§ Mr. Priorasked the Minister of Agriculture, Fisheries and Food whether he is aware that some flocks infected with fowl pest and previously treated with the vaccine show worse symptoms of paralysis than non-vaccinated birds; and if he will give details of the information he has received on this matter.
§ Mr. Scott-HopkinsI am aware of one large flock reared under intensive conditions and said to have been fully vaccinated in which fowl pest was confirmed and paralysis was more acute and more widespread than is normal in an unvaccinated flock. This is the only case of its kind on record and in general disease symptoms in vaccinated flocks are markedly less severe than those in unvaccinated flocks.
The laboratory investigation of the virus which was recovered from this flock showed that its behaviour under test was within the range of other known field strains of virus responsible for sub-acute fowl pest. Detailed investigations were made for other diseases which might have contributed to the high incidence of paralysis, but all laboratory tests for these were negative. A number of other outbreaks of fowl pest confirmed in vaccinated and unvaccinated flocks in the same district as the outbreak in question were attributed to spread from it, and in all of these the disease ran a typical course, with no evidence of an unusual amount of paralysis.