Department of Population Medicine and Diagnostic Sciences, Cornell University, Ithaca, New York 14853, USA.
Foodborne Pathog Dis. 2010 Apr;7(4):467-74. doi: 10.1089/fpd.2009.0411.
Cattle are recognized as an important source of foodborne Salmonella causing human illness, particularly for antimicrobial-resistant strains. The transmission dynamics of multidrug-resistant (MDR) Salmonella after the onset of a clinical outbreak in a dairy farm has been rarely monitored. The early transmission of a pathogen influences the outbreak size and persistence of the pathogen at the farm level and, therefore, how long the herd represents a risk for Salmonella zoonotic transmission. The objective of this study was to describe the transmission dynamics of MDR Salmonella Typhimurium after the onset of a clinical outbreak in a dairy herd. For that purpose, fecal shedding and serological response to MDR Salmonella were monitored in a longitudinal study conducted in a dairy herd after a few cases of salmonellosis, and a stochastic transmission model was developed to predict Salmonella persistence at the pen level. The outbreak was limited to five clinical cases, and only 18 animals out of 500 cows shed Salmonella in feces. The longest shedder was culture-positive for Salmonella for at least 68 days. The isolates (n = 27) were represented by four pulsed-field gel electrophoresis patterns; three patterns were similar. With one exception, isolates were resistant to nine or more antimicrobial drugs. Simulations of the transmission model indicated that approximately 50% of the outbreaks were likely to die out within 20 days after the first animal was infected. The simulation studies indicated that salmonellosis outbreaks with few clinical cases were likely due to the extinction of the pathogen in the premises in the early phase of the outbreaks. Small population size and group structure within the farm decrease the on-farm persistence of the pathogen.
牛被认为是食源性沙门氏菌的重要传染源，可导致人类患病，尤其是对抗菌药物耐药的菌株。在奶牛场发生临床暴发后，很少有研究监测多药耐药（MDR）沙门氏菌的传播动态。病原体的早期传播会影响暴发规模和农场水平上病原体的持续存在，因此，牛群对沙门氏菌动物源传播构成风险的时间长短也会受到影响。本研究的目的是描述在奶牛场发生临床暴发后 MDR 沙门氏菌 Typhimurium 的传播动态。为此，在发生几例沙门氏菌病后，对奶牛场进行了纵向研究，监测 MDR 沙门氏菌的粪便排出和血清学反应，并开发了一个随机传播模型来预测栏舍水平的沙门氏菌持续存在。暴发仅限于五例临床病例，在 500 头奶牛中，仅有 18 头牛粪便中排出沙门氏菌。最长的排菌者至少有 68 天对沙门氏菌呈阳性。分离株（n=27）由四个脉冲场凝胶电泳模式代表；其中三种模式相似。除一例外，分离株对 9 种或更多抗菌药物均具有耐药性。传播模型的模拟表明，大约 50%的暴发很可能在第一头动物感染后的 20 天内消失。模拟研究表明，临床病例较少的沙门氏菌病暴发很可能是由于病原体在暴发早期在养殖场内灭绝。农场内的种群规模小和群体结构会降低病原体在农场内的持续存在。
