School of Veterinary Science, University of Queensland, Gatton 4343, Queensland, Australia.
Prev Vet Med. 2012 May 1;104(3-4):301-8. doi: 10.1016/j.prevetmed.2011.12.018. Epub 2012 Jan 23.
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.
本研究在东帝汶四个地区的 20 个村庄中，对 300 个家庭鸡群中的 1674 只个体鸡进行了 3600 份血液样本的采集，以监测对新城疫（ND）病毒和禽流感（AI）病毒的抗体的流行率和发生率。300 个家庭鸡群中的 1674 只个体鸡被分为 3 组，分别在 3 个时间段（2008 年 12 月至 2009 年 2 月、2009 年 3 月至 5 月和 2009 年 6 月至 8 月）进行采血。家庭访视的平均间隔时间为 101.6±1.9 天。所有参加研究的鸡均未接种 ND 或 AI 疫苗。血凝抑制（HI）试验用于检测对 ND 病毒的抗体滴度，竞争 ELISA 和 HI 试验用于检测对 AI 病毒的抗体。对所有采样进行调整后的 ND 血清阳性率（通过家庭聚类进行调整）为 4.4%（95%CI 3.5-5.2）。三个采样周期中的 ND 血清阳性率（通过家庭聚类进行调整）分别为 3.0%（95%CI 2.0-4.0）、6.6%（95%CI 5.1-8.0）和 3.6%（95%CI 2.5-4.6）。在整个研究期间，共有 12.6%的个体鸡至少有一次 ND 血清阳性（95%CI 10.5-14.7）。所有采样的 ND 血清阳性率（至少有一只鸡对 ND 病毒有抗体）为 15.9%（95%CI 13.5-18.3）。在整个研究期间，共有 35.3%的鸡群至少有一只鸡至少有一次 ND 血清阳性。第一和第二次采样之间以及第二次和第三次采样之间的 ND 发病率分别为 5.6（95%CI 4.1-7.5）和 0.5（95%CI 0.5-3.8）/10,000 鸟年风险。对 2009 年 6 月至 8 月期间最后一次采样的 1134 份血清样本进行了针对 AI 病毒的抗体检测。仅 4 份样本对 Influenza A 呈阳性，表明 Influenza A 的鸡群血清阳性率为 0.4%（CI 0.0-0.7%）。对这 4 份样本进一步进行了针对 H5N1、H5N3、H7N3 和 H9N2 的 AI 病毒亚型的 HI 抗体检测，但均为阴性，这表明这四只鸡的流感抗体是由接触不同 H 亚型的低致病性 AI 病毒引起的。我们的研究结果表明，东帝汶农村地区的鸡群接触到了 ND 病毒；2009 年早期的感染风险高于此前或此后的时期。本研究未检测到农村鸡群感染 H5、H7 或 H9 AI 病毒的证据。
