There are four levels for experimental animal in accordance with microbiological control standards:
Level I: Common animals(CV) are general animals that are not subject to special control. They are required not to have the pathogen and for main infectious diseases for human and animal diseases and pathogen for fulminating infectious disease. In order to prevent infectious disease, it is necessary to take certain measures to ensure reproducibility of the results of the experiment during animal breeding (The experiments carried out by different operators and in different time in accordance with experimental procedures on same type of animals should have similar results).
Level II: Clean animal (CL) are required not to have the pathogen for main infectious diseases for human and animal diseases.
Level III: Animals without special pathogen (SPF) are required to reach level II and exclude some designated pathogen. Hign effciency air filter sterilization, three glycol vapor spray and aqueous solution of lithium chloride spray can be used for sterilization.
Level IV: Sterile animal (GF) or gnotobiotic animal (GN). Sterile animals are required not to have any mircroorganisms that can be detected by existing method. Gnotobiotic animals are required not have implanted with one or several kinds of known microorganisms in the sterile animal.
