Norman H S, Sischo W M, Pitcher P, Nesselrodt A, Day R L
Department of Veterinary Science, Pennsylvania State University, University Park 16802, USA.
Am J Vet Res. 1996 Nov;57(11):1563-8.
To examine the pattern of pseudorabies virus (PRV) infection in Pennsylvania and identify the area factors associated with herd quarantine status.
123 PRV-quarantined commercial swine herds identified between 1986 and 1993 were selected as cases, and 162 uninfected herds were selected as controls.
Herd location, demographics, and temporal vaccination and quarantine data for a case-control study were obtained from producer questionnaires and state records, using a database of swine herds from 2 Pennsylvania counties. Any herd that was on quarantine as of Jan 1, 1991, or quarantined subsequent to this date, was defined as a case. A herd was defined as a control if it had never been quarantined for PRV. Controls were group matched to cases by year. Study herds were centered in a circle, or buffer zone, with a 1.61-km (1-mile), 3.22-km (2-mile), or 6.44-km (4-mile) radius, and densities of operation types, quarantined herds, nonquarantined herds, and vaccinated herds in the buffer zone were compared. The analytical outcome was the probability of a herd being quarantined, conditional on the buffer zone density of herds quarantined, herds not quarantined, and herds in which a PRV vaccine was used. These density variables were categorized into high, medium, and low, or just high and low categories. Confounding by year was assessed in the analysis. Analysis was performed, using unconditional logistic regression.
Decreased density of PRV-quarantined herds in the study region was associated with reduced risk of a herd becoming quarantined, whereas increased density of nonquarantined, presumably uninfected herds was associated with decreased probability of a herd becoming quarantined. Decreased density of vaccinated herds was associated with increased probability of a herd becoming quarantined. In addition, being a farrow-to-finish study herd was associated with increased probability of becoming quarantined, compared with being a feeder pig producer study herd.
Associations with quarantine status and area densities of vaccinated, nonquarantined, and quarantined herds indicate the importance of area spread in PRV control. These effects are seen most strongly at a 3.22-km (2-mile) radius, but also are seen at a 6.44-km (4-mile) radius.
研究宾夕法尼亚州伪狂犬病病毒（PRV）的感染模式，并确定与畜群检疫状态相关的区域因素。
选取1986年至1993年间确定的123个被PRV检疫的商业猪群作为病例，162个未感染猪群作为对照。
通过生产者问卷和州记录，利用宾夕法尼亚州两个县的猪群数据库，获取病例对照研究的畜群位置、人口统计学信息以及时间性疫苗接种和检疫数据。截至1991年1月1日处于检疫状态或在此日期之后被检疫的任何畜群被定义为病例。如果一个畜群从未因PRV被检疫，则定义为对照。对照按年份与病例进行组匹配。研究畜群集中在半径为1.61公里（1英里）、3.22公里（2英里）或6.44公里（4英里）的圆形或缓冲区中，并比较缓冲区中经营类型、被检疫畜群、未被检疫畜群和接种疫苗畜群的密度。分析结果是畜群被检疫的概率，条件是缓冲区中被检疫畜群、未被检疫畜群和使用PRV疫苗的畜群的密度。这些密度变量被分为高、中、低或仅高和低类别。在分析中评估年份的混杂因素。使用无条件逻辑回归进行分析。
研究区域内被PRV检疫的畜群密度降低与畜群被检疫的风险降低相关，而未被检疫（推测未感染）畜群密度增加与畜群被检疫的概率降低相关。接种疫苗畜群密度降低与畜群被检疫的概率增加相关。此外，与作为育肥猪生产者研究畜群相比，作为自繁自养研究畜群被检疫的概率增加。
与检疫状态以及接种疫苗、未被检疫和被检疫畜群的区域密度之间的关联表明区域传播在PRV控制中的重要性。这些影响在半径为3.22公里（2英里）时最为明显，但在半径为6.44公里（4英里）时也可见。
