Potency Test of Locally Isolated Lentogenic Strain Vaccine with Commercial F1 Vaccine of Ranikhet Disease

The devastating outbreaks of Ranikhet disease from time to time and consequent loses incurred by broiler industry made its way to be included into the list A diseases of OIE long back. A cost-effective preventive measure to avoid this calamity depends on the affordability of the marginal farmers rather than the intensive poultry production units, therefore preparation of cheaper vaccine with sufficient protective efficiency is the need of the hour. It has been proved that commercially available F strain vaccines and modified F vaccines have low margin of safety and cannot effectively protect disease caused by local strains. Need of RD vaccine with locally isolated lentogenic strain arises due to the reason that paramyxoviruses, when spread through a population, undergo mutation and selection resulting in gradual change of structure of hemagglutinin. These structural changes eventually result in a significant alteration in the antigenicity of the virus. In view of these, a locally isolated lentogenic strain of RDV was attenuated by deliberate serial passages in embryonated SPF eggs and was used for the establishment of master seed virus in the form of lyophilized aliquots. A working seed sample of the virus was prepared keeping the structural integrity intact. Few more passages were given to have high hemagglutination titer and the vaccine was prepared in lyophilized form. EID50 for the vaccine was calculated to determine the vaccine dose and comparative efficacy of the prepared vaccine was done with the commercial vaccine by performing sterility, safety and potency tests.