This is a concise and quick reference guide, clinically oriented, based on experience underpinned by published research data. The systems-based approach emphasizes the problem list process utilized by most practitioners when faced with a patient presenting with a single or variety of clinical symptoms. This allows generation of a complete list of infectious disease differentials, and the ability to include or exclude those indicated based on patient risk assessment. Pathogen specific information enables rational choice of diagnostics, therapy, and prognostication for a complete list of small animal infectious disease that includes bacterial, viral, parasitic/protozoal and fungal.