What is the term for an individual virus particle?

The term for an individual virus particle is "virion." A virion is a complete, infective form of a virus outside of a host cell, consisting of genetic material—either DNA or RNA—encased in a protein coat called a capsid, and sometimes surrounded by an additional lipid envelope.

Understanding this term is essential in virology as it distinguishes between the viral particle as it exists in isolation and the broader virus, which may refer to the entire entity including its modes of replication, life cycle, and infection mechanisms. This precision helps in the study of viral behavior, pathology, and treatment strategies.

The other terms listed describe different biological agents: a bacteriophage specifically refers to a virus that infects bacteria, while a prion is an infectious protein that can cause neurodegenerative diseases. These distinctions highlight the unique characteristics and structures of various pathogens, underscoring the importance of accurate terminology in the field of veterinary medicine and microbiology.