This episode explores the picornaviruses, a large family of small, non-enveloped, positive-sense single-stranded RNA viruses. Drawing from Murray’s Chapter 46, it examines how genomic efficiency enables extensive clinical diversity.

The family includes:

* Enteroviruses (poliovirus, coxsackieviruses, echoviruses)

* Rhinoviruses

* Hepatitis A virus

The replication strategy is direct and efficient: the positive-sense RNA genome functions immediately as mRNA upon entry into the cytoplasm. Translation produces a single polyprotein that is cleaved into functional viral proteins.

Clinically, picornaviruses demonstrate broad tropism:

* Respiratory infection (rhinovirus - common cold)

* Neurologic disease (poliovirus)

* Myocarditis (coxsackievirus)

* Gastrointestinal illness

* Acute hepatitis (HAV)

Conceptually, these viruses illustrate that small genome size does not limit clinical impact. Environmental resilience due to lack of envelope enhances transmission, particularly via the faecal–oral route.

Key Takeaways

* Picornaviruses are small, non-enveloped positive-sense RNA viruses

* Genome acts directly as mRNA

* Include enteroviruses, rhinoviruses, and HAV

* Broad clinical spectrum

* Transmission often faecal–oral or respiratory

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