Infection occurs when harmful microorganisms – viruses, bacteria, fungi, or parasites – invade the body and begin to multiply. Disease results when this invasion damages cells and tissues, leading to noticeable symptoms.
Here's a breakdown of how infection works:
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Entry: The infectious agent (pathogen) enters the body. Common entry points include:
- Skin: Through cuts, wounds, or insect bites.
- Respiratory system: Through inhaled droplets (coughing, sneezing).
- Digestive system: Through contaminated food or water.
- Urogenital tract: Through sexual contact.
- Mucous membranes: Through the eyes, nose, or mouth.
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Attachment: The pathogen attaches to specific cells or tissues in the body. This attachment is often facilitated by specific molecules on the surface of the pathogen that bind to receptors on the host cells.
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Multiplication: Once attached, the pathogen begins to multiply. Viruses replicate within host cells, while bacteria, fungi, and parasites can reproduce inside or outside of cells depending on the specific organism.
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Evasion of Host Defenses: The pathogen attempts to evade the body's immune system. This can involve:
- Hiding inside cells: Some pathogens can hide within cells, making it difficult for the immune system to detect and destroy them.
- Changing surface antigens: Some pathogens can alter the molecules on their surface (antigens) to avoid recognition by antibodies.
- Suppressing the immune system: Some pathogens release substances that suppress or weaken the immune system.
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Damage: As the pathogen multiplies and evades the immune system, it causes damage to the body. This damage can be caused by:
- Direct cell damage: Some pathogens directly destroy host cells.
- Toxins: Some pathogens release toxins that damage tissues.
- Inflammation: The immune system's response to the infection can cause inflammation, which can damage tissues.
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Transmission: The pathogen exits the body and spreads to a new host. This can occur through:
- Respiratory droplets: Coughing or sneezing.
- Fecal-oral route: Contaminated food or water.
- Direct contact: Touching an infected person or surface.
- Sexual contact.
- Vectors: Insects or animals that transmit the pathogen.
| Step | Description |
|---|---|
| Entry | Pathogens enter the body through various routes (skin, respiratory system, digestive system, etc.). |
| Attachment | Pathogens bind to specific cells or tissues using surface molecules. |
| Multiplication | Pathogens reproduce inside or outside of cells, depending on the organism. |
| Evasion | Pathogens employ various strategies to evade the host's immune system. |
| Damage | Pathogens cause damage to the body through direct cell destruction, toxin release, or triggering inflammation. |
| Transmission | Pathogens exit the body and spread to new hosts via respiratory droplets, fecal-oral route, direct contact, sexual contact, or vectors. |
Ultimately, infection occurs when pathogens successfully enter, multiply, and cause damage within the body, leading to disease. The body's immune system constantly works to prevent and fight off these infections.
