The effect of recombinant virus infection on mRNA expression levels in tadpoles was assessed using real time PCR. Treated and control animal groups were sampled at stages 20, 28, 33, 42 and 1-2 weeks post tail resorption (Table 2) . At stage 20, after infection and rinsing, no virus was detected in any animals indicating that there was no background level of BIV detectable by real time PCR and that any virus detected at later stages was the result of virus replication.