Viruses~~~ :)

~~**Welcome**~~ :)

.. to our Microbiology B blog on viruses.
This blog will be posts regarding what we've learnt during microbiology B, or more.
We hope to share with you all regarding if what we've learnt, so that everyone knowledge on viruses would increase!

Click:
~1st tab to study more on viruses- introduction
~2nd tab is on what we've learn in lecture
~3rd tab is to watch video

Thanks for reading =) ENJOY

Here are some pictures~~~

Members

♥Eileen Ng Hui Qi
♥Tang Xu Yun
♥Koh Jia Huan
♥Canice Tay

NYP SCL MB0804

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Exclusive design of Little-Miss-Wendy

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● @ Monday, December 15, 2008 ●

Lecture 4!

Picronaviridae

Unique Feature of RNA virus
· All living things have DNA as genetic material
· Only viruses have RNA as genetic material
· Central Dogma—from DNA to RNA to Protein
· Genome is infectious ( + RNA viruses)
· Unusual structural characteristic (leader sequence)
· Differentiate between viral mRNA and host mRNA

Picornaviridae- the largest virus family
Virus
· Aphtovirus
· Cardiovirus
· Enterovirus
· Heptovirus
· Rhinovirus

3D structure of Enterovirus and Rhinovirus

Morphology
· Virions (naked)
· Nucleocapsid
· Incomplete or empty capsids commom

Genome
· One linear (+) RNA- infectious
· Long untranslated region of 5’ end “clover leaf” structure(IRES)
· Single polyprotein of 2100-2400 aa
· Both ends modified

Disease caused
· Enterovirus—Hand-Foot Mouth Disease
· Rhinovirus-- Common flu

commonn cold virus

Pathogenesis
· Upper respiratory tract infection
· Short incubation (2-3 days)

Symptoms

· Rhinovirus- Cold:
~watery discharge
~Congestion
~Sneezing
Little/No fever

Lab Diagnosis
· Virus culture
· Nasal washings
· EIA
· PCR

Epidemiology
· All throughout the year

Prevention
· No vaccine
· Wash hands
· Don’t touch eyes or nose
· Sneeze into tissue and throw away
· If possible, avoid person with cold or stay at home if you are the one with the cold

Orthomyxoviridae
Virus
· Influenza virus A
· Influenza virus B

structure of influenza virion

Morphology
· Typically spherical (100nm diameter)
· Enveloped
· Pleomorphic (many forms)
· Spikes on envelope
· Groups of HA (hemagglutinin) or NA (neuraminidase)
· Ratio of HA to NA—5:1

Genome
· ss (-) RNA in 8 segments
· 3 polymerase polypeptides with each segment
· 5’ and 3’ end of all segments highly conserved

Pathogenesis
· Respiratory tract in human
~Affinity of HA for receptors in the epithelium of the tract
· Innate resistance
~Mucus blanket/cilia
· Immunocompromised
~Elderly
~Premmies

Clinical Features
· High fever

· Prominent headache
· Aches/pains
· Fatigue

Lab Diagnosis
· Throat- swab/gargle/nasal wash
· Virus culture (MDCK cell line or chick embryo)
· Direct EIA (HA)
· PCR

Epidemiology
· All throughout the year
· Incubation (1-4 days)
· A few serotypes circulating
· Virus abundant in nasal discharge Antigenic Drift/ Shift

Antigenic Drift/ Shift
· Antigenic Drift
~Minor change in genome
~Both in A and B
~Point mutation
~Result in new strain
~happens all the time
· Antigenic Shift
~Major change in genome
~Only in A
~Gene reassortment
~Result in new subtype
~Happen occassionally

Strain Naming Convention
Type, animal species, place of isolation, number of isolate, year of first isolation, (H and N subtypes)

Control
· Vaccine for influenza (rendered useless by Antigenic Drift/ Shift)
· Antiviral drugs
~Receptor analog (prevent attachment)
~Transcriptase inhibitors
~Protease inhibitors (post-translational cleavage)
~Assembly of virions

Virus

Knowledges

**~~Viruses!!~~**
• Not made of cells.
• Cannot reproduce on their own.
• Do not grow or undergo division
• Do not transform energy.
• Lack machinery for protein synthesis.
• Are so small that they can only be seen with an electron microscope.

What are viruses made of?
• Viruses are composed of nucleic acid, proteins, in some cases, lipids as well. Nucleic acid which can be either DNA or RNA encodes the genetic information that is necessary to make copies of the virus.
• The nucleic acid is surrounded by a protective protein coat called a capsid. Some viruses are also surrounded by an outer membranous called an envelope, made of lipid and protein.

Structure of viruses?

Viruses display a wide diversity of shapes and sizes, called morphologies. Viruses are about 100 times smaller than bacteria. Most viruses which have been studied have a diameter between 10 and 300 nanometres.Most viruses are too small to be seen under a light microscope so scanning and tramission electron microscope are used to visulualise virus particle.

1) Helical structure

Structure of tobacco mosaic virus: the viral RNA is coiled inside the helix formed by repeating protein sub-units

2) Icosahedral structure

Electron micrograph of icosahedral viruses(Adenovirus)

3) Enveloped structure

Viruses are dependent on the envelope for their infectivity.

4) Complex structure

Structure of a typical bacteriophage

Shape of viruses?
There are predominantly two kinds of shapes found amongst viruses: rods, or filaments, and spheres. The rod shape is due to the linear array of the nucleic acid and the protein subunits making up the capsid. The sphere shape is actually a 20-sided polygon.

Genetic Change

How antigenic shift, or reassortment, can result in novel and highly pathogenic strains of human influenza

Viral Replication

DNA Viruses
The genome replication of most DNA viruses takes place in the cell's nucleus. If the cell has the appropriate receptor on its surface, these viruses enter the cell by fusion with the cell membrane or by endocytosis. Most DNA viruses are entirely dependent on the host cell's DNA and RNA synthesising machinery, and RNA processing machinery. The viral genome must cross the cell's nuclear membrane to access this machinery.

RNA Viruses
RNA viruses are unique because their genetic information is encoded in RNA. Replication usually takes place in the cytoplasm. RNA viruses can be classified into about four groups depending on their modes of replication. The polarity (whether or not it can be used directly to make proteins) of the RNA largely determines the replicative mechanism, and whether the genetic material is single-stranded or double-stranded. RNA viruses use their own RNA replicase enzymes to create copies of their genomes.

Reverse transcribing Viruses
Reverse transcribing viruses replicate using reverse transcription, which form DNA from an RNA template. Reverse transcribing viruses containing RNA genomes use a DNA intermediate to replicate, whereas those containing DNA genomes use an RNA intermediate during genome replication.