Veterinary Science also called VETERINARY MEDICINE, the prevention, diagnosis, and treatment of the diseases of domestic animals and the management of other animal disorders. The field also deals with those diseases that are intercommunicable between animals and humans. Persons serving as doctors to animals have existed since the earliest recorded times, and veterinary practice was already established as a specialty as early as 2000 BC in Babylonia and Egypt. The ancient Greeks had a class of physicians who were literally called "horse-doctors," and the Latin term for the specialty, veterinarius ("pertaining to beasts of burden") came to denote the field in general in modern times. After a period of virtual nonexistence during the Middle Ages, veterinary science revived in the mid-18th century, when the first veterinary schools in Europe were established. Veterinary science rapidly regained its lost status, and its subsequent development largely parallels that of modern medicine. The preventive and control measures used in veterinary science are of vital economic importance to the livestock industry. Such common animal diseases as mastitis, brucellosis, swine fever, erysipelas, anthrax, and leptospirosis can cause major losses among stock animals and must be controlled or prevented by veterinarians. Vaccination and immunization, sanitation measures, and the rigid segregation, or quarantine, of sick animals are important tools used to combat the spread of infectious diseases such as anthrax, bovine tuberculosis, brucellosis, canine distemper, and rabies. Veterinarians also treat parasitical infections, conditions resulting in impaired fertility (in livestock), and nutritional disorders, and they often set broken limbs and neuter domestic pets. A veterinarian's training must include the basic preclinical disciplines of anatomy, histology, physiology, pharmacology, microbiology (including bacteriology, virology, and parasitology), and pathology. The clinical subjects of study can be broadly divided into internal medicine, surgery, preventive medicine, and clinical practice. Internal medicine includes the diagnosis and treatment of diseases as they affect animals. Preventive medicine and public health concern the broader aspects of disease prevention and control, especially of those diseases transmissible between animals and humans or affecting human welfare. Surgery includes wound treatment, fracture repair, the excision of body parts, and the related techniques of radiology, anesthesiology, obstetrics, treatment of lameness, and so on. In most veterinary schools, a clinic is operated to enable students to observe and assist with actual cases of disease or other conditions requiring attention. In both medical and surgical treatment, the same techniques are used as in medical practice on humans. Many veterinarians specialize either in the care of small animals, i.e., pets, or in the care of livestock. A few veterinarians specialize in the care of wild animals held in zoos. In most countries of the world, professional veterinarians must complete an educational program of from four to six years of work at the university level, after which they must obtain a license to practice from some duly constituted authority. In many countries the degree of doctor of veterinary medicine (D.V.M.) is awarded after successful completion of such a formalized course of study. Veterinary associations exist in practically all countries, their purpose being to advance the standards and improve the services of the profession.