Biological agents are micro-organisms, including genetically modified micro-organisms, cell cultures and human endoparasites, which may give rise to infections, allergies or toxic reactions. In accordance with the Regulation relating to Biological Agents (Verordnung biologische Arbeitsstoffe, VbA), biological agents are subdivided into 4 categories depending on their risk potential. The Regulation deals with both the intended use of biological agents (i.e. in laboratories for research and development purposes) and their unintended action (i.e. as a result of air conditioning systems that have never been properly maintained or cleaned).