Prevalence and incidence of Newcastle disease and prevalence of Avian Influenza infection of scavenging village chickens in Timor-Lesté

Abstract

A longitudinal study to monitor prevalence and incidence of antibodies against Newcastle disease (ND) virus and prevalence of antibodies against Avian Influenza (AI) virus in scavenging village chickens was conducted in 20 villages within 4 districts of Timor-Lesté. A total of 3600 blood samples was collected from 1674 individual birds in 300 household chicken flocks during three sampling periods (December 2008–February 2009, March–May 2009, and June–August 2009). The mean interval between household visits was 101.6±1.9 days. None of the birds enrolled in the study was vaccinated against ND or AI. A haemagglutination inhibition (HI) test was used to determine antibody titres against ND virus and a competitive ELISA and HI tests were used to detect antibody against AI virus.The bird-level ND seroprevalence pooled across all samplings (adjusted for clustering by households) was 4.4% (95% CI 3.5–5.2). The bird-level ND seroprevalence in each of the three sampling periods (adjusted for clustering by household) was 3.0% (95% CI 2.0–4.0), 6.6% (95% CI 5.1–8.0) and 3.6 (95% CI 2.5–4.6), respectively. A total of 12.6% individual birds tested ND seropositive at least once over the total study period (95% CI 10.5–14.7).The flock-level ND seroprevalence (at least one bird tested had antibodies against ND virus) pooled across all samplings was 15.9% (95% CI 13.5–18.3). A total of 35.3% flocks had a minimum of one bird being ND seropositive at least once over the study period.The bird-level incidence rate for the period between the first and the second sampling and between the second and the third sampling was 5.6 (95% CI 4.1–7.5) and 0.5 (95% CI 0.5–3.8) per 10,000 bird-years-at-risk, respectively.A total of 1134 serum samples from the last sampling period between June and August 2009 was tested for antibodies against AI virus. Only 4 samples tested Influenza A positive, indicating a bird-level seroprevalence level for Influenza A of 0.4% (CI 0.0–0.7%). These Influenza A positive samples were further tested for HI antibodies against AI virus subtypes of H5N1, H5N3, H7N3 and H9N2, but all tested negative, suggesting that the influenza antibodies in those four birds resulted from exposure to low pathogenic AI viruses of different H subtypes.Our results indicate that village chickens in Timor-Lesté are exposed to ND virus; there was a higher risk of infection during the early months of 2009 than either immediately prior or subsequent to this. No evidence of infection of village chickens with H5, H7 or H9 AI viruses was detected in this study.