Parasites that cause harm to their host are typically referred to as what?

Parasites that cause harm to their host are referred to as pathogens because they actively disrupt the normal functions of the host's body and can lead to disease or adverse effects. Pathogens can include various organisms like bacteria, viruses, fungi, and parasites that invade a host and elicit an immune response, ultimately leading to illness. This term emphasizes the harmful nature of the organisms involved, as opposed to other classifications like commensals, which typically live in harmony with their hosts without causing damage.

While the term "infectious agents" might describe something that can cause infections, it is a broader category that doesn't necessarily focus on the harmful impact, making it less precise in this context. Hostile organisms is not a standard biological term used to describe harmful parasites, and thus it lacks the specificity needed to accurately reflect the nature of these organisms. Therefore, "pathogens" is the most accurate and widely accepted term for parasites that are harmful to their hosts.