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اليوم حاط في بالي أبدأ الدراسة لامتحان الهيئة السعودية وعشان كذا بدأت بذي المخلوقات الصغار :sm188: :sm174: :sm188:
(الفيروسات )وما أدراك مالفيروسات ؛
حسبي الله عليك يالخسيسة ماخليتي حد من شرورك
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MEDICAL VIROLOGY
حسبي الله عليك يالخسيسة ماخليتي حد من شرورك
:sm175: :sm186: :sm195:
MEDICAL VIROLOGY
Virology: Science devolving with viruses
HISTORICAL BAKGROUND
- In 1892: I Winooski the first person who record the transmission of infection tobacco mosaic disease
- In 1898: Loeffter and frosch foot and mouth disease of cattle.
- In 1898: Beijerinch known virus which mean poison.
- In 1911: Tusort and Herelle discover Bacteriophage.
- In 1935: Stanely crystals of TMD.
- In 1940: After discover electron microscope start to known the type of viruses and his characteristics after that the culture of virus was know.
GENERAL PROPERTIES OF VIRUSES
Viruses are the smallest infections agent known. They cam infect man, animals, insect, plants and bacteria, The following properties distinguish viruses from other microorganisms:
- They are vary small in size.
- They contain one kind of nucleic acid (RNA or DNA) as their genome.
- They are ****bolically inert as they to not possess ribosome's or protein synthesizing apparatus.
- They are obligate intracellular parasites. Can only replicate inside living cells. Hence, they cannot be grown on artificial culture media.
The vary in size from 20-300 nm. Due to their small size.
- They can pass through bacterial filters
- They require high speeds (ultra centrifugation) for their sedimentation 10.000- 30.000 rpm (bacteria require 1000-3000rpm)
- They are only seen by the electron microscope (EM), except poxviruses. EM is the best method for measuring the size of viruses.
Each virus particle or virion is composed of a protein coat or capsid and nucleic core. The capsid with
Its enclosed nucleic acid is called nucleocapsid. Many viruses are naked but some viruses are enveloped.
Viral Capsid:
It is composed of small protein subunits called capsomers. The arrangement of the capsomers determines virus symmetry Function of the capsid are:
- it protects the viral genome (DNA or RNA) against in activation by nucleases.
- It is responsible for the structural symmetry of the virion icosahedral or helical.
- It participates in attachment of virions to zusceptiblecells.
- It determines the antigenicity of the virion, Antibodies formed against protein coat antigens neutralize virus infectivity.
Viruses contain either DNA or RNA but not both, Most DNA viruses are double stranded , while most RNA viruses are single stranded. The molecular weight and type of nucleic acid are specific for each virus group
Function of the nucleic acid :
- It is the infectious part of the virus, coreless particles are non infectious
- It carries the genetic information for:
- virulence or ability to parasitize cells.
- Antigenic specificity of the protein coat.
Viral Envelope:
Many viruses are surrounded by a lipid or lipoprotein envelope which may be covered with glycoprotein spike- like projections, which attach to host cell receptors during the entry of the virus into the cell duc to their lipid content such viruses are sensitive to ether.
Loss of lipids results in disruption of virus and loss of infectivity . the envelope may be partially or completely derived from host membranes during release from the cell by budding.
The surface proteins, whether the virus capsid proteins or the envelope by glycoproteins, are the principal antigens against which the host mounts it's some viruses produce proteins that act as super antigens.
VIRUS SYMMETRY:
Viruses have 3 types of symmetry:
1. cubical symmetry: These viruses resemble a crystal and are called icosahedral viruses.
2. Helical symmetry in which the particle is elongated The capsomers are arranged in aribbon which is wound in the from of helix or spiral around the spiral nucleic acid. Most helical viruses are enveloped e.g. influenza virus.
3. Complex symmetry in which the viruses are complicated in structure e.g. pox viruses which are brick shaped with ridges an the external surface. The bacteriophage is another example of complex symmetry.
Classification of viruses
Most clinically important viruses can be classified into groups according to their structural characters into:
RNA VIRUSES
· RNA Non- Enveloped viruses
- Picorna viruses
- Hepatovirus: HAV
- Rhinoviruses.
- Reoviruses: Rotacirus
- Caliciviruses: Norwalk virus, Hepatitis E virus
- Orthomyxoviruses: influenza virus,
- paramyxo viruses: RSV, Para influenza, measles, and mumps
- Rhabdoviruses: Rabies virus
- Retro viruses: HIV, HTLV
- Arbo viruses
- Flavi viruses: Encephalitis, yellow fever Dengue, west Nile viruses.
- Bunya viruses: Sandfly, Riftvalley fever viruses
- Filo viruses: Ebola virus
- Arena viruses: lassa fever virus
- Corona viruses and Astro viruses.
· DNA Non- Enveloped viruses
- Adeno viruses
- Papillomavirus
- parvo viruses: parvo B19
- Herpes viruses: HSV1,2, varicella Zoster, CMV, EB, HHV6,7,8
- Hepadna virus: Hepatitis B virus
- pox viruses: small pox, molluscumcontagiosum, monkey pox
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