Final answer:
A. Pathogens
Pathogens are microorganisms that cause illness and spoil food, and include bacteria, viruses, parasites, and prions. They are harmful to both human health and agriculture, leading to considerable morbidity and spoiling crops through diseases and toxins.
Step-by-step explanation:
Microorganisms that can cause illness and are found in various environments like air, soil, plants, water, and some food are known as pathogens. These include bacteria, viruses, parasites, and prions. Pathogens are notorious for causing foodborne diseases such as norovirus, Salmonella species, Clostridium perfringens, and Campylobacter jejuni. Moreover, parasites like pork tapeworm and the prions responsible for mad-cow disease can cause significant harm when transmitted to humans through contaminated food. Pathogens are also a major contributor to water pollution, leading to waterborne diseases that affect nearly a billion people globally, causing deaths, particularly in underdeveloped countries. While pathogens are detrimental to human health, causing various infectious diseases, they also attack crops, leading to plant diseases and food spoilage. Fungi, for instance, are common plant pathogens that not only destroy plant tissue but also produce toxins that can lead to diseases like ergotism in animals and humans.