Animal Viruses, Prions, and Viroids

Comprehensive vocabulary flashcards reviewing animal virus structures, viral multiplication cycles, HIV and coronavirus pathogenesis, cultivation strategies, and nonviral submicroscopic agents like prions and viroids.

Icosahedral Capsid

A regular geometric viral capsid consisting of $20$ equilateral triangular faces, $30$ edges, and $12$ vertices, constructed from a minimum of $60$ capsomeres (with larger viruses possessing multiples such as $120$, $240$, or $360$).

Helical Capsid

A spiral-shaped protein capsid constructed from repeating protein subunits termed protomers that coil around a central strand of nucleic acid.

Reverse Transcriptase

A viral core enzyme found in retroviruses like HIV that synthesizes a complementary DNA strand from a viral RNA template.

Neuraminidase

A viral core enzyme that breaks down the glycosidic bonds of host surface glycolipids and glycoproteins during infection and viral release.

Lysozyme

An enzyme carried by certain viruses that breaks down bacterial cell walls to produce holes for nucleic acid injection or host lysis.

Adsorption

The initial multiplication phase wherein a virus collides coincidentally with a susceptible host cell and specifically binds to host surface receptors via viral surface molecules or spikes.

Host Range

The specific spectrum of host cells that a virus is capable of infecting, dictated by surface receptor compatibility (e.g., Hepatitis B infecting human liver cells, Poliovirus infecting primate intestinal and nerve cells).

Membrane Fusion

An entry mechanism exhibited by enveloped viruses where the viral envelope merges directly with the host cell cytoplasmic membrane via lipid rearrangement, discharging the nucleocapsid directly into the cytoplasm.

Endocytosis (Viral Entry)

A mode of viral penetration where the host cell engulfs an entire enveloped or naked virion into a vesicle or endosome, followed by vesicle fusion and uncoating.

Positive-Sense RNA

Single-stranded viral RNA genomes that already contain the correct message sequence to be translated directly into viral proteins by host ribosomes.

Negative-Sense RNA

Single-stranded viral RNA genomes that cannot be directly translated and must first serve as a template to synthesize a complementary positive-sense RNA strand.

Cytopathic Effects (CPE)

Virus-induced microscopic damage visible in host cells, including cell disorientation, gross alterations in shape or size, and intracellular formations such as inclusion bodies or syncytia.

Syncytium

A multinucleated giant protoplasmic mass formed by the viral-induced fusion of multiple adjacent host cell membranes during cytopathic infection.

Budding (Exocytosis)

A gradual release mechanism of enveloped viruses in which the nucleocapsid binds to the host membrane and extrudes, acquiring a host-derived lipid envelope and matrix proteins without immediate cell destruction.

Cell Lysis

A nonenveloped and complex virus release pathway in which newly assembled virions are simultaneously freed through the physical rupture and death of the host cell.

Bird Embryo Inoculation

An in vivo cultivation method utilizing intact, self-supporting avian eggs providing sterile environments and embryonic tissue compartments (amniotic cavity, allantoic cavity, embryo, yolk sac, or chorioallantoic membrane) to support viral growth.

Cell (Tissue) Culture

An in vitro cultivation technique using prepared layers of animal host cells to propagate viruses, study viral kinetics, and directly observe cytopathic effects.

Provirus

Viral double-stranded DNA synthesized by reverse transcription that integrates into a host cell chromosome via viral integrase, replicating passively when the host cell divides.

CCR5 Co-receptor

A chemokine coreceptor situated on CD4+ host white blood cells that interacts alongside CD4 with HIV surface spikes; inherited mutations in CCR5 confer natural resistance to HIV infection.

Viral Spillover

The transmission event that occurs through continuous human-animal intermingling when an animal pathogen jumps species barriers to infect human hosts.

Severe Acute Respiratory Syndrome (SARS-CoV)

A coronavirus that emerged in 2002 transmitted via respiratory droplets or direct contact, causing flu-like symptoms, fever, pneumonia, and severe acute respiratory distress.

Middle East Respiratory Syndrome (MERS-CoV)

A pathogenic coronavirus causing localized outbreaks characterized by a high death rate of approximately $34\%$, which exceeds historical smallpox and plague fatality rates.

Angiotensin-Converting Enzyme 2 (ACE2)

The host cell surface receptor that the SARS-CoV-2 spike glycoprotein specifically recognizes and binds prior to membrane fusion and entry.

Cytokine Release Syndrome

A massive, systemic inflammatory reaction caused by rapid hyper-secretion of cytokines during severe SARS-CoV-2 infection, causing acute respiratory distress syndrome and failure of the kidneys, heart, and liver.

Influenza Virus Anatomy

An enveloped RNA virion displaying surface Hemagglutinin spikes, Neuraminidase (Sialidase) spikes, a surrounding lipid envelope, an internal capsid, and segmented nucleoprotein RNA.

Coronavirus Spike Glycoprotein (S)

A prominent viral envelope surface protrusion responsible for attachment to specific host cell receptors, providing the distinctive crown-like appearance in coronaviruses.

Prions

Acellular, proteinaceous infectious agents containing no nucleic acid that induce normal host proteins to shift conformation into pathogenic prions, forming tight, elongate fibrillar aggregates that destroy nerve cells.

Transmissible Spongiform Encephalopathies (TSE)

Fatal, chronic neurodegenerative disorders caused by prions; includes scrapie in sheep/goats, bovine spongiform encephalopathy (BSE) in cattle, wasting disease in elk, and Creutzfeldt-Jakob Syndrome (CJS) in humans.

Satellite Viruses

Defective subviral particles dependent on helper viruses for replication, such as adeno-associated virus (dependent on adenovirus) and the Delta agent (expressed only in the presence of hepatitis B virus).

Viroids

Infectious plant pathogens composed strictly of naked, short single strands of circular RNA devoid of any protective capsid or protein coat.