Understanding Viroses and HIV

• Diseases produced by viruses are called viroses.
• Examples of viroses are given in the table below for different infected organisms.

Examples of viroses

• In humans: influenza, smallpox, chickenpox, poliomyelitis, mumps, viral hepatitis.
• In plants: tobacco mosaic, cucumber mosaic, potato leaf roll, onion virosis, corn mosaic, tulip virosis, peach leaf blister.
• In animals: swine fever, avian plague, foot and mouth disease, viral encephalitis in cattle ("mad cow disease").
• One very dangerous virosis in humans is AIDS, produced by the HIV (Human Immunodeficiency Virus).
• HIV attacks the immune (defense) system of the body.
• The disease is deadly, and is transmitted especially through unprotected sexual contact and blood transfusions.
• It is recommended to avoid unprotected sexual contact, and to use disposable syringes.

HIV Virus structure

• Has lipids, proteins, and nucleic acid (RNA).
• In the structure of this virus, there are two molecules of RNA in the center.
• The periphery has a lipo-protein bilayer membrane.
• In the case of viroses, as in other infections with pathogenic germs, the receptive organism defends itself by producing antibodies.
• Artificial immunization can be achieved through vaccination.

Interferon

• Animal and human cells, invaded by viruses, synthesize a substance (interferon) that blocks viral infection.
• Interferon is administered as treatment in some forms of cancer.
• Viruses are infectious entities, located at the boundary between living and non-living matter, therefore they do not have their own metabolism.
• Viruses multiply only in the host cell that they parasitize, and the dimensions of viruses are on the order of millimicrons (8-270 mµ).
• Viruses have various shapes: circular, cylindrical, spherical, etc.

Virus Classification

• According to several criteria:
  • Type of nucleic acid: adenoviruses (containing deoxyribonucleic acid - DNA) and riboviruses (containing ribonucleic acid - RNA).
  • Substrate (e.g., rabies virus attacks nerve cells).
  • Parasitized organism: plant, animal, human viruses.
• Viruses are made up of a protein envelope called capsomeres, and nucleic acids form the viral genome.

Virus forms

• Infectious mature virus (virion), which represents the morpho-functional unit of viruses.
• Vegetative virus, which is devoid of a capsid, multiplied in the host cell.
• Provirus, which is an integrated decapsidated virus into the host cell chromosome.
• Viruses can only multiply inside living cells.
• The virion enters the cell, becomes a vegetative virus and integrates into the host cell chromosome, transforming into provirus.
• The viral nucleic acid modifies the host cell biosynthesis.
• New virions, that will affect the host cell until its destruction emerge.
• Virions become free and infect new cells.

Lytic cycle stages of a bacteriophage:

• Attachment: the bacteriophage attaches to the surface of the bacterium.
• Inoculation: the bacteriophage injects its own DNA into the bacterial cell, and the capsid is eliminated.
• Multiplication: the bacteriophage DNA multiplies.
• Assembly: the bacteriophage components are assembled.
• Release: the bacterial cell is destroyed and releases bacteriophages that will infect other cells.