Virology Cheat Sheet

The core ideas of Virology distilled into a single, scannable reference — perfect for review or quick lookup.

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Quick Reference

Viral Structure and Classification

Viruses are classified by their type of nucleic acid (DNA or RNA), capsid symmetry (icosahedral, helical, or complex), presence or absence of an envelope, and replication strategy. The Baltimore classification system groups viruses into seven classes based on how they produce messenger RNA from their genomes.

Viral Replication Cycle

The series of steps by which a virus reproduces inside a host cell: attachment to specific receptors, entry into the cell, uncoating of the nucleic acid, replication of the genome, expression of viral proteins, assembly of new virions, and release by lysis or budding.

Host Immune Response to Viruses

The innate and adaptive immune mechanisms that detect and eliminate viral infections. Innate responses include interferon production, natural killer cell activity, and inflammatory signaling. Adaptive responses involve virus-specific antibodies produced by B cells and cytotoxic T lymphocytes that kill infected cells.

Antigenic Drift and Shift

Antigenic drift refers to gradual accumulation of mutations in viral surface proteins through replication errors, while antigenic shift involves the sudden reassortment of genome segments between different viral strains, producing a dramatically different surface antigen profile.

Vaccines and Vaccination

Biological preparations that stimulate the immune system to recognize and fight specific viruses. Types include live-attenuated vaccines, inactivated vaccines, subunit vaccines, viral vector vaccines, and nucleic acid vaccines (mRNA and DNA). Vaccines have eliminated or controlled many viral diseases.

Zoonotic Spillover

The transmission of a virus from an animal reservoir to humans, often facilitated by ecological disruption, close human-animal contact, or intermediate hosts. Most emerging infectious diseases are zoonotic in origin, making wildlife surveillance critical for pandemic preparedness.

Antiviral Drug Mechanisms

Pharmacological agents that target specific stages of the viral replication cycle. Classes include entry inhibitors, polymerase inhibitors, protease inhibitors, integrase inhibitors, and neuraminidase inhibitors. Unlike antibiotics, antivirals are typically virus-specific.

Viral Evolution and Quasispecies

RNA viruses exist as diverse populations of closely related genetic variants called quasispecies rather than single defined sequences. High mutation rates, short generation times, and large population sizes drive rapid evolution, enabling adaptation to new hosts, immune evasion, and drug resistance.

Bacteriophages

Viruses that specifically infect bacteria. Phages are the most abundant biological entities on Earth and play critical roles in microbial ecology, horizontal gene transfer, and the regulation of bacterial populations. They are also being explored as alternatives to antibiotics in phage therapy.

Viral Oncogenesis

The process by which certain viruses contribute to the development of cancer by inserting oncogenes into the host genome, inactivating tumor suppressor genes, or causing chronic inflammation. Approximately 15-20% of human cancers are associated with viral infections.

Key Terms at a Glance

Attachment:The first step of viral infection in which the virus binds to specific receptors on the host cell surface.

Budding:A process by which enveloped viruses exit the host cell by wrapping themselves in a portion of the cell membrane.

Capsomere:An individual protein subunit that assembles to form the viral capsid.

Cytokine Storm:An excessive, uncontrolled release of pro-inflammatory cytokines triggered by infection, which can cause severe tissue damage and organ failure.

Eclipse Period:The phase in the viral replication cycle after uncoating when no complete virions are detectable inside the host cell.

Endocytosis:A cellular process used by some viruses to enter host cells by being engulfed in a membrane-bound vesicle.

Genome Reassortment:The exchange of genome segments between two related viruses co-infecting the same cell, leading to novel viral combinations.

Glycoprotein:A protein with attached carbohydrate groups, often found on viral envelopes where it mediates attachment and entry into host cells.

Inclusion Body:Abnormal structures within host cells formed during viral infection, consisting of viral particles or components. Used as diagnostic markers.

Latency:A state in which a virus persists in the host cell without active replication, potentially reactivating later (e.g., herpesviruses).

Multiplicity of Infection (MOI):The ratio of infectious viral particles to target cells in a given infection experiment.

Neutralizing Antibody:An antibody that binds to a virus and prevents it from infecting host cells, typically by blocking attachment or entry.

Oncovirus:A virus that can cause cancer by disrupting normal cell growth regulation, such as HPV, HBV, or EBV.

Pandemic:A global outbreak of an infectious disease affecting a large proportion of the population across multiple countries or continents.

Plaque Assay:A laboratory technique used to quantify infectious virus by counting clear zones (plaques) formed on a cell monolayer.

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