Agents cause disease through various mechanisms, including:
1. Invasion and Replication: Biological agents like viruses and bacteria invade the host's body and replicate, causing tissue damage and immune response. For instance, the HIV virus attacks the immune system, leading to AIDS.
2. Toxicity: Chemical agents can cause disease by producing toxins that damage cells and tissues. An example is lead poisoning, which affects multiple body systems, particularly the nervous system.
3. Physical Damage: Physical agents cause harm through direct physical interaction with the body. For example, prolonged exposure to loud noise can result in hearing loss.
4. Nutritional Imbalance: Nutritional agents lead to disease by disrupting the body's normal metabolic processes. For example, excessive intake of saturated fats can lead to cardiovascular diseases.
