Aujeszky’s disease, also known as pseudorabies, is caused by Suid herpesvirus 1 (SHV-1), a member of the subfamily Alphaherpesvirinae and the family Herpesviridae. The virus infects the central nervous system and other organs, such as the respiratory tract, of a variety of mammals (such as dogs, cats, cattle, sheep, rabbits, foxes, minks, etc.) except humans and the tailless apes. It is associated primarily with pigs, the natural host, which remain latently infected following clinical recovery (except piglets under 2 weeks of age, which die from encephalitis). The pig is the only species able to survive a productive infection and therefore, serves as the reservoir host. Young piglets are highly susceptible with mortality rates reaching 100% during the first 2 weeks of life. These animals show signs of hyperthermia and severe neurological disorders: trembling, incoordination, ataxia, nystagmus to opisthotonos and severe epileptiform-like seizures. When pigs are older than 2 months, the respiratory forms become predominant with hyperthermia, anorexia, and mild to severe respiratory signs: rhinitis with sneezing and nasal discharge that may progress to pneumonia. Sows and boars primarily develop respiratory signs, but in pregnant sows, the virus can cross the placenta, infect and kill the fetuses, inducing abortion, return to oestrus, or stillborn fetuses. In the other susceptible species, the disease is fatal, the predominant sign being intense pruritus causing the animal to gnaw or scratch part of the body, usually head or hind quarters, until great tissue destruction is caused. Focal necrotic and encephalomyelitis lesions occur in the cerebrum, cerebellum, adrenals and other viscera such as lungs, liver or spleen. In fetuses or very young piglets, white spots on liver are highly suggestive of their infection by the virus. Intranuclear lesions are frequently found in several tissues. Vaccines should prevent or at least limit the excretion of virus from the infected pigs. Recombinant DNA-derived gene-deleted or naturally deleted live Aujeszky’s disease virus vaccines lack a specific glycoprotein (gG, gE, or gC), which enables the use of companion diagnostic tests to differentiate vaccinal antibodies from those resulting from natural infection.