Animal diseases encompass a wide range of infectious, parasitic, genetic, and metabolic conditions that affect domestic pets, livestock, wildlife, and other animals. These illnesses may be caused by bacteria, viruses, fungi, parasites, nutritional deficiencies, or environmental factors, and some—known as zoonotic diseases—can be transmitted between animals and humans. Common examples include respiratory infections, gastrointestinal disorders, skin conditions, and chronic diseases such as diabetes or arthritis in companion animals, as well as herd-related infections in livestock that impact food production and public health. Symptoms vary widely depending on the species and condition but may include changes in appetite, behavior, mobility, or physical appearance. Prevention and management rely on proper nutrition, vaccination, hygiene, regular veterinary care, and monitoring to detect illness early and reduce spread.