The aim of this analysis was to characterise the temporal pattern of infection during the 1997/98 classical swine fever (CSF) epidemic in The Netherlands and hence identify and quantify risk factors for infection in different enterprise types and areas. Survival analysis and Cox proportional hazards regression were used to describe the epidemic. Substantial differences in temporal survival patterns (herd breakdown rate) were found between areas where different control policies operated. Factors with a significant influence on the infection hazard of individual herds included: sow numbers as a percentage of total sows and fatteners (HR = 3.38 for mixed herds (0.1–60% sows) vs. fattening herds (0% sows) and HR = 2.74 for breeding herds (60–100% sows) vs. fattening herds), the number of ‘transport contacts per month’ (>0.3 vs. <0.3; HR = 4.11), pig density (pigs/km2) in the area (HR1000 pigs 1.48) and herd size (HR100 pigs = 1.01).
Pre-emptive slaughter in an area appeared to be associated with lower subsequent disease levels. Higher frequency of transport contacts for welfare slaughter during the epidemic, however, well regulated and controlled, was associated with a substantially higher risk of becoming infected. The positive association of a higher pig density with CSF indicates the potential importance of local spread as a factor in disease transmission and emphasizes that dilution of the pig population can contribute to reduction in CSF occurrence. This analysis suggests however, that if pre-emptive slaughter can promptly be applied effectively in an area after initial diagnosis, pig density is then not a significant factor. Mixed and breeding herds had a higher probability of becoming infected than fattening herds, possibly due to different types and frequencies of inter-herd contacts. These contacts continue to some extent during the epidemic, despite the standstill of animal movements. 相似文献
为了研究三峡大坝修建后库区生态环境的变化,探究大坝修建对库区底泥细菌群落结构和多样性的影响,2013年夏季在香溪河回水区(河口、中游)与河流区(上游)依次选取6个采样点,通过构建16S r DNA基因克隆文库,分析底栖微生物群落结构和多样性的变化规律。结果表明,香溪河调查水域共检出细菌类群15门、87属。在门水平上,回水区和河流区的优势菌门均为变形菌门;在属水平上,回水区和河流区的优势菌属存在显著差异(P0.05),很可能是由于受长江回水和支流高岚河影响所致。芽孢杆菌属所占的比例,从回水区的河口处至中游处逐渐减少至河流区消失,结合芽孢杆菌属易生活在底泥深处的特性,很可能由于大坝的修建,香溪河的上游(即河流区)底泥冲刷至下游(即回水区)河段,被三峡大坝拦截而沉积下来,导致越靠近大坝处,芽孢杆菌属的含量越高。在底泥细菌群落多样性中,Simpson、Shannon和Margalef多样性指数空间分布总体上呈"中间高、两头低"的规律;3种多样性指数最高的采样点均出现在回水区,且回水区的多样性指数均高于河流区,很可能是因其还与旧州河、卜庄河以及周溪河这些支流的交汇,导致河流区底泥细菌群落多样性不稳定。三峡大坝对香溪河底栖微生物的群落结构和多样性产生了显著影响,而大坝修建导致库区回水区水深增加、流速降低、底层水温变化、泥沙沉积增加等因素是造成这种差异的可能原因。 相似文献