A one-night downtime period prevents the spread of porcine reproductive and respiratory syndrome virus and Mycoplasma hyopneumoniae by personnel and fomites (boots and coveralls) - Part 1
This paper summarizes observations recorded over a 4-year (1438-day) period regarding the ability of a 1-night period of downtime to prevent mechanical spread of porcine reproductive and respiratory syndrome virus and Mycoplasma hyopneumoniae between pig populations by personnel and fomites.
关键词:猪,猪繁殖和呼吸综合症,隔离,人员,污染物
Keywords: swine, porcine reproductive and respiratory syndrome, downtime, personnel, fomites
The practice of restricting personnel entry to swine farms for extended periods of time following contact with other pigs (downtime) is a highly controversial subject throughout the global swine industry. For many years, downtime periods ranging from 48 to 96 hours have been enforced to reduce the risk of pathogen introduction to farms by personnel, despite a lack of data supporting these periods of time. In the literature, Sellers et al1 investigated the ability of people to harbor foot-and- mouth disease virus following exposure to infected swine. Results indicated the presence of one positive nasal swab from one person 28 hours post exposure, but not at 48 hours post exposure; however, attempts to replicate these results have not been successful.2 Likewise, Amass et al3 reported the recovery of porcine reproductive and respiratory syndrome virus (PRRSV) RNA from fingernail rinses and nasal swabs 5 and 24 hours, respectively, following contact with infected pigs; however, the viability of PRRSV in these samples was not confirmed and transmission to naive sentinels was not observed. Finally, Otake et al4 recovered infectious PRRSV from the hands, boots, and coveralls of personnel following contact with infected animals and demonstrated transmission to naive sentinels. However, this study also demonstrated that basic sanitary interventions such as showering and changing clothing and footwear could pre- vent mechanical spread of PRRSV, irrespective of downtime.4 Collectively, these data challenge the value of extended downtime periods; therefore, to better understand this risk, we summarized observations regarding the ability of a 1-night downtime period to prevent the mechanical spread of PRRSV and Mycoplasma hyopneumoniae (Mhyo) from infected to susceptible populations by personnel and fomites.
材料和方法
Materials and methods
本研究采用明尼苏达大学动物护理和使用委员会批准的方案进行。
This study operated using protocols approved by the University of Minnesota Institute of Animal Care and Use Committee.
Our observations were recorded in conjunction with a 4-year evaluation of area spread and biosecurity of PRRSV and Mhyo conducted at the Swine Disease Eradication Center Production Region Model (St Paul, Minnesota) over the period 2006-2010.5,6 For the purpose of this report, we will focus on activities that occurred in three facilities that were utilized throughout the 4-year area spread and biosecurity project: the source population, the on-site residence, and the high-level biosecurity building (Figure 1).
The source population contained three hundred 25- to 120-kg pigs that had been experimentally inoculated with PRRSV MN-184 during years 1 to 4 and with Mhyo strain 232 during years 2 to 4.5,6 This was a continuous-flow population; therefore, the facility was never emptied during the entire 4-year study. New animals, approximately 6 to 8 weeks in age, entered this facility every 2 to 4 weeks depending on the experimental design of the current study.5,6 New animals were placed in pens adjacent to existing animals, allowing for nose-to-nose contact and circulation of pathogens from infected to naive animals. Throughout the course of the study, clinical signs of respiratory disease and shedding of PRRSV and Mhyo within the population were documented, and a 10% to 12% annual mortality was recorded.5,6
The on-site residence was a house on the Swine Disease Eradication Center premises that served as a shower-in, shower-out facility for personnel and a site for washing farm-specific clothing and disinfection of farm-specific footwear.
Finally, the high-level biosecurity building was a swine facility which contained 10 animals naive for PRRSV and Mhyo throughout the project. This facility was operated using all-in, all-out pig-flow principles; therefore, new batches of animals entered every 2 weeks during year 1 (a total of 26 batches of pigs during year 1) and every 4 weeks during years 2 to 4 (a total of 39 batches of pigs across years 2 to 4). The biosecurity program for this facility consisted of a series of scientifically validated interventions for all direct and indirect routes of PRRSV and Mhyo transmission, including an air filtration system designed to prevent introduction of PRRSV- and Mhyo-contaminated bioaerosols.5-7
Again, for the purpose of this report, we will focus on three specific activity periods that occurred daily throughout the 4-year area spread and biosecurity project: the contamination period, the sanitation and downtime period, and the monitoring period. The contamination period occurred from approximately 2 pm to 4 pm Central Standard Time (CST) each day. The purpose of this period was to expose study personnel to PRRSV- and Mhyo-infected animals. During the contamination period, personnel entered all 11 pens in the source-population facility, where they fed animals, cleaned pen floors, treated sick pigs, removed dead animals, and completed necessary repair work. On an average working day, one or two people would have entered each facility. On a monthly basis, personnel also marketed finished animals and sampled the population to monitor its PRRSV and Mhyo status. Following completion of the contamination period each day, personnel left the facility and initiated the sanitation and downtime period.
The sanitation and downtime period occurred immediately after the contamination period and ran from approximately 4 pm to 6 am CST. The purpose of this period was to neutralize the effects of the contamination period. During this period, personnel moved from the source population to the on-site residence where they removed farm clothing and footwear, took a shower, donned street clothing and footwear, and refrained from pig contact from approximately 4 pm that afternoon until approximately 6 am the next morning. Farm-specific clothing was washed and footwear was disinfected using 7% glutaraldehyde and 26% quaternary ammonium chloride (Synergize; Preserve International, Atlanta, Georgia). At approximately 5:30 am CST on the following day, personnel took another shower, donned clean farm-specific clothing and footwear, and entered the high-level biosecurity building for initiation of the monitoring period.
The monitoring period was the third and final period pertaining to this report and occurred in the high-biosecurity building from approximately 6 am to 8 am CST each day. The purpose of this period was to measure the efficacy of the practices utilized during the sanitation and downtime period. Specifically, two outcomes were measured: detection of PRRSV and Mhyo on personnel and the PRRSV-Mhyo status of sentinel animals housed in the facility. Upon completion of the sanitation and downtime period, personnel moved immediately from the on-site residence to the high-level biosecurity building, a distance of approximately 100 m. Upon entry into the facility-specific anteroom, a swabbing protocol, designed to determine if PRRSV RNA or Mhyo DNA was present on personnel, clothing, and footwear, was conducted.5,6 For collection of samples, Dacron swabs (Fisher Scientific, Hanover Park, Illinois) were immersed in minimal essential medium (MEM) supplemented with 3% fetal calf serum (Difco, Detroit, Michigan) and swiped using a zigzag pattern across each person’s head, face, neck, torso, hands, arms, and legs. Swabs were then stored in MEM at -20°C to maintain viral integrity and maximize testing sensitivity until laboratory analysis could be conducted 24 to 48 hours post collection. Following sampling, facility-specific boots, coveralls, and gloves were donned and boots were disinfected using 7% glutaraldehyde and 26% quaternary ammonium chloride. Personnel then entered the animal air space, fed pigs, and cleaned pens. In addition, on a weekly basis, a diagnostic assessment of the health of this 10-pig population was conducted, involving visual observation of clinical signs of respiratory disease and blood testing and nasal swabbing of all 10 pigs. Immediately following collection, all samples from personnel, fomites, and animals were tested for PRRSV RNA and Mhyo DNA by polymerase chain reaction (PCR) at the University of Minnesota Veterinary Diagnostic Laboratory (MN VDL, St Paul, Minnesota).8,9