S-61. Marker vaccine against newcastle disease affecting poultry

India is one of the largest producers of eggs in the world and the growth rate in poultry industry is a whooping 5.87% per annum. Despite the advancements, poultry industry in India is incurring losses. The most important reson for such losses is the infectious diseases, the incidences of which are complicated by the emergence of new virulent strains, transboundry infections and reemergence of hitherto controlled infections. Most of these infections besides causingheavy mortality, also lead to a substantial production loss in the poultry industry. Newcastle disease (ND) is one such important disease. It is caused by the Newcastle disease virus (NDV) (Alexander, 1997), which is an economically important avain virus that causes severe loss to the poultry industry and it causes up to 60% mortality among chickens in many developing countries. In most of the countries, the control strategy against ND is aimed at regular vaccination of flocks followed by periodic sero-monitoring by haemagglutination inhibition (HI) test or by enzyme linked immunosorbant assay (ELISA). Though this system is effective to a certain extent, an eradication programme could not e developed due to failure of this system particularly to differentiate between vaccinated and infected chickens. As a consequence to this, birds suffering from mild infection go undetected and they act as reservoirs leading to servere m mortality and production loss. Hence, it becomes imperative to have a vaccine, which will help in differentiation of infected birds from vaccinated birds. There are a number of vaccines available like the live attenuated and inactivated vaccines to control ND using different NDV strains/isolates from respective areas. None of these vaccines help in differentiation of infected from vaccinated and as a result the world is yet experiencing outbreaks of ND and it still remains a great threat. this further emphasizes the need to develop an alternative streategy to control and eradicate ND by using mnarker vaccines. Marker vaccines are unique vaccines that either lack a characteristic peptide or posses a novel peptide that is not present in the wild type strains of virus and in conjunction with a diagnostic test, referred as companion discriminatory test, enables serological differentiation of vaccinated brirds from infectd birds. In the present paper, work so far carried out with regard to the development of marker vaccine to control Newcastle disease and the proposed strategy will be discussed, which include indentification of virus strain(s), their molecular characterization, rationale behind selection of gene for modification, sequence analysis, prediction of epitopes, confirmation of the immunodominance of the epitope selected, expression of the gene, synthesis of epitope etc. will be discussed in detail. Of the six major genes of NDV namely NP, P, M, HN, F and L, NP has been selected. The sequence of NP gene of four common vaccine strains used in India has been analysed and twenty different epitopes have been predicted. One epitope, which has been found to be conserved among vaccine strains, has been synthesized and its immunodominance was confirmed by enzyme immunoassay. Antibody response in birds to whole virus protein, recombinant NP and epitope has been studied by ELISA. The results of these and future strategies will be presented.