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MEDICAL MICROBIOLOGY (MMIC 201) Prepared by Nabeel Al-Mawajdeh RN,MSC. King Saud University-Aflaj College CHAPTER 3 Virology Nabeel Al-Mawajdeh RN.MCS Virology Virology means the studying of viruses.

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MEDICAL MICROBIOLOGY (MMIC 201)Prepared by Nabeel Al-Mawajdeh RN,MSC.King Saud University-Aflaj College

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CHAPTER 3Virology

Nabeel Al-Mawajdeh RN.MCS

virology
Virology
  • Virology means the studying of viruses.
  • Viruses are noncellular organisms. Viruses are unable to make their own proteins and essential enzymes. They depend on their host cell for energy and replication.
  • Outside of living cells, viruses are metabolically inactive. So viruses are obligate intracellular parasites and can only replicate in living cell.
  • The complete infectious virus particle is called virion and the genome is in a core enclosed by the capsid.

Nabeel Al-Mawajdeh RN.MCS

virology cont d
Virology (Cont’d)
  • No type of organism is safe from viral infections; viruses infect humans, animals, plants, fungi, protozoa, algae, and bacterial cells.
  • Some viruses – called oncogenic viruses or oncoviruses- cause specific types of cancer, including human cancers such as lymphomas, carcinomas, and certain types of leukemia.

Nabeel Al-Mawajdeh RN.MCS

viruses size and structure
Viruses Size and Structure
  • Viruses are too small in size. The majority of viruses measure between 10-300nm (.01-0.03µrn)
  • Most viruses are unable to be seen with a light microscope. Electronic microscopes are used to visualize virus particles.
  • All viruses consist of single or double stranded DNA or

RNA surrounded by protective protein coat called capsid. many viruses have additional structures such as envelope.

Nabeel Al-Mawajdeh RN.MCS

major components of viruses
Major Components of Viruses
  • Nucleic acid: the genome (set of genes) of virus maybe genes or RNA but not both of them.
  • Capsid: It is a protein shell, or coat, that encloses the nucleic acid genome.
  • Envelope: It is a lipid bilayer membrane surrounding the nucleocapsid of some viruses. The envelope carries glycoproteins, which f6iin projection or spikes. The virus that has envelope is called enveloped virus but the one who hasn't the envelope is called naked virus.

Nabeel Al-Mawajdeh RN.MCS

viruses shape
Viruses Shape
  • The capsid shape varies from:
  • Icosahedral. e.g. poliovirus, adenovirus, hepatitis A virus.
  • Helical. e.g. influenza virus, mumps virus, measles

virus.

  • Complex. e.g. poxvirus (the virus that causes smallpox in humans)

Nabeel Al-Mawajdeh RN.MCS

classification of viruses
Classification of Viruses
  • Viruses are classified in two ways:
  • According to nucleic acid type:

a. DNA viruses which have the DNA as a genome.

- Poxvirus. - Adenovirus.

- Pap virus. - Herpes virus.

b. RNA viruses which have the RNA as a genome.

- Myxovirus. - Toga virus.

- Corona virus. - Retrovirus.

- Reo virus. - Arbovirus.

Nabeel Al-Mawajdeh RN.MCS

classification of viruses cont d
Classification of Viruses (Cont’d)
  • According to disease they produce.

- Generalized disease. E.g. skin rashes in measles, rubella, chickenpox, yellow fever.

- Diseases primarily affecting specific organs.

Nabeel Al-Mawajdeh RN.MCS

virus replication
Virus Replication
  • Viral populations do not grow through cell division, because they are acellular. A virus is unable to grow or reproduce outside a host cell.

Nabeel Al-Mawajdeh RN.MCS

bacteriophage
Bacteriophage
  • Virulent bacteriophages always cause what is known as the lytic cycle, Which ends with the destruction (lysis) of the bacterial cell? The most phages, the whole process (from attachment to lysis) takes less than 1hour.
phases of virus replication
Phases of Virus Replication
  • Attachment (adsorption): the phage attaches to a protein or polysaccharide molecule (receptor) on the surface of the bacterial cell.
  • Penetration: the phage injects its DNA into the bacterial cell; the capsid remains on the outer surface of the cell.
  • Multiplication (biosynthesis): the phage genes are expressed, resulting in the production (biosynthesis) of viral pieces.
  • Assembly: the viral pieces are assembled to produce complete viral particles (virions)
  • Release: is when the host cell bursts open and all of the new virions escape from the bacterial cell.

Nabeel Al-Mawajdeh RN.MCS

viruses properties
Viruses Properties
  • Every virus contains only one type of nucleic acid- either DNA or RNA, unlike living cells, which have both?
  • Viruses must invade host cells to replicate.
  • Unlike cells, they do not divide by binary fission, mitosis, or meiosis.
  • They lack the genes and enzymes necessary for energy production.

Nabeel Al-Mawajdeh RN.MCS

viruses properties cont d
Viruses Properties (cont’d)
  • They depend on the ribosomes, enzymes, and metabolites of the host cell for protein and nucleic acid production.
  • Most viruses consist merely of nucleic acid surrounded by a protein coat (capsid).
  • Viruses can be seen only by electron microscopes and each virus have a fixed morphology (Helical, Polyhedral, Spherical, or complex)
  • Viruses can infect bacterial cells (bacteriophages)

Nabeel Al-Mawajdeh RN.MCS

virus cultivation
Virus Cultivation
  • Cultivation of viruses requires the use of living cells since viruses cannot grow on synthetic media.
  • The main systems for virus cultivation:
  • Tissue culture.
  • Chick embryo.
  • Laboratory animals.

Nabeel Al-Mawajdeh RN.MCS

routes of virus transmission
Routes of Virus Transmission
  • Oral transmission.
  • Direct skin contact.
  • Transplacental.
  • Droplet transmission.
  • Direct inoculation.
  • Sexual transmission.

Nabeel Al-Mawajdeh RN.MCS

common viral infections
Common Viral Infections
  • Enteroviruses: non-enveloped RNA viruses that cause a variety of diseases including paralytic poliomyelitis, pleurodynia, myocarditis, meningitis, and encephalitis.
  • Rhinoviruses: non-enveloped RNA viruses that cause the common cold.
  • Corona viruses: enveloped RNA viruses that frequently cause of the common cold.
  • Influenza viruses: enveloped RNA viruses that are a common cause of respiratory tract infection.

Nabeel Al-Mawajdeh RN.MCS

common viral infections cont d
Common Viral Infections (Cont’d)
  • Paramyxo viruses: enveloped RNA viruses that cause respiratory infections such as viral pneumonia and mumps.
  • Rubella viruses: enveloped RNA viruses that cause Rubella disease.
  • Herpes viruses: enveloped DNA viruses that cause several diseases. Some of these diseases are fatal like the encephalitis and cancer.

Nabeel Al-Mawajdeh RN.MCS

common viral infections cont d19
Common Viral Infections (Cont’d)
  • Rotaviruses: non-enveloped RNA viruses that cause acute infantile diarrheal disease.
  • Human retroviruses: which include human immunodeficiency virus (HIV). these viruses are single - standard RNA and have 2 type :- HIV -1 and HIV-2 .
common viral infections cont d20
Common Viral Infections (Cont’d)
  • The main risk groups for AIDS are:
  • Homosexuals and bisexuals males
  • Intravenous drug abusers.
  • Hemophiliac and blood transfusion recipients
  • The sexually promiscuous.
  • Children born to HIV-infected mothers.
  • Heterosexual contacts of HIV-infected individuals.

Nabeel Al-Mawajdeh RN.MCS

common viral infections cont d21
Common Viral Infections (Cont’d)
  • Hepatitis viruses: there are 5 types of these viruses (A,B,C,D,E) that cause the hepatitis; the most common one of them is HBV.

Hepatitis B virus:

HBV is enveloped DNA virus that causes hepatitis B. HBV is present in all body fluids of the infected person. The infection of HBV can be acute ( accompanied by fever, malaise, and followed by jaundice with enlarged and tender liver) and chronic.

A high effective and save vaccine against HBV is available.

Nabeel Al-Mawajdeh RN.MCS

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The End

Nabeel Al-Mawajdeh RN.MCS