2 Breeding, Transportation, and Use of Pathogen-free Rodents

Past experience has taught that the use of pathogen-free rodents in research is possible only when breeding, transportation, and maintenance programs specifically designed for the exclusion of pathogens are followed. Genuine commitments must be made to preventing infections throughout the life of the rodent. Some of the essential commitments are as follow:*

  1. The investigator must be strongly committed.
  2. The investigator and the support personnel must understand the terminology and principles involved.
  3. Appropriate facilities and equipment must be available.
  4. Housing practices must ensure physical separation and avoidance of cross-contamination between different animal subpopulations throughout their lives.
  5. Reliable health monitoring must be maintained to identify breeding populations free of pathogens and to redefine the microbiological status of the animals at regular intervals after receipt in the user facility until completion of each study.
  6. Written standard operating practices must be developed and followed

*  

From a consensus developed during a seminar entitled "Barrier Maintenance of Rodents in Multipurpose Facilities," held at the Thirty-Sixth Annual Session of the American Association of Laboratory Animal Science on November 3-8, 1985 in Baltimore, Md. Seminar participants were J.R. Lindsey (leader); G.L. Van Hoosier, Jr.; D.B. Casebolt; J.G. Fox; R.O. Jacoby, and T.E. Hamm, Jr.



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--> 2 Breeding, Transportation, and Use of Pathogen-free Rodents Past experience has taught that the use of pathogen-free rodents in research is possible only when breeding, transportation, and maintenance programs specifically designed for the exclusion of pathogens are followed. Genuine commitments must be made to preventing infections throughout the life of the rodent. Some of the essential commitments are as follow:* The investigator must be strongly committed. The investigator and the support personnel must understand the terminology and principles involved. Appropriate facilities and equipment must be available. Housing practices must ensure physical separation and avoidance of cross-contamination between different animal subpopulations throughout their lives. Reliable health monitoring must be maintained to identify breeding populations free of pathogens and to redefine the microbiological status of the animals at regular intervals after receipt in the user facility until completion of each study. Written standard operating practices must be developed and followed *   From a consensus developed during a seminar entitled "Barrier Maintenance of Rodents in Multipurpose Facilities," held at the Thirty-Sixth Annual Session of the American Association of Laboratory Animal Science on November 3-8, 1985 in Baltimore, Md. Seminar participants were J.R. Lindsey (leader); G.L. Van Hoosier, Jr.; D.B. Casebolt; J.G. Fox; R.O. Jacoby, and T.E. Hamm, Jr.

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--> without interruption; clear objectives must be defined in advance along with detailed procedures for reaching those objectives. A range of optional approaches should be considered in the design of specific programs of pathogen exclusion for each investigator or institution. Inasmuch as 65% of the mice and 80% of the rats used for research purposes in the United States are produced by commercial breeding facilities (ILAR, 1980), such programs usually consist of breeding facility, transportation, and user facility components. However, some investigators choose to breed their own animals, eliminating or reducing the transportation component. The following are the range of options within which most investigator or institutional needs can be met (Lindsey et al., 1986a): Option 1:         Animals are unmonitored and obtained from many breeding facilities   Transported in open cartons   Housed in a conventional multi- purpose breeding facility Option 1 is the least effective. Rodents are purchased, transported, and used with little or no regard for pathogen status. They usually harbor many subclinical infections but appear normal. Although such animals may be acceptable for selected research projects, they serve as an important source of contamination for other rodent stocks and, therefore, pose a risk for other research programs in the user facility. Thus, for a variety of reasons this option cannot be recommended. Option 2:         Animals are unmonitored and obtained from barrier breeding facilities   Transported in filter- protected cartons   Housed in a barrier room in a multi- purpose research facility In Option 2 the animals are obtained from a so-called barrier breeding facility, but no health monitoring is done to determine pathogen status. The term barrier is meaningless unless it is supported by current health surveillance data. Such barrier breeding facilities often have rooms containing pathogen-free animals and others that are contaminated with pathogens. Also, they may use a common shipping room where cross-contamination between groups can occur prior to shipping. Thus, the animals may have active infections due to some agents and be incubating other infections upon arrival at the user facility. Filter-protected cartons provide containment transport, but their purpose is largely negated by the infections accumulated prior to shipping. Since the research facility is multipurpose (i.e., houses animals

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--> of different pathogen status, from different sources, and for different research purposes), there are risks of cross-contamination between animal subpopulations, despite the fact that they are housed in a room operated by a barrier program. In essence, this option represents a partial commitment to prevention of pathogen infections, and it is only partially effective. Option 3:         Animals are user and vendor monitored and are from a vendor protected barrier breeding facility   Transported in filter- protected cartons   Quarantined in remote facility until tested and shown free of pathogens; then moved to a barrier facility or barrier room Option 3 incorporates the principles necessary for a high degree of success in preventing pathogen infections. The breeding facility is operated by strict barrier protocol. All subpopulations are pathogen free and are monitored regularly by the vendor for pathogens. The vendor has made a commitment to protecting all subpopulations by promptly eliminating any subpopulation found to be infected by a pathogen (vendor protected facility). The user also regularly monitors subpopulations of the breeding facility to confirm pathogen-free status. All animals are shipped in filter-protected cartons. The user initially quarantines the animals for 4-6 weeks in a separate barrier room at a quarantine facility remote from the research facility (Hoag, 1964; Parker and Richter, 1982). The stock is monitored and found to be free of pathogens and then transferred in filter-protected cartons to a barrier room in the research facility where the experimentation is accomplished. Option 4:         Animals are user maintained, controlled, and monitored and are from protected barrier breeding facility Trexler isolators   Transported in filter-protected cartons   Housed in barrier facility, barrier room, barrier room with filter cages and laminar flow change station, or Option 4 offers maximum effectiveness in preventing pathogen contamination. The user of the animals (or an entire institution) has complete control of the barrier breeding program, containment transfer, housing in the user facility, health surveillance program, and decision making for corrective action if needed. Breeding stocks are preferably gnotobiotic or defined flora animals and are held in isolators in a remote quarantine facility and monitored repeatedly before they are entered into the barrier breeding facility. Animals in both the barrier breeding facility and those involved in experiments are monitored regularly for pathogens. Any breeding

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--> subpopulation in the barrier breeding facility found to have any of the predetermined list of pathogens is immediately eliminated, and health monitoring of other nearby subpopulations is intensified to prevent the spread of infection. Options 1 through 4 are not intended to be separate and distinct systems for preventing pathogen infections. Instead, they are presented here to illustrate general approaches of increasing effectiveness by which individual investigators or institutions can develop those programs most appropriate for their particular needs and resources (Lindsey et al., 1986a).