Abortive infection

Conditions of occurrence

Abortive interaction never concludes with the assembly of new virions. For the cycle to be interrupted, at least one of the three basic scenarios must occur:

1. Viral factor. A susceptible target cell is attacked by a defective agent — the so-called defective virus or defective virion.
2. Cellular factor. An absolutely normal, full-fledged (standard) virus enters the macroorganism, but it encounters a genetically resistant cell, i.e., one that is immune to it.
3. Environmental factor. A standard virus successfully penetrates a highly sensitive cell, but the external or internal environmental conditions turn out to be non-permissive. In such a situation, the process simply freezes at one of the stages.

Classification of defective agents

Not every viral particle is capable of initiating an infectious process independently. Microbiology distinguishes special groups of defective agents:

• Defective viruses. They act as independent species, but physically cannot replicate without outside help. They critically depend on the presence of a helper virus. Classic example: hepatitis D virus (delta agent) can replicate exclusively in the presence of hepatitis B virus.
• Defective virions. These are particles that, for various reasons, lack a portion of their genetic material. As a rule, they accumulate massively in the cell population under high multiplicity of infection (when cells are multiply infected).
• Defective interfering particles (DIPs). This is a special, specific group of defective virions whose main function is competition. They actively interfere with the standard virus, suppressing the production of full-fledged viral progeny.

Genetic cellular resistance

Cellular resistance is a powerful barrier against the generalization of infection. Protection mechanisms against infecting insensitive cells operate at different stages of interaction:

• Lack of receptors. Specific receptors are completely absent on the plasma membrane of the cell. The virus physically cannot attach and penetrate inside.
• Translation block. Even if the genetic material has penetrated inside, the cell blocks the process. It proves incapable of initiating viral protein synthesis on the viral mRNA template.
• Enzymatic deficiency. Specific tools are required for the assembly of viral macromolecules, primarily proteases and nucleases. If there is a deficiency of these in the cell, the synthesis of new particles becomes impossible.

Environmental factor impact

Sometimes the cell is fully susceptible and the virus is complete, but external factors make reproduction impossible. Such causes of infectious process interruption include:

• Changes in physiological parameters. An increase in the patient's body temperature (fever) or a pronounced pH shift. For example, changes in acidity are frequently observed in the focus of acute inflammation.
• Action of drugs. The direct effect of modern antiviral drugs also interrupts the cycle.

Important feature: an abortive infection is not always a final verdict for the virus. If conditions normalize and non-permissive factors are eliminated (e.g., temperature drops or pH levels stabilize), the process may well reactivate and transition into a productive type.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Mechanisms of genetic cellular resistance formation
• The role of proteases and nucleases in the synthesis of viral macromolecules
• Viral interference: mechanisms of cellular competition
• Transition of abortive infection to productive upon environmental change
• Features of parasitic virus reproduction using hepatitis D as an example

Other topics in the "Microbial Physiology" section

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