Microorganisms are tiny living creatures, such as bacteria, fungi, and viruses. Microorganisms are present everywhere. Despite their overwhelming abundance, relatively few of the hundreds of thousands of species of microorganisms invade, multiply, and cause illness in animals and people.
Types of Infectious Organisms
Type | Description | Examples |
|---|---|---|
Bacteria | Microscopic, single-celled organisms that have cell walls but lack internal structures | Escherichia coli, Salmonella species, and Staphylococcus species |
Fungi | Diverse, may be single-celled or multicellular organisms. Yeasts, molds, and mushrooms are types. | Aspergillus species,,Candida albicans, and dermatophytes (fungi that cause ringworm) |
Parasites | An organism, such as a worm or single-celled animal, that survives by living on or in another, usually much larger, organism (the host). | Dirofilaria immitis (heartworm), Ctenocephalides felis (a common flea), Sarcoptes (sarcoptic mite), Giardia, and Toxoplasma (single-celled organisms called protozoa) |
Viruses | Made up of genetic material that is contained in a protein coat. Viruses cannot reproduce on their own; a virus must invade a living cell and use that cell’s own mechanisms to reproduce. | Canine parvovirus, equine influenza viruses, and feline enteric coronavirus |
Many microorganisms live on the skin and in the mouth, upper airways, and intestines without causing disease. Whether a microorganism lives harmlessly in or on a pet, or invades and causes disease depends on both the nature of the microorganism and the state of the pet’s natural defenses.
This chapter provides a general introduction to the causes, signs, diagnosis, and treatment of infections.
