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

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♥Tang Xu Yun
♥Koh Jia Huan
♥Canice Tay

NYP SCL MB0804

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● LECTURE 15 (Please modify) @ Monday, February 2, 2009 ●

Lecture 15
Emerging Virus..

1) Definition
Emerging viruses are defined as known viruses that has newly appeared in a human population and is rapidly increasing in disease incidence.

2) Reasons for emergence
Virus Factors
= Spontaneous evolution of new virus entity (especially RNA viruses, which have short generation times and high mutation rates)
= Generation of novel strain due to co-infection of different strains in an individual (random assortment)

Human Factors
= Concentration of people with shared lifestyle
- similar habits, easy infection and spreading
= Breakdown of public health
- not likely in developed countries but more in developing countries (example, China, Africa.etc)
= Climate change
- rainfall might increase, therefore leading to more breeding of mosquitoes
- human population might not be able to adapt to climate change in time, therefore making them vulnerable to viruses
= Man invading natural habitat of animal
- deforestation for agricultural needs
- close proximity with wild animals and increases possibility of zoonoses

3) Spontaneous evolution of virus
= Viral population are heterogenous

= High mutation rates
- due to selection pressure

4) Random assortment
= H3N2 infects man, H5N1 infects birds
= H5 is efficient at attachment
= Co-infection of both

= Virus replicates within host
= RNA strands transcribed
= Viral protein synthesized
= A "new" virion was formed and released

5) Types possible

•H – Hemagglutinin
•N – Neuraminidase

•16 different H types
•9 different N types

•H1N1
•H3N2

Random Assortment: Avian Influenza in Humans
•Only four (4) strains of avian influenza virus are known to cause disease in humans: H5N1, H7N3, H7N7, and H9N2
•How many permutations are there actually?

Avian Influenza Virus
It comes from the family of Orthimyxoviridae, and enveloped genome RNA virus. Due to the rapid mutation of the RNA genome, it creates a new subtype/strain. It spreas rapidly and is difficult to control. In Avian Influenza virus, there are 4 strains which are known to cause disease in Humans.

They are: H5N1, H7N3, H7N7 and H9N2. H3N2 infects humans, whereas H5N1 infects birds. When these 2 come together, it causes co-infection of both, espeicallly since H5 is efficient at attachment, causing the virus to replicate inside the host. This causes the mutation of Avian Influenza. The RNA strands are transcribed and viral proteins are synthesized. Therefore, a new strain is formed (H5N2) and are released to infect other cells.

Reasons for Emergence Human Factors
- Concentration of people with shared lifestyle
- Breakdown in public health
- Climate change
- Man invading natural habitat of animal

Concentration of people with shared lifestyle and breakdown of public health, though it is unlikely to happen in developed countries. People with shared lifestyle tend to be closer to one another. Climate change and viral disease contributes to the cause of there emerging viruses. Man invading animal's natural habitat such as deforestation for agriculture needs. This causes us to be closer to wild animals and increases the possibility of zoonoses.

Man Invading Animal Natural Habitat
•Deforestation for agricultural needs
•Closer to wild animals
•Increase possibility of zoonoses

Emerging Viruses over NEXT 5 years
- ???

Emerging Viruses over last 6 years
Now - Influenza virus (Orthomyxovirus)
November 2002-july 2003 - SARS (Coronavirus)
september 1998-april1999 - Nipah virus (Paramyxovirus)

6) References
http://en.wikipedia.org/wiki/Viral_evolution

http://www.cdc.gov/flu/avian/gen-info/facts.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.