Filter Top Cages and Individually Ventilated Cage Systems IVC

In some cases, it may be practical or economical to place the barrier around the individual cage rather than the entire unit. This principle may be used inside a barrier-protected unit to enhance the protection of the individual animal or as an alternative to running such a facility. The simplest principle is to place a lid on the cage. This lid, called a filter-top, is provided with a filter to allow the passage of the air (Figure 11.10). The system is also called a "microisolator," but although these filter-tops may be more or less sealed to the cage, they cannot be regarded as isolation. The risk for spreading infections as well as allergens may be reduced, but certainly not eliminated. Occasionally, concentrations of trace gases in a filter-topped cage may be elevated,224 which may be hazardous to the animals.243 In individually ventilated cage (IVC) systems (Figure 11.11), each filter-topped cage is supplied with its own ventilation, and all cages are isolated from one another as well as the surroundings. Principles and degrees of sealing depend on the brand of the system. This allows the microbiological separation of each individual cage,

thereby isolating the animals not only from the surroundings, but also from one another. To allow the continued separation, cages are changed in a specially equipped laminar airflow system. Some IVC systems may be run at positive and negative pressures.

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