Department of Mathematics, Faculty of Science, Gulu University, Gulu, Uganda.
International Livestock Research Institute, Ibadan, Nigeria.
Transbound Emerg Dis. 2018 Feb;65(1):e127-e134. doi: 10.1111/tbed.12692. Epub 2017 Aug 14.
Highly Pathogenic Avian Influenza (HPAI) is classified by the World Organization for Animal Health as one of the notifiable diseases. Its occurrence is associated with severe socio-economic impacts and is also zoonotic. Bangladesh HPAI epidemic data for the period between 2007 and 2013 were obtained and split into epidemic waves based on the time lag between outbreaks. By assuming the number of newly infected farms to be binomially distributed, we fit a Generalized Linear Model to the data to estimate between-farm transmission rates (β). These parameters are then used together with the calculated infectious periods to estimate the respective basic reproduction numbers (R ). The change in β and R with time during the course of each epidemic wave was explored. Finally, sensitivity analyses of the effects of reducing the delay in detecting infection on a farm as well as extended infectiousness of a farm beyond the day of culling were assessed. The point estimates obtained for β ranged from 0.08 (95% CI: 0.06-0.10) to 0.11 (95% CI: 0.08-0.20) per infectious farm per day while R ranged from 0.85 (95% CI: 0.77-1.02) to 0.96 (95% CI: 0.72-1.20). Sensitivity analyses reveal that the estimates are quite robust to changes in the assumptions about the day in reporting infection and extended infectiousness. In the analysis allowing for time-varying transmission parameters, the rising and declining phases observed in the epidemic data were synchronized with the moments when R was greater and less than one, respectively. From an epidemiological perspective, the consistency of these estimates and their magnitude (R ≈ 1) indicate that the effectiveness of the deployed control measures was largely invariant between epidemic waves and the trend of the time-varying R supports the hypothesis of sustained farm-to-farm transmission that is possibly initiated by a few unique introductions.
高致病性禽流感（HPAI）被世界动物卫生组织列为应报告的疾病之一。它的发生与严重的社会经济影响有关，并且具有动物源性。获得了 2007 年至 2013 年期间孟加拉国 HPAI 流行数据，并根据疫情之间的时间间隔将其分为流行波。通过假设新感染农场的数量呈二项式分布，我们使用广义线性模型对数据进行拟合，以估计农场之间的传播率（β）。然后，使用这些参数以及计算出的感染期来估计各自的基本繁殖数（R）。在每个流行波的过程中，研究了β和 R 随时间的变化。最后，评估了减少发现感染的农场时滞以及延长感染农场的感染期对感染农场时滞的影响。获得的β点估计值范围为 0.08（95％置信区间：0.06-0.10）至 0.11（95％置信区间：0.08-0.20），每个感染农场每天有 0.08 个，R 的范围为 0.85（95％置信区间：0.77-1.02）至 0.96（95％置信区间：0.72-1.20）。敏感性分析表明，这些估计值对感染报告和延长感染期的假设变化非常稳健。在允许时变传播参数的分析中，观察到的流行数据中的上升和下降阶段与 R 大于和小于 1 的时刻分别同步。从流行病学角度来看，这些估计值的一致性及其大小（R≈1）表明，所部署的控制措施的有效性在流行波之间基本不变，时变 R 的趋势支持了持续的农场间传播的假设，这可能是由少数独特的引入引发的。
