What kind of pathogens are there?

Pathogens are typically classified into four main categories: bacteria, viruses, fungi, and parasites. Bacteria are single-celled organisms that can cause infections like strep throat. Viruses are smaller infectious agents that require a host cell to replicate, leading to diseases such as influenza. Fungi can cause infections like athlete's foot, while parasites, which include protozoa and worms, live on or in a host and can cause various illnesses.