Newcastle disease (ND) is the most important viral disease of poultry in the world including developing countries. In Africa and Asia, it is a major constraint against the development of both Industrial and village poultry production. A serological study was conducted to estimate the level of circulating antibodies against ND in unvaccinated local chickens, raised under traditional management system in Nsukka, Enugu State, Nigeria. Newcastle disease virus (NDV) antigen (La sota strain) was obtained and Haemagglutination inhibition (HI) test was used to analyse four hundred (400) chicken sera comprising 252 live bird market chickens, 88 household chickens for NDV antibodies from randomly selected live bird markets and households in four Local Government Areas (LGAs) within Nsukka zone. The LGAs include Udenu, Nsukka, Igbo-Eze South, and Igbo-Eze North LGAs. The remaining 60 chickens used as control were from vaccinated chicken flocks. An overall seroprevalence rate was found to be 60.3% (205/340), and only 47.1% (160/340) of chicken sera had HI antibody titre of ≥ 4log2 which was considered protective. A seroprevalence rate of 65.1% (164/252), 46.6% (41/88), and 86.7% (52/60) were obtained from live bird markets, households, and control groups respectively. About 52.9% (184/340) of chickens sampled were at risk of suffering from clinical ND. A Geometric Mean of HI antibody titre (GMT) of 207.9, 11.3, and 27.9 were obtained from live bird markets, households, and control groups respectively. There was no significant difference (P > 0.05) in antibody prevalence between live bird market and household chickens when compared in each of the four LGA except in Nsukka (P < 0.05). However, there was a significant difference (P < 0.05) in the overall antibody prevalence rate between live bird market chickens and household chickens. There was also a significant difference (P < 0.05) in the overall prevalence rates between the age groups. Higher antibody titre was observed in older chickens (above 24weeks). A seroprevalence rate of 60.3% NDV antibodies in apparently healthy chickens observed in this study is suggestive of the presence and continuous circulation of NDV among them and their role in maintaining endemicity of the virus. Hence, improvement of extension services to rural farmers, biosecurity measures, vaccination programmes and routine vaccination with ND vaccine especially thermostable vaccines such as NDV2 or NDV4 for local chickens as a means of protecting them against ND before the period of outbreak is highly recommended.

Newcastle Disease (ND) is the most important viral disease of poultry in the world including developing countries (Adene, 1999; Spradbrow, 1997). In Africa and Asia ND is a major constraint against the development of both industrial and village poultry production (Alders et al., 2001). ND has been reported as one of the greatest constraints to the development of rural poultry production in Nigeria (Shamaki et al., 1989; Oladele et al., 2003). ND is a highly contagious and commonly fatal ribonucleic acid virus infection of birds which can cause up 100 percent mortality in susceptible chickens. Many avian species may become infected but dramatic losses are seen most often in domestic fowl and to a lesser extent in turkeys and Pheasants (Rosenbeger, 1981; Vickers and Hanson, 1982; Gordon and Jordan,1982)

ND is caused by avian paramyxovirus type-1(APMV-1) which is classified with other paramyxoviruses in the genus Avulavirus, subfamily paramyxovirinae, family paramyxoviridae, and order mononegavirales. It is an enveloped virus and has a negative sense single strand RNA genome.