Virology

In 2020, a novel coronavirus spread across the world, and within weeks, clinical microbiologists had characterised its genome, developed PCR-based diagnostic tests, and begun evaluating serological assays for population-level surveillance. That speed was possible because the foundational principles of virology — viral structure, replication, tropism, and immune evasion — were already understood.

Virology is the study of viruses: obligate intracellular parasites that require a host cell to replicate, cause disease through mechanisms distinct from bacteria or fungi, and pose unique diagnostic challenges because they cannot be grown on standard bacteriological media.

This section covers:

• Viral structure and classification — capsid morphology, envelope composition, genome type (DNA vs. RNA, single- vs. double-stranded, segmented vs. non-segmented), and the Baltimore classification system
• Viral replication — attachment, entry, genome replication, assembly, and release; how antiviral drugs target specific steps in this cycle
• Organism profiles — all major clinically important virus families, including Herpesviridae, Hepatitis viruses, HIV, Influenza, Dengue, Measles, Rabies, HPV, Rotavirus, and others
• Pathogenesis and immune evasion — how viruses cause cell damage, establish latency, and evade host immune responses
• Laboratory diagnosis — cell culture, PCR-based detection, antigen testing, and serology; how to interpret IgM versus IgG results; the role of viral load testing in monitoring

A recurring theme in clinical virology is the interpretation of serological results — understanding that IgM indicates recent infection and IgG indicates past exposure or vaccination, and knowing when those rules have exceptions, is as important as memorising which virus causes which disease.