Microbiology of Viruses, Subviral Agents, and Viral Life Cycles

Vocabulary flashcards generated from lecture notes on viral classification, morphology, replication cycles, diagnostic assays, and subviral agents.

Chamberland Filter

A porcelain filter invented in 1884 with a pore size of $0.1\,\mu m$ capable of removing all bacterial cells ($\ge 0.2\,\mu m$) from liquid samples.

Dmitri Ivanovski

Russian botanist who in 1892 discovered that passing Tobacco Mosaic Disease extract through a Chamberland filter did not remove the infectious agent, making him a founder of virology.

Martinus Beijerinck

Dutch scientist who in 1899 concluded the Tobacco Mosaic Disease agent was a biological liquid poison, introducing the term virus (Latin for poison).

Wendell Stanley

Scientist who first crystallized Tobacco Mosaic Virus (TMV) structure in 1935 and later isolated Influenza B virus in 1943.

Virion

A complete, newly assembled infectious viral particle that transports the viral genome to new host cells to initiate subsequent infection cycles.

Obligate Intracellular Parasites

Pathogens that lack cellular replication machinery and metabolic genes, relying entirely on exploiting host cell genomes and organelles to replicate.

Bacteriophages

Viruses that specifically infect bacterial cells (also termed phages).

Mechanical Transmission

Mode of vector transmission where an arthropod carries a viral pathogen externally on its body and transfers it to a host via physical contact.

Biological Transmission

Mode of vector transmission where an arthropod harbors a pathogen internally and transmits it to a host via biting.

Zoonoses

Infectious diseases naturally transmitted from animal hosts to humans.

Reverse Zoonoses

Infectious diseases transmitted from human hosts to animals.

International Committee on Taxonomy of Viruses (ICTV)

Organization mandated by the IUMS that classifies viruses into 7 orders, 96 families, and 350 genera based on genetics, chemistry, morphology, and multiplication mechanisms.

Baltimore Classification System

Viral classification system that categorizes viruses into 7 distinct groups based on genome structure ($\text{ssDNA}$, $\text{dsDNA}$, $\text{ssRNA}$, $\text{dsRNA}$) and mode of replication.

International Classification of Diseases (ICD)

Alphanumeric coding system maintained by WHO that assigns codes of up to six characters to verify care, code insurance claims, track mortality, and order lab tests.

Capsid

The protective protein coat surrounding a virus's internal nucleic acid core, built from interlocking subunits called capsomeres.

Capsomeres

Individual protein subunits that interlock to form the outer viral capsid.

Naked Viruses

Nonenveloped viruses consisting solely of a nucleic acid genome enclosed within a protein capsid.

Enveloped Viruses

Viruses featuring a capsid wrapped in a lipid bilayer acquired by budding from host nuclear, organelle, or cytoplasmic membranes.

Viral Spikes

Glycoprotein structures extending outward from a viral capsid or envelope that facilitate attachment and host cell entry.

Hemagglutinin (H) Spikes

Surface glycoprotein spikes on Influenza virus that enable viral attachment to host cell receptors.

Neuraminidase (N) Spikes

Enzymatic glycoprotein spikes on Influenza virus that allow detachment and release of progeny virions from host cells.

Helical Capsid

Cylindrical or rod-shaped viral capsid morphology where capsomeres fit tightly around a spiral nucleic acid core.

Polyhedral Capsid

Three-dimensional, 20-sided viral structure featuring 12 vertices (also called icosahedral).

Lytic Cycle

Bacteriophage replication process performed by virulent phages resulting in host cell lysis and death.

Lysogenic Cycle

Bacteriophage life cycle performed by temperate phages where viral DNA integrates into the host chromosome without causing immediate cell destruction.

Prophage

Phage DNA that has integrated into a host bacterial chromosome during lysogeny.

Lysogen

An infected bacterial cell harboring an integrated prophage genome.

Lysogenic Conversion

The alteration of host bacterial phenotype brought about by expressing foreign genes carried inside an integrated prophage.

Prophage Induction

The process where environmental stress triggers excision of a prophage from the host chromosome, initiating the lytic cycle.

Generalized Transduction

Transfer of bacterial DNA during the lytic cycle when random host chromosomal fragments are mistakenly packaged into phage heads instead of viral DNA.

Specialized Transduction

Transfer of host bacterial DNA occurring at the end of a lysogenic cycle when imprecise prophage excision packages adjacent host genes into new virions.

Tissue Tropism

The specificity of a virus for infecting particular host species, tissues, or specific cell types.

Reverse Transcriptase

Viral enzyme supplied by retroviruses to synthesize single-stranded complementary cDNA from a $+\text{ssRNA}$ genome.

Provirus

Animal viral DNA integrated into a host genome that, unlike a prophage, remains permanently integrated without undergoing excision.

Latent Infection

Persistent viral infection where the virus remains hidden or dormant inside host cells without actively replicating.

Chronic Infection

Persistent infection characterized by continuous, ongoing viral production and recurrent clinical symptoms over extended periods.

Eclipse Phase

Phase in a viral growth curve during penetration and uncoating when free infectious virions cannot be detected in the culture medium.

Burst Phase

Stage in a one-step viral growth curve marked by simultaneous host cell lysis and a rapid rise in viral titer.

Burst Size

The maximum yield of infectious virions produced per individual host cell.

Viral Plaques

Clear, visible zones formed on a bacterial lawn in soft agar where lytic bacteriophages have destroyed host cells.

Primary Cell Culture

Cell culture prepared directly from minced animal tissue organs that displays anchorage dependence and contact inhibition.

Contact Inhibition

Cellular property where cell-to-cell physical contact stops mitotic cell division.

Continuous Cell Lines

Immortal cell cultures derived from transformed cells or tumors that lack contact inhibition and divide indefinitely.

Cytopathic Effects (CPEs)

Observable microscopic cellular abnormalities resulting from viral infection.

Direct Hemagglutination Assay

Serological assay where viral hemagglutinin spikes bind red blood cells to form a visible clumped lattice structure in well plates.

Hemagglutination Inhibition (HAI) Assay

Indirect serological assay where antibodies neutralize viral hemagglutinins, preventing erythrocyte clumping and producing a distinct red dot at the bottom of the well.

Viroids

Acellular plant pathogens discovered by Theodor Diener consisting solely of a short strand of circular single-stranded RNA ($\text{ssRNA}$) without a protein coat.

Virusoids

Subviral non-self-replicating circular $\text{ssRNAs}$ with ribozyme activity that require coinfection with a helper virus to replicate.

Prions

Proteinaceous infectious particles lacking nucleic acids that induce normal cellular proteins ($\text{PrP}^C$) to misfold into rogue forms ($\text{PrP}^{\text{Sc}}$).

Transmissible Spongiform Encephalopathies (TSEs)

Fatal neurodegenerative brain diseases caused by prions that produce sponge-like brain lesions, severe dementia, and motor loss.