A polyoma-like virus associated with an acute disease of fledgling budgerigars (Melopsittacus undulatus).

A virus previously isolated from fledgling budgerigars (Melopsittacus undulatus) suffering from an acute disease, has been purified and the structural characteristics have been determined. The virions with a buoyant density of 1.34 g/ml are non-enveloped icosahedral particles with a diameter of about 46-48 nm. Their DNA genome has a molecular weight of about 3.3 X 10(6) d, and exists as supericoiled circular, relaxed circular, and linear molecules. There are eight structural proteins, the most abundant of which has a molecular weight of about 42,000 d. Empty capsid shells with buoyant densities of 1.31 g/ml are similar in size and shape, but lack DNA and histone-like polypeptides. Virus replication in chicken embryo cells results in cytopathic changes characterized by rounding and enlargement of the nucleus, and formation of intranuclear inclusion bodies. All these properties justify classification of the virus as polyoma-like.