Control of Newcastle disease and duck plague in village poultry

A serological survey on the prevalence of antibodies to Newcastle disease virus was carried out in 2 communes of Phu Vang District, Thua Thien Hue Province, Central Vietnam. Villagers in the district keep chickens under either scavenging or enclosed backyard systems. Villages in each commune and households in each village were selected randomly. Approximately 30% of household flocks in each village were sampled, 10% with scavenging chickens and 20% with backyard chickens. One or 2 birds from each scavenging flock and 1–6 birds from each backyard flock were sampled. Approximate ages of the chickens and vaccine status of the flocks were recorded. Blood samples were collected from 400 chickens in the dry season and 400 again in the rainy season, and sera were tested for haemagglutination inhibition (HI) antibodies against Newcastle disease virus. Comparisons were made between ages and breed of chickens, system of husbandry, season and vaccination status. A La Sota-based vaccine was used in some flocks. Overall, a significantly higher proportion of vaccinated birds had protective antibody titres (≥3 log2) compared to unvaccinated birds and the mean titre was significantly higher in vaccinated birds. There was no significant difference between seasons in the percentage of birds with protective titres. The percentage of vaccinated and unvaccinated birds with protective titres was significantly higher in the ≥6-month age group compared to the <6-month age group. Within unvaccinated birds, a significantly higher proportion of scavenging birds and birds of local breed had protective titres compared to backyard birds and exotic breeds, respectively. Within vaccinated birds, the prevalence of protective titres was significantly higher in Phu Thuong Commune compared to the Phu Mau Commune. The possible reasons for these differences are discussed.