What are viruses
molecular parasites (no metabolism), smaller than bacteria, genome + capsid + envelope (glycoproteins), no differentiative characteristics
Life cycle
- Virion adsorption to cell surface: tropism, neutralizes antibodies
- Viral penetration of cell surface: endocytosis
- Uncoating of viral genome: capsid is degraded
- Primary transcription (gene expression)
- Replication of viral genome
- Secondary transcription: expression of progeny genomes
- Packaging of progeny genomes
- Release of progeny virions: lipid bilayer
Phenotypic mixing/pseudotype formation
Viruses switching coats
Field/street isolate
Directly from natural host
Methods of controlling viral infection
vaccination (killed, live-attenuated, subunit via recombinant proteins) or antiviral drugs
dsDNA virus families
- Papovarviridae: circular, icosahedral (HPV)
- Poxviridae: large + linear
- Adenoviridae: linear + icosahedral (hepatitis)
- Herpesviridae: linear + icosahedral (herpes, varicella)
- Hepadnaviridae: small + partially dd + icosahedral, replicate using reverse transciptase (Hepatitis B)
ssDNA virus families
- Parvoviridae: small linear + non-segmented + icosahedral (Parvovirus B19)
- Anelloviridae: circular + non-segmented + icosahedra (torqueteno virus)
Positive sense
mRNA goes directly into cell and translated directly
Negative sense
converted to mRNA by RNA polymerase and then translated
Segmented RNA
influenza, 2+ unique segments of nucleic acid, rapid evolution due to re-assortment (why there are new types every year)
Positive sense ssRNA viruses – sub-groups
- Single large polyprotein: cleaved to release smaller enzymatic units (picornaviruses, flaviviruses)
- 2+ polyproteins: togaviruses, astroviruses, caliciviruses
- Numerous protein-coding sub-genomic RNAs from large genome: coronavirus
Positive sense ssRNA viruses (7)
- Picornaviridae: small + survives severe conditions, polio and rhino
- Arteriviridae: vascular lesions, edema
- Togaviridae: arthropod-borne encephalitis, rubella
- Coronaviridae: LARGE, helical, upper and lower RT infections
- Hepeviridae: hepatitis E
- Astroviridae and Callciviridae: gastroenteritis
- Flaviviridae: insect vectors, hepatitis G/C, dengue, yellow fever
Negative-sense RNA viruses (6)
- Paramyxoviridae: upper RT, measles, croup
- Rhabdoviridae: rabies (only virus where post-exposure immunization is helpful)
- Orthomyxoviridae: segmented genome, influenza A/B/C
- Bornaviridae: replicate in nucleus to take advantage of splicing machinery
- Bunyaviridae: hantavirus
- Filoviridae: Ebola
dsRNA virus families
- Reoviridae: rotavirus
- Retroviridae: 2 identical strands of positive-sense mRNA (RNA – DNA – mRNA – Protein), AIDS
Isolating virus families
Labile, symptoms may be from immune system not virus
Cytopathic effect
viral infection causes structural changes of host cell
Serological assays
- Neutralization assay: neutralizing antibodies + virus
- Hemagglutination assay: erythrocytes + virus
- Immunostaining: antisera linked to fluorescent dye
- Enzyme-linked immunosorbent assay (ELISA): capturing virus antibodies on solid surface, expose to substrate for detection
Nucleic acid-based methods advantages
virus unable to be cultured, no antibodies (less $), inactivation of virus, reduced transportation concerns, indicates active infection
