Comparative Studies on the Large & Small Plaque Producing Strains of Bovine Para-Influenza- 3 Virus

A strain of para-influenza-3 virus locally isolated and successfully propagated in primary calf kidney tissueculture cells was used in this investigation. Using the plaque technique and the terminal dilution method, two variants could be detected in the original virus population. They did not differ in most of theirphysical and chemical properties (thermal inactdiethyl ether and chloroform, cytopathogenis changes,andhaemagglutination properties), and the only difference wasin the morphology and size of the produced plaques. By serial passage of a single plaque population the smallerplaque increased gradually in size attaining the larger plaque size by the 8th passage, yet the aformentioned pro-perties were not stable to identify strains or variants within the same original population or to be considered as markers Intra-nasal intallation of bov.tno s with PI-3 virus was followed by an increase in both the serum specific antibodies and the nasal