Microorganisms are tiny living things, like bacteria, fungi, parasites, and viruses. They're everywhere, but only a small number that live in or on animals and people cause disease.
Bacteria are microscopic organisms with cell walls and a simple structure. Examples: E coli, salmonella, staphylococcus (commonly called "staph")
Fungi include yeasts, molds, and mushrooms. Examples: aspergillus, candida, ringworm
Parasites are organisms that live on or in a host and may cause harm. Examples: heartworm, flea, sarcoptic mite, giardia, toxoplasma
Viruses are extremely tiny organisms with a protein coat protecting their genetic material. They can only reproduce by invading a host's cells. Examples: canine parvovirus, horse flu, feline coronavirus
Many microorganisms live on the skin of pets and in their mouth, airways, and intestines without causing any illness. Whether a microorganism is harmless or causes disease depends on its properties and on the strength of the pet’s defenses.
This chapter reviews causes, signs, diagnosis, and treatment of different types of infections.
