Which organisms can typically be classified as pathogens?

Pathogens are organisms that cause disease in their host. The most common and well-known pathogens are bacteria and viruses, which are responsible for a wide range of infections in humans, animals, and plants. Bacteria can invade host tissues, produce toxins, and disrupt normal biological functions, while viruses hijack host cells and replicate, often leading to cellular damage or death.

Although other groups like fungi and protozoa can also act as pathogens, the question specifically highlights bacteria and viruses, which are the primary focus of pathogenic classification in many educational contexts. Fungi can be pathogenic as well, especially certain molds and yeast, while protozoa represent a diverse group of single-celled organisms, some of which cause diseases such as malaria.

The classification of archaea is typically distinct from pathogens, as they are often extremophiles that do not usually interact with human hosts in a pathogenic manner. Thus, bacteria and viruses being the key representatives are valid in identifying organisms as pathogens.