👉 Infection occurs when a pathogen, such as bacteria, viruses, fungi, or parasites, enters the body and begins to multiply or cause harm to host cells, tissues, or organs. This process typically involves three stages: adhesion, invasion, and replication. Pathogens first attach to specific receptors on host cells, often through surface proteins. They then either invade the cells directly or trigger the cells to engulf them. Once inside, the pathogens replicate, either by hijacking the host's cellular machinery or by using their own resources. This replication can lead to cell damage, inflammation, and the symptoms associated with infection. The immune system responds by mounting an attack to eliminate the invading pathogens, but if the infection is severe or the host's defenses are compromised, it can result in disease.
