Viral infections are caused by pathogenic viruses. They can range from mild to severe and can be treated with antiviral medications.

Innate immunity is the first line of defense against infection. It provides immediate protection against pathogens and is mediated by physical barriers, cells, and proteins. The innate immune system recognizes pathogens through pattern recognition receptors (PRRs) and responds by activating inflammatory responses.

Parasitic infections are caused by pathogenic parasites. They can range from mild to severe and can be treated with antiparasitic medications.