Experimental and field evaluation of a live vaccine against avian pneumovirus

The attenuation of an avian pneumovirus (APV) isolate (APV/MN/turkey/1-a/97) by 63 serial passages in cell culture (seven in chicken embryo fibroblasts and 56 in Vero cells) and its evaluation as a live attenuated vaccine in turkey poults is described. The birds were vaccinated with two different doses of attenuated virus (10(4.5) median tissue culture infectious dose (TCID(50))/ml and 10(2.5) TCID(50) /ml) at 2 weeks of age, and were challenged...