A pathogen is any organism or infectious agent that causes disease in a host. Common types of pathogens include viruses, bacteria, fungi, protozoa, parasites, and even infectious proteins called prions
. Pathogens differ from the normal microbes living in or on the body because they can cause illness when they enter the body or when the immune system is weakened. They survive by infecting a host, evading the host's immune defenses, and using the host's resources to replicate and spread to new hosts
. Here are the main types of pathogens:
- Viruses: Tiny agents that require living cells to reproduce, causing diseases like the flu and common cold
- Bacteria: Single-celled organisms that can multiply outside the host; some cause food poisoning or skin infections
- Fungi: Can be single- or multi-celled; cause infections like athlete’s foot and yeast infections
- Protozoa: Single-celled organisms that can be parasitic, causing diseases like malaria
- Parasites: Larger organisms such as worms and lice that live on or in hosts and cause harm
- Prions: Infectious proteins that cause rare but serious diseases like mad cow disease
In summary, a pathogen is any infectious agent capable of causing disease by invading a host and overcoming its immune defenses
