The health status of the animal is also important since outbreaks of disease can have devastating effects both on programs of research, breeding programs, and on animal welfare (Mansfield et al, 20101). To reduce the risk of disease, most animal facilities maintain a number of barriers to prevent the introduction of infectious diseases. These will normally include control of access to the facility, use of appropriate protective clothing and equipment, incorporation of sterilisation or disinfection of cages, diet and bedding, and other measures to avoid the introduction of potentially contaminated equipment. The air supply to the unit may be filtered, and physical barriers will be in place to prevent the entry of wild rodents or birds. Cell lines and other tissue (eg tumour fragments) can be a source of pathogens, and units may require screening of this material to ensure it is free from infectious agents.