• 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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