virology lec. 2 virus architecture & nomenclature

Discovery of new viruses increasing rapidly in 21st century thu…

Metagenomics, next generation sequencing (NGS), and bioinformatics

Metagenomics

Study if genetic material directly from environmental samples

Zoonosis

Diseases transmitted to humans from animals- trafficking of bushmeat, bioterrorism, climate change

Why are virus particles formed?

Protection, recognition, self-assembly, fidelity, and economy

Protection

The unprotected viral genome is sensitive to physical damage

Recognition

The outer surface of the virus particle is involved in the recognition and attachment to the host cell

Self-assembly

The spontaneous formation of protein shell around the viral genome

Fidelity

The particle composition is of high fidelity in terms of precision and accuracy

Economy

An icosahedron is a geometric figure that approaches a sphere in shape. The latter has the most volume for the least amount of surface area.

Stability

Virus particles composed of subunits.

Subunit- single folded polypeptide chain

Capsomers- repeating protein subunits

Viral shapes

Icosahedral (poliovirus)

Helical rod or cylinder shape (VSV is enveloped and helical in shape)

Complex is less common

- characteristic of larger viruses (poxviruses)

Naked viruses

Such as noroviruses (absence of envelope)- more stable in the environment)

Hand sanitizer don’t kill cuz covered in organic matter like vomit or fecal

Ex. Polio (stomach) virus.

Enveloped viruses

Such as influenza virus, HSV & HIV

• lipid bilayer stolen from host cell

• Spherical and helical types

• Can be killed w/ alcohol

Viral genomes

• single stranded (ss) or double stranded (ds)

• Linear or circular

• Monopartite= non segmented genome. Ex; polio,HIV, smallpox

• Multipartite= segmented genome. Ex; influenza virus 3

Viruses that challenge the definition of a virus

Viruses and virophages

Giruses

“Giant” DNA-containing viruses.

• Mimivirus

• Mamavirus

Sometimes for vaccine

Virophages

Subviral agents within other big viruses

• Sputnik- uses the helper virus’s machinery for reproduction and inhibits replication of the helper virus

Taxonomy: what’s in a name?

• early discovery of viruses based on size of infectious agent

• Early attempts to classify viruses were thus based only on size

• Modern research has revealed genetic differences

• Tools:

- porcelain chamberland filter

- electron microscopy

Origin of virus names

Historically, viruses named after:

• diseases the virus caused

• Morphological characteristics

• Places viruses first isolated

• Virus discoverers

• Acronyms

The race to characterize SARS-CoV

• Atypical pneumonia in Hanoi, Vietnam (2003)

• SARS-CoV causes rapidly spreading, highly contagious

respiratory disease

• Dr. Carlo Urbani (infectious diseases specialist who died

from SARS-CoV infection.

How are viruses classified?

Baltimore classification by David Baltimore

• 7 classes based on type of nucleic acid:

dsDNA viruses

ssDNA viruses

dsRNA viruses

+ssRNA viruses

-ssRNA viruses

RNA reverse-transcribing viruses

DNA reverse-transcribing viruses

The International Committee on Taxonomy of Viruses (ICTV)

• charged with developing a universal taxonomic scheme to name and classify viruses

• ICTV database

• Based on physical and chemical properties

- order (-virals)

- family (-viridae)

- subfamily (-virinae)

- Genus (-virus)

- species

Additional lower hierarchical levels

Species

• polythetic class

Strain

• different isolates of same virus

Variant

• differs from original wild-type strain

What is a syndrome?

Sets of physical signs and symptoms that occur together