Pathogens

Fungi

Fungi are typically decomposing organisms and include yeasts, many molds, and mushrooms. Diseases that are caused by fungi pathogens include athlete's foot, Valley fever, ring worm, and human yeast infections.

Bacteria (Kingdom Monera)

Living organisms are divided into two different types of cell types, prokaryote cells and eukaryote cells. Prokaryote cells do not have an isolated nucleus, and are far more simple than eukaryote cells. Bacteria are single-celled organisms made up of prokaryote cells. Fungi, plants, and animals are composed of eukaryote cells. Diseases that are caused by bacterial pathogens include tetanus, pneumonia, typhoid fever, Lyme disease, cholera, leprosy, trichinoses, botulism, gonorrhea, and syphilis. Not all bacteria are pathogens. Bacteria are useful in nutrient cycles, treating wastes, decomposing dead organisms, living inside our bodies to help us digest food, and making yogurt and cheeses.

Protists

Protists range in size and function more than members of the other kingdoms. Protists can be plant-like, fungus-like, or animal-like. Students might be most familiar with ciliated, animal-like paramecium found in pond water. SCUBA divers may be familiar with plant-like protists, kelp. Slime molds are sometimes mistaken for fungi. Diseases that are caused by protist pathogens include malaria, giardiasis, African amebic dysentery, and sleeping sickness. Many molds produce strong allergens.

Plants

Very few plants are considered pathogens. However, at this point, the definition of pathogen may become subtle. For example, food poisoning is a disease that is caused by the toxic metabolic wastes of bacteria. When a plant produces a toxin, we simply call it a poison, not a disease. Plant toxins are very prevalent. Sometimes plants evolve the production of toxins as part of their protection; sometimes the fact that a plant is poisonous to humans is coincidental.

Viruses

Viruses are so simple that most scientists consider them an organized assembly of organic molecules rather than a living organism. Instead of having a cell, they hold DNA or RNA inside a protein shell. Instead of metabolizing nutrients on their own, viruses take over the cellular machinery of their host in order to reproduce. Every living kingdom plays host to some virus or another. Typical viral human pathogens cause diseases such as flu, Four-Corners disease, HIV, herpes, and Ebola hemorrhagic fever.

Animals

While most animals that are avoided because of their role in causing disease are done so because they are vectors, some families of Kingdom Animalia are pathogens. For example, worms are animals and cause diseases such as Guinea Worm disease.