Question

Discuss the general life cycle of viruses and relate key stages to their pathogenicity.

Answer 1

The life cycle of the virus

1) Attachment - in this the viral particle attaches themselves to its target cell.

2) Penetration - in this stage the viral particle by a process of endocytosis is engulfed into the epithelial cell.

3) Uncoating - Upon reaching inside the cell, the viral contents are released into the cytoplasm of the epithelial cell.

4) Biosynthesis - viral genome enters into the nucleus of the cell and itself got incorporated into the cell DNA, where the replication of viral genome results.

5) Assembly - replication of viral particles results in the formation of new phages.

6) Release to ECF - By a process of exocytosis, the made new phage particles are got released into the ECF, which go and affect new cells and results in more and more phages.

Pathogenesis of virus

1. The virus get implanted at its portal of the entry itself that is if it enters through nostrils it may implant itself in the respiratory tract itself.

2. Local replication - Some of the viruses are intracellular and release a number of viruses, thus spreads locally. Some viruses are capable to replicate inside the macrophage and other phagocytes.

3. Dissemination from the portal of entry - Virus which was local at one place spread to the other region via circulation that is carried by blood or lymphatics.

4. Incubation period - During this time viruses may have entered through portals and have multiplied locally and spreads. Still, then it is inert.

5. Multiply in target organ - Virus enters the body may be specific to some sites like it may be specific to respiratory or digestive or any other. And thus get multiply in that region.

6. Shedding of the virus - Virus infects some host cell and take its machinery to shed new daughter viruses.

7. Congenital Infections - Some viruses can pass through placental barrier and can cause infection to foetus also some can be transmitted through mammary secretion to the foetus.