Pathogens are microorganisms, such as viruses and bacteria, that can cause disease in living organisms. They invade the body and disrupt normal bodily functions, leading to illness.
Bacteria are single-celled microorganisms that can be found almost everywhere. While some bacteria are harmless or even beneficial, others can cause infections and diseases.
Parasites: Parasites are organisms that live on or inside another organism (the host) and rely on it for survival. They harm the host by taking nutrients or causing damage to tissues.