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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● @ Tuesday, December 16, 2008 ●

Lecture 5!
Flaviviridae..

1) Properties
= Spherical enveloped virion, 40-50nm

= Inner core protein C

= Membrane / matrix protein M

= Envelope with glycoprotein peplomers (E)

= Single linear 11kb positive sense ssRNA and infectious mRNA

= 3' polyadenylated tail and 5' cap

= Cytoplasmic replication (perinuclear)

= Polyprotein from genomic RNA cleave

= 3 structural proteins
- core nucleocapsid protein C
- envelope glycoproteins M and E

= Several non-structural proteins

= Usually transmitted from a bite by the infected arthropod (mosquito or tick)

= Genomes consist of one piece of linear, single-stranded, positive sense RNA. And because the RNA is positive, the nucleic acid itself is capable of instigating an infection in the appropriate host cells. Total genome can range from 10 to 11 kilobase pairs.

2) Dengue
= most important arbovirus presently (from Southeast Asia to Americas to Pacific to Africa)
= 4 distinct serotypes based on neutralisation test: DEN-1, DEN-2, DEN-3, DEN-4; where DEN-2 shows greatest antigenic and genotypic distance from the others
= protective immunity after infection homotypic
= many infections asymptomatic
= acute infection resulting in: fever, severe headache (frontal), retro-orbital pain, nausea and vomiting
= severe muscle and bone pain
= severe arthralgia (joint sweling - mainly back) --> break bone fever
= maculopapular rash before recovery

= Dengue Haemorrahgic Fever (DHF)/Dengue Shock Syndrome (DSS)
- prior infection and age key factors (15 years and below) in DHF and DSS
- similar to yellow fever in biphasic nature:

initial symptoms similar to DF followed by remission
sudden deterioration of patient condition

- Symptoms include :

severe prostration
hypotension
circulatory collapse
bleeding and shock

- Bleeding

Petechiae in skin, mucous membranes (mouth)
Injection and punction sites
Gastrointestinal
Haemorrhagic pneumonia

= WHO Grading of DHF

- Grade 1: Fever with non-specific, constitutional symptoms and the only haemorrhagic manifestations being a positive tourniquet test
- Grade 2: As for Grade 1, but with specific haemorrhagic manifestations
- Grade 3: Signs of circulatory failure or hypotension
- Grade 4: Profound shock with pulse and blood pressure undetectable

= Pathogenesis
- Not well understood but still having 2 theories
1. Virulent strain theory
- some strains more virulent than others
- molecular studies show variations in sequences amongst different strains within serotypes
-early evidence pointed to DEN-2

2. Antibody enhancement
- Main theory for DHF / DSS
- Main cell target of DEN: monocytes / macrophages
- Most cases had prior infection or infants below 1 year had maternal Ab

= Possible causes of DSS / DHF
- Immune system overreacting
- Severe Acute Respiratory Syndrome

= Control means
- Insecticide
- Mosquitoes screen
- Remove stagnant water
- Quarantine

(Below: Dengue infection cycle)

3) Yellow fever
= Incubation period of 3 ~ 6 days
= Tropical disease in Latin America and Africa
= Viraemia, infectious, headache, malaise, nausea, lassitude, muscle ache (3 days)
= Flushing of head and neck, conjunctival injection, strawberry tongue

= Severe yellow fever
- Remission after acute yellow fever
- Haemorrhagic, hepatic and renal disease or failure, coffee-ground diathesis (black vomit), hypotension and shock
- Fever, vomiting, abdominal pain, dehydration, prostration
- Jaundice
- Bleeding from punction punction sites of injections and drip needles
- Massive haematemesis / haemoptysis / intra-abdominal bleeding
- Virus absent from blood, but antibody titre high, autoimmunity may play major role
- mortality of 20 ~ 50%
-survivors suffered from extended chronic jaundice before full recovery, but hepatic and renal failure may persist

= Control
- Attenuated vaccine

4) West Nile
= Mainly mild to no symptoms
= Fever, headche and body aches
= Skin rash and swollen lymph glands

= Severe symptoms include:
- Cross blood-brain barrier
- Encephalitis
- Meningitis

= Mainly in persons above 50 years
= West Nile Transmission

= Control
- insecticide
- no vaccine yet

5) References
http://www.ebi.ac.uk/interpro/IEntry?ac=IPR001122
http://carnot.utmb.edu/flavitrack/images/flavivirus_genome.png
http://www.cdc.gov/ncidod/dvbid/westnile/cycle.htm

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.