Evidence for the isolation of a virus from this epizootic disease of shearwaters is based upon the reproduction of a similar condition in ducklings and pigeons and upon the development of characteristic histological changes with cytoplasmic eosinophilic inclusions in inoculated chorio-allantoic membranes of chick embryos.It was not possible to reproduce the original disease exactly by inoculation of shearwaters with egg-passage virus from the previous season because the birds did not develop blisters at the site of inoculation of the web. Nevertheless, three out of four birds died and the agent was re-isolated from the spleen of one of them.The ability of the virus to cause blisters on duckling webs was neutralized by shearwater serum taken at the convalescent but not at the acute stage of the disease, and complement fixation was obtained with convalescent shearwater serum.

Previous studies on natural virus infections of birds have been mainly limited to psittacosis and ornithosis, the pox viruses, Newcastle disease virus and some of the neurotropic viruses. However, the failure to infect mice by any route, and the ability of the shearwater virus to pass through filters with an A.P.D. of 48 mμ, seemed to rule out the psittacosis group as a cause of the infection. The ability of the virus to cause vesicles and the intracytoplasmic eosinophilic inclusion bodies suggested a member of the pox group of viruses, but the small size of the agent renders a relation to either the pox group or Newcastle disease virus unlikely. Several of the neurotropic viruses which infect birds, for example, Japanese B virus, are about the size of the shearwater virus, but they do not cause the formation of inclusion bodies and they are all pathogenic for mice. Foot and mouth disease virus is also of small size and produces vesicular lesions, but it is unlikely that the shearwater virus is the same since it was unable to infect a cow or the pad of a guinea-pig, and it grew in eggs more readily than foot and mouth disease virus.

There has obviously been insufficient work on the agent to postulate a new virus, but the properties described do not justify its classification in any of the known virus groups. The name puffinosis which was originally suggested still seems suitable for this disease of Puffinus puffinus puffinus.