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

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Members

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

NYP SCL MB0804

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● @ Tuesday, October 28, 2008 ●

Lecture 3!

Hepadnaviridae

Family:
-Human Hepatitis B Virus
-Duck Hepatitis B virus
-Ground Squirrel Hepatitis Virus
-Snow Goose Virus
-Woodchuck Hepatitis Virus
-Wooley monkey virus

Unique Features:
-Non-segmented
-Single molecule of open circular, partially double-stranded DNA containing extensively overlapping genes

Morphology:

-Virions consists of an envelope and nucleocapsid.
-Capsid enveloped by sensitive lipoprotein.
-Envelope has no surface projections.
-Nucleocapsid is round, isometric and has icosahedral symmetry.
-Capsid surface structure reveals concentric rings.
-Capsid consists of 180 capsomers.

Pathogenesis:
-Acute or chronic liver infection depending on age.
-Only about 5% to 10% of Immuno-competent adults infected with HBV develop chronic hepatitis B

Clinical Features(Acute):
-Loss of appetite, nausea, vomiting, fever, abdominal pain and jaundice(skin and white part of eyes turn yellow).
-90-95% of acutely infected adults recover but 5-10% become chronically infected.

(Chronic):
-Potentially infectious patients have no symptoms upon laboratory testing.
-Others will have clinically apparent chronic hepatitis.
-Some goes on to develop cirrhosis.
-Hepatocellular carcinoma(primary liver cancer).

Lab Dignosis:
-Detectable HBsAG in acute infection
-IgM antibodies against core antigen are detectable in serum.
-IgG antibodies against core are produce.
-After acute infection resolves, IgG antibodies againt core antigent persist and IgM antibodies and HBsAg become undetectable.
-Most people that had resolved acute infection, continues to have IgG antibodies againt core antigen for life.
-Acutely infected Individuals whom do not clear HBV will continue to have serum HBsAG and diagnosis of hepatitis B is confirmed, prognosis is assessed, by liver biopsy.

Control:
-Post 1987 babies all vaccinated against HBV.
-Avoid risky sexual behaviour.

Herpesviridae

Alphaherpes: Herpes Simplex 1 virus, Herpes Simplex 2 virus, Varicella Zooster virus
Betaherpes: Cytomegalovirus, Human Herpes Type 6, Human Herpes Type 7
Gemmaherpes: Epstein Barr virus, Human Herpes Type 8

Unique features:
-Virus remain latent until reactivation(stress, Long exposure to sunlight, during menstrual period).
-Virus hide in nerves tissue. May cause brain damage to child if passed from mother to baby during birth.

Genome:
-Concentric Virion
-Linear ds DNA
-Three origin of replication

Herpes simplex viruses
Pathogenesis:
-HSV1(cold sores)
-HSV2(genital herpes)

Clinical features:
Herpes Simplex
-Cold sores: Blisters around mouth for 1 week. Affect eyes and gum.
-Genital herpes: Blisters, burning sensation, discharge for 1- 3 weeks.

Control:
-Do not kiss or have sexual contact

Varicella zoster virus
Pathogenesis:
-Respiratory tract, pharynx
-Herpes zoster(shingles)

Clinical features:
-Fever
-Lesion all over body
-Scarring
-May affect nervous system(Guillain Baiire syndrome)

Control:
-Vaccine available
-Avoid infected people

Cytomegalovirus
Pathogenesis:
-Virus in urine, saliva, semen, cervical secretion and breast milk

Clinical Features:
-prolonged high fever, chills, severe tiredness, a generally ill feeling, headache, and an enlarged spleen.
-lung problems, poor weight gain, swollen glands, rash, liver problems, and blood problems.

Control:
-Practice good personal hygiene
- Avoid mouth contact with the body fluids of young children.

Human Herpes type 6
Pathogenesis:
-production of a functional chemokine and chemokine receptors
-depletion of CD4 T lymphocytes via direct infection of intra-thymic progenitors and by apoptosis induction
-widespread in infants between 6 months and 2 years of age

Clinical features:
-minority of infants develop roseola infantum
-undifferentiated febrile illness is more common

Epstein Barr virus
Pathogenesis
-Nasopharynx, salivary gland

Clinical features:
-Fever
-Lesion all over body
-Scarring
-May affect nervous system(Guillain Barre syndrome)

Control:
-Do not kiss and stop sexual activity

Lab Diagnosis:
-Virus culture
-Antigen Test: EIA
-Blood test

References:
http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/00.030.htm
http://www.dhpe.org/infect/cytomegalo.html
http://www.virology.net/Big_Virology/EM/herpes_thumb.gif
http://images.google.com.sg/imgres?imgurl=http://stdgen.northwestern.edu/stdgen/bacteria/hhv2/herpes.diagram.jpg&imgrefurl=http://stdgen.northwestern.edu/stdgen/bacteria/hhv2/herpes.html&usg=__tJlP74zN2myNOpGTBzOvCD8ASYc=&h=228&w=221&sz=23&hl=en&start=2&tbnid=cf11IGpTQNsvVM:&tbnh=108&tbnw=105&prev=/images%3Fq%3Dherpesviridae%26gbv%3D2%26hl%3Den%26sa%3DG

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.