Containment Animal Housing

"Containment" refers to animal housing systems designed and managed to prevent the escape of experimental hazardous agents to which the animals have been exposed in order to protect workers, other animals, and the general environment. In other words, "containment" equates to "keep in." The hazardous agents may be biological, chemical, or radiological. Like a "barrier," "containment" can be achieved at the cage level, the room level, an area within an animal facility, or it can be the entire facility, all of which when used together can be considered to provide increasing levels of containment. Figure 8.7 is a schematic of a flexible containment facility designed for containment of all three classes of hazardous agents. The design features of a containment facility are similar to a barrier facility. At all levels of containment, the primary objective is to contain the hazardous agent as close to the source as possible, ideally, at the cage level, e.g., a microisolation cage. Animal cubicles are particularly well suited for use in containment facilities. Of course, the more levels of containment, the higher the safety level. For example, when using a conventional room, housing experimentally infected mice in a microisolation cage, the cage provides the first level of containment and the room door the second level. If housed in a microisolation cage inside an animal cubicle in an animal cubicle room in a barrier area located inside a larger animal facility, there could be at least five levels of containment — the microisolation cage, the cubicle doors, the cubicle room door, and the two doors of the entry vestibule (Figure 8.7). It is important to provide appropriate laboratory and animal procedure space inside containment facilities to avoid having to remove live animals from the facility.

Biohazard Containment — Microbiological agents are classified into four biosafety levels (BSL) according to the degree of risk to humans (classified by the CDC-NIH in the publication "Biosafety in Microbiological and Biomedical Laboratories"21). They are BSL one to four, with one being agents considered to have very low or no pathogenicity for humans and four being the highest risk level. The same publication describes combinations of laboratory practices and techniques, safety equipment, and facilities required for working with agents and animals in each classification level. When animals are infected with microbial agents, the corresponding facilities and management practices are referred to as animal biosafety levels (ABSL) one to four. Animal studies with BSL-2 agents are relatively common and recently have become more so with the use of viral vectors for gene therapy studies, most of which are classified as BSL-2 agents, even if they are referred to as being "replication deficient."22,23 Animal studies with BSL-3 agents are less common than ABSL-2 studies, however, even research facilities that will never need to support an ABSL-3 study could benefit from having an ABSL-3 facility. Studies with BSL-4 agents are rare and are limited to approximately 20 ABSL-4 facilities in the entire world. Studies with BSL-2 agents can be conducted in conventional animal rooms using appropriate equipment and ABSL-2 practices; however, they are more efficiently and consistently conducted at a higher level of safety in an ABSL-3 facility. The primary reasons is that contaminated cages, supplies, and wastes are autoclaved directly out of the facility, eliminating the time-consuming and potentially hazardous practice of having to bag them before transporting them out of the facility to a remote autoclave. In addition, an ABSL-3 facility is highly desirable for quarantine of rodents infected with adventitious agents, or that are of unknown health status. These agents are not hazardous to humans but have the potential to be devastating for many if not most of the rodent studies in the facility.

ABSL-2 is the highest level of biocontainment that can practically be achieved in a conventional room with appropriate equipment and management practices. An ABSL-3 facility has all the design features of a high-level barrier facility as described above. In fact, infectious containment facilities are often managed as both a barrier and containment facility, in that cages and supplies are autoclaved in and soiled cages and wastes are autoclaved out. ABSL-3 facilities should have ventilated entry and exit vestibules with interlocking doors, an autoclave in the facility, and a hand washing sink in each animal room. In addition, a number of design features are required to facilitate keeping agents in, such as an effective sealed envelope around each room and around the entire facility except for the doors (gasketed doors are not required), and air balancing that directs the movement of air from the least contaminated areas to the most contaminated areas. HEPA filtering of exhaust air is not required but is recommended, not only because it increases the degree of safety, but also because it helps to allay public concerns about the existence of the facility in their neighborhood. Exhaust air filters should be the bag-in, bagout type to facilitate safe replacement of contaminated filters. More details regarding animal biosafety facilities and practices can be found in the literature.21,24-31

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