Short description
Pathogens are microorganisms, viruses, toxins and ionizing radiation that can cause disease. They are pathogenic organisms and substances, respectively.

Detailed description

One distinguishes between obligate pathogenic and potentially pathogenic organisms. Obligate pathogenic organisms always cause disease. For potentially pathogenic organisms, on the other hand, this is only the case in immunocompromised hosts. They usually belong to the host’s normal flora.