Medical Virology: Viral Classification, Genome Structure, and Pathogenesis

Comprehensive vocabulary flashcards summarizing viral characteristics, genome types, capsids, envelopes, replication sites, sites of damage, and clinical manifestations across major DNA and RNA virus families.

Orthomyxoviruses

A family of pleomorphic enveloped viruses with a segmented ($8\text{ ssRNA-}$ segments) genome and helical nucleocapsid; replicates in the nucleus and causes influenza (the flu) in the respiratory tract.

Morbillivirus (Measles)

A pleomorphic enveloped paramyxovirus containing a large linear ssRNA (-) genome and helical nucleocapsid; replicates in the cytoplasm and causes primary damage to the respiratory tract ($1^\circ$) followed by a widespread, maculopapular rash.

Paramyxovirus (Mumps / Parainfluenza)

A pleomorphic enveloped virus possessing a large linear ssRNA (-) genome and helical nucleocapsid; replicates in the cytoplasm, targeting the respiratory tract ($1^\circ$) and secondary sites such as the parotid gland ($2^\circ$).

Pneumovirus (RSV / Metapneumovirus)

A paramyxovirus with a pleomorphic enveloped structure, large linear ssRNA (-) genome, and helical nucleocapsid; replicates in the cytoplasm and primarily damages the respiratory tract ($1^\circ$), causing pneumonia.

Rhinoviruses

Naked picornaviruses possessing a small linear ssRNA (+) mRNA genome and icosahedral capsid; replicate in the cytoplasm, infect the respiratory tract, and are the #1 cause of the common cold.

Picornaviruses (Non-Respiratory)

A family of naked viruses with small linear ssRNA (+) mRNA genomes and icosahedral capsids that replicate in the cytoplasm; members include Poliovirus, Coxsackie, and Echovirus (CNS, meningitis), Coxsackie (Heart, myocarditis), Echovirus and Coxsackie (Skin, Foot and mouth disease, rash), and Hepatovirus (Liver, hepatitis).

Coronaviruses

Enveloped virions with a helical nucleocapsid and ssRNA (+) helical genome; replicate in the cytoplasm and target the upper respiratory tract, causing the common cold (#2 cause), severe respiratory disease, and COVID-19 (SARS, MERS, SARS CoV2).

Adenoviruses

Naked viruses characterized by linear dsDNA and an icosadeltahedral capsid; replicate in the nucleus across many serotypes, damaging the respiratory tract, eye, and GI tract to cause laryngitis, conjunctivitis, gastroenteritis, and bronchiolitis.

Rubella virus (Togaviruses)

An enveloped togavirus with a linear ssRNA (+) genome and icosahedral capsid; replicates in the cytoplasm and damages the upper respiratory tract, causing German measles (macular rash).

Alpha Herpesviruses (HSV-1, HSV-2, VZV)

Viral glycoprotein-rich enveloped viruses with linear dsDNA and icosadeltahedral capsids replicating in the nucleus; establish latency in ganglia (HSV-1: trigeminal ganglion; HSV-2: sacral ganglion; VZV: dorsal root ganglion) and cause fever blisters, genital herpes, chickenpox, and shingles.

Beta Herpesviruses (CMV, HHV 6 & 7)

Viral glycoprotein-rich enveloped dsDNA viruses with icosadeltahedral capsids replicating in the nucleus; establish latency in immune cells (CMV in B & T cells; HHV-6/7 in T cells) and cause mononucleosis, pneumonia, and Roseola (HHV-6).

Gamma Herpesviruses (EBV, HHV-8)

Viral glycoprotein-rich enveloped dsDNA viruses with icosadeltahedral capsids replicating in the nucleus; establish latency in B cells and cause infectious mononucleosis, B cell tumors (EBV), and Kaposi sarcoma (HHV-8).

Hepatitis A Virus (HAV)

A naked picornavirus with a linear ssRNA (+) genome and icosahedral capsid; replicates in the cytoplasm and damages hepatocytes, causing acute hepatitis.

Hepatitis B Virus (HBV)

An enveloped hepadnavirus containing an incomplete dsDNA genome (Dane particle) and icosahedral capsid; replicates in the nucleus (via host polymerase) and cytoplasm (via reverse transcriptase), causing acute and chronic hepatocyte damage.

Hepatitis C Virus (HCV)

An enveloped flavivirus containing a linear ssRNA (+) genome and icosahedral capsid; replicates in the cytoplasm, buds from the ER, stays inside the cell, and causes acute and chronic hepatitis.

Hepatitis D Virus (HDV)

An enveloped delta virus with a circular ssRNA (-) genome and icosahedral capsid; requires HBV coinfection to replicate and produces acute and chronic hepatocyte damage.

Hepatitis E Virus (HEV)

A naked, calicivirus-like virus possessing a linear ssRNA (+) genome and icosahedral capsid; replicates in the cytoplasm and targets hepatocytes.

Rotaviruses

Naked viruses possessing an icosahedral double-layered capsid and a segmented ($11$ segments) dsRNA genome; replicate in the endosome/ER and cause intestinal damage leading to diarrhea.

Calicivirus (Norovirus)

A naked virus featuring a linear ssRNA (+) genome and icosahedral capsid; replicates in the cytoplasm and infects the intestine to cause diarrhea.

Astrovirus

A diarrhea-causing virus with a distinctive star-shaped capsid and linear ssRNA (+) genome; replicates in the cytoplasm and damages the intestine.

Rabies Virus

A bullet-shaped enveloped virus with a helical nucleocapsid and ssRNA (-) genome; replicates initially at the site of the bite and damages the brain (encephalitis), with subsequent dissemination to the eye, skin, and glands.

Retroviruses

Enveloped viruses (including HTLV 1-2 oncoviruses and HIV 1-2 lentiviruses) with A–D type nucleocapsids and an ssRNA (+) genome replicating via a DNA intermediate in the nucleus; specifically target and damage the immune system.

Papillomaviruses (HPV)

Naked dsDNA viruses with a circular genome and icosahedral capsid that replicate in the nucleus; infect skin, mucosa, and the urogenital tract to cause skin warts (HPV 1–4, 7, 10), genital warts (HPV 6, 11), and cervical cancer (HPV 16, 18).

Polyomaviruses (JK & BK virus)

Naked dsDNA viruses with a circular genome and icosahedral capsid that replicate in the nucleus; includes BK virus and JK virus, the latter of which causes progressive multifocal leukoencephalopathy (PML).

Viral Attachment Proteins (VAPs)

Specific viral surface proteins that bind to host cellular receptors to mediate viral entry; examples include the Spike protein (Coronaviruses) and Hemagglutinin (Orthomyxoviruses/Influenza).

Viral Host Receptors

Host cell surface receptors recognized by viral attachment proteins for cell entry; examples include ICAM, the Adenovirus coxsackie complex, and acetylcholine receptors (AChR).

Viral Polymerases

Enzymes essential for viral nucleic acid replication and transcription; examples include viral RNA polymerase (used by RNA viruses) and reverse transcriptase (RT) (used by retroviruses and HBV).