may, under certain conditions, be unable to maintain itself indefinitely in susceptible sheep populations. The results of these experiments are discussed in terms of the epidemiology of FMD in sheep.