_____A single virion is sufficient to cause a cold.

Verified step by step guidance

1. Understand the term 'virion': A virion is a complete virus particle that consists of an RNA or DNA core with a protein coat and is the extracellular infective form of a virus.
2. Recognize the infectious dose concept: The infectious dose is the number of virions required to establish an infection in a host.
3. Consider the nature of the common cold virus (usually rhinovirus): It is known for its high infectivity, meaning very few virions are needed to cause infection.
4. Analyze the statement: 'A single virion is sufficient to cause a cold' implies that even one virus particle can initiate infection, which relates to the minimal infectious dose.
5. Conclude that the statement is about the minimal infectious dose and the high infectivity of cold viruses, emphasizing that sometimes even one virion can start the infection process.

Key Concepts

Virion and Virus Structure

A virion is the complete, infectious form of a virus outside a host cell, consisting of genetic material enclosed in a protein coat. Understanding the virion's structure helps explain how viruses infect host cells and initiate disease.

Infectious Dose

The infectious dose is the minimum number of viral particles required to establish an infection. Some viruses, like those causing the common cold, can cause infection with very few virions, sometimes even a single one.

Pathogenesis of the Common Cold

The common cold is caused primarily by rhinoviruses, which infect the upper respiratory tract. Their ability to cause infection from a low number of virions is linked to their rapid replication and evasion of the immune response.