Virology Summary Lecture

Comprehensive vocabulary flashcards covering the structural characteristics, classification, replication mechanisms, diagnostic methods, and clinical relevance of key DNA and RNA viruses.

Viruses

Obligate intracellular infectious agents that lack ribosomes and independent metabolism, requiring living host cells to produce new virions.

Virion

A complete infectious particle consisting of a viral genome (DNA or RNA) and a protein capsid, with or without a lipid envelope, that is assembled rather than dividing by binary fission.

Capsid

A protein shell that protects the viral genome; in naked viruses, exposed capsid proteins recognize host receptors and serve as important antigens.

Viral Envelope

A host-derived lipid membrane containing viral glycoproteins (spikes) that are required for attachment and/or fusion in enveloped viruses.

Viral Variant

A virus exhibiting genetic changes compared with other circulating viruses, which may affect transmissibility, immune recognition, or pathogenicity.

Genotype (Viral)

Viral classification based on differences in the nucleotide sequences of the viral genome.

Serotype (Viral)

Viral classification based on antigenic differences recognized by the immune system, particularly by antibodies.

Quasispecies

A population of closely related viral genetic variants produced during replication, especially in RNA viruses, that facilitates adaptation and selection.

Naked (Non-Enveloped) Viruses

Viruses possessing only an external protein capsid, rendering them generally more resistant to drying, acids, and detergents; they often spread via fecal-oral routes or fomites and typically exit cells via lysis.

Enveloped Viruses

Viruses enclosed in a lipid membrane that is easily damaged by detergents, alcohol disinfectants, and desiccation; they usually spread by respiratory secretions, blood, close contact, or sexual exposure and tend to exit cells via budding or secretion.

Viral Tropism

The preference of a virus for particular host species, organs, tissues, or cell types, primarily determined by viral surface proteins binding compatible cellular receptors.

Hemagglutinin (H)

An influenza viral surface glycoprotein that binds sialic acid receptors on respiratory epithelial cells to mediate attachment and infection.

Neuraminidase (NA)

An influenza viral surface enzyme that helps release newly assembled virions from host cells.

gp120

An HIV envelope glycoprotein that binds to CD4 receptors on susceptible host T cells to facilitate infection.

Spike (S) Glycoprotein

A SARS-CoV-2 surface glycoprotein that binds to the ACE2 receptor (along with entry cofactors) to mediate viral entry.

Positive-Sense RNA (+ssRNA)

Viral single-stranded RNA that can function directly as mRNA to be translated by host ribosomes immediately upon entry into the cell.

Negative-Sense RNA (−ssRNA)

Viral single-stranded RNA that must first be transcribed into positive-sense mRNA by an RNA-dependent RNA polymerase carried inside the virion.

Poxviruses

A notable exception among DNA viruses because they replicate within the host cell cytoplasm rather than inside the nucleus.

Reverse Transcriptase

An enzyme that transcribes an RNA template into complementary DNA, utilized by retroviruses like HIV and during the replication cycle of hepatitis B virus.

cccDNA (Covalently Closed Circular DNA)

A stable nuclear form of the hepatitis B virus DNA genome from which pregenomic RNA and viral mRNAs are transcribed.

Cytopathic Effects (CPE)

Visible structural and morphological abnormalities in host cells or tissues caused by viral infection, such as cell lysis, intracellular inclusions, or multinucleated syncytia formation.

Adenovirus

A naked dsDNA virus that replicates in the nucleus, binds receptors on multiple cell types (broad tropism), and causes respiratory infections, keratoconjunctivitis, and childhood gastroenteritis.

Human Papillomavirus (HPV)

A naked circular dsDNA virus that infects basal epithelial cells through cutaneous or mucosal micro-abrasions.

HPV 6 and 11

Low-risk, non-oncogenic HPV types responsible for benign epithelial proliferations, notably most cases of genital warts.

HPV 16 and 18

High-risk, oncogenic HPV types responsible for the majority of HPV-associated cervical cancers, as well as anal, penile, vulvar, and oropharyngeal cancers.

E6 and E7

Viral oncoproteins of high-risk HPV that interfere with host tumour-suppressor proteins to promote uncontrolled cell proliferation.

Herpesviruses

A family of enveloped dsDNA viruses characterized by the ability to establish lifelong latency within host cells with potential for reactivation.

HSV-1 and HSV-2

Enveloped dsDNA viruses that infect epithelial cells and establish latency in sensory neurons; HSV-1 is typically associated with oral herpes, while HSV-2 is more frequently associated with genital herpes.

Varicella-Zoster Virus (VZV)

An enveloped dsDNA herpesvirus that causes chickenpox upon primary infection, remains latent in sensory ganglia, and can reactivate as shingles (herpes zoster).

Epstein–Barr Virus (EBV)

An enveloped dsDNA herpesvirus transmitted via saliva that infects epithelial cells and B lymphocytes, establishing latency in B cells; it causes infectious mononucleosis and is linked to Burkitt lymphoma and nasopharyngeal carcinoma.

Cytomegalovirus (CMV)

An enveloped dsDNA herpesvirus that establishes latency in myeloid lineage cells, frequently causing severe disease in immunocompromised patients, transplant recipients, and congenitally infected fetuses.

Hepatitis B Virus (HBV)

An enveloped, partially double-stranded circular DNA virus that replicates through an RNA intermediate using reverse transcriptase and can lead to acute or chronic hepatitis, cirrhosis, and hepatocellular carcinoma.

Hepatitis D Virus (HDV)

A defective RNA virus that requires hepatitis B virus surface proteins to complete its life cycle and is therefore preventable via HBV vaccination.

Norovirus

A naked +ssRNA virus with high environmental stability and a low infectious dose that causes acute gastroenteritis outbreaks in crowded closed environments like cruise ships and hospitals.

Rotavirus

A naked, segmented dsRNA virus (11 segments) with a low infectious dose that causes severe dehydrating diarrhea and vomiting in infants and young children.

Hepatitis A Virus (HAV)

A naked +ssRNA virus transmitted via the fecal–oral route that causes acute hepatitis and does not cause chronic infection.

Hepatitis C Virus (HCV)

An enveloped +ssRNA virus transmitted primarily through blood exposure that frequently begins asymptomatically and has a high propensity to cause chronic hepatitis, cirrhosis, and hepatocellular carcinoma.

Antigenic Drift

The gradual accumulation of point mutations in viral surface antigens (such as influenza hemagglutinin and neuraminidase) that produces seasonal variants requiring vaccine reformulation.

Antigenic Shift

The major antigenic variation resulting from the reassortment of complete genome segments between different influenza A viruses, which can trigger pandemics.

Undetectable = Untransmittable (U=U)

The clinical reality that individuals living with HIV who maintain a sustained undetectable viral load through antiretroviral therapy cannot sexually transmit the virus to others.