Virus excretion and changes in virulence of type 1 paramyxovirus of pigeons following passage through chickens

: Paramyxovirus type 1 of pigeons (strain PMV1-D) was transmitted by sequential contact over nine groups of SPF chicks. The first and last (9th) passages were made in 12-day-old SPF chicks, whereas the others were made in day-old chicks. Mortality was much higher in the last passage group than it was in the first group. None of the day-old chicks survived the PMV1-D infection. Increased virulence of PMV1-D for chickens following passages was also found to be present by the virus characterisation indexes, the EID50, the ICPI and the IVPI in particular.