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Cytopathic Effect

What is Cytopathic Effect?

When a virus invades a host cell, its structure changes. This is known as the cytopathic effect. This condition occurs when the infecting cell causes the lysis of the host cell or when the cell dies due to its inability to reproduce. A virus causing morphological changes in the host cell is known as cytopathogenic.

The first sign of cytopathic effect or viral infection is the rounding of cells. The inclusion bodies are observed in the cytoplasm and nucleus of the host cell. These can be identified in the blood smear of the patients through light microscopy or electron microscopy. Some viral infections lead to the formation of syncytia. These are large cytoplasmic masses produced by the fusion of infected cells. It is composed of many nuclei.

Also read: Virus

Types of Cytopathic Effects

Total Destruction

This is the most severe type of cytopathic effect. This is seen with enteroviruses. This causes the death of all the cells in the monolayer.

This is observed by seeding the cells on a glass surface and a single layer of host cells is formed. The viral infection is introduced into the cells and the cells are observed. Within three days all the cells shrink and detach from the glass.

Subtotal Destruction

A monolayer of host cells is seeded on the glass surface and viral infection is introduced. Only a few cells detach from the glass surface after some time. This type of CPE is caused by togavirus, picornavirus, paramyxovirus, etc.

Focal Degeneration

In this, there is a direct transfer of the virus from one cell to the other. The host cells enlarged, rounded, and refractile. After some time, the cells detach from the surface. This type of cytopathic effect is exhibited by the herpes virus and pox virus.

Swelling and Clumping

This is a characteristic of adenovirus. The cells swell and become enlarged, clump together, and eventually detach from the surface.

Foamy Degeneration

A number of large cytoplasmic vacuoles are formed. It can be observed by fixing and staining the host cell. It is observed in retroviruses and flaviviruses.


This is also known as cell fusion. In this Cytopathic effect, the plasma membranes of the host cells fuse and form an enlarged cell. This cell contains at least four nuclei. This can be detected by fixing and staining the host cells. Herpes virus and paramyxovirus can be detected this way.

Inclusion Bodies

Insoluble abnormal structures in the nuclei or cytoplasm of the cells can only be detected through staining. inclusion bodies are areas of altered staining in cells. These inclusions may be large, small, single, multiple, intranuclear, intracytoplasmic, basophilic, or eosinophilic. Chromatin migration causes a thin stained ring around the edge of the nucleus.

Cytopathic Effect in Diagnostics

Cytopathic effects are used to diagnose viral infections. few cytopathic effects can be seen in unstained, unfixed cells under low power optical microscope. While a few cytopathic effects such as inclusion bodies can be seen in stained and fixed cells under a light microscope.

The cytopathic effects of a few viruses are specific and therefore can be used to diagnose viral infections in humans and animals. The rate at which a cytopathic effect appears is also used to diagnose the type of infections by the virologists.

Key Points Of Cytopathic Effect

  • The cytopathic effect refers to the changes in the structure of the host cell caused by viral infections.
  • The viral infection results in cell lysis.
  • The infection also reduces the ability of a cell to reproduce leading to cell death.
  • The cytopathic effects lead to the formation of inclusion bodies or syncytia that helps in diagnosing viral infections.

Also read: Viral Diseases

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