An auditory hallucination, or paracusia, is a form of hallucination that involves perceiving sounds without auditory stimulus. While experiencing an auditory hallucination, the affected person would hear a sound or sounds which did not come from the natural environment. A common form of auditory hallucination involves hearing one or more voices without a speaker present, known as an auditory verbal hallucination. This may be associated with psychotic disorders, most notably schizophrenia, and this phenomenon is often used to diagnose these conditions. However, individuals without any psychiatric disease whatsoever may hear voices, including those under the influence of mind-altering substances, such as cannabis, cocaine, amphetamines, and PCP. There are three main categories into which the hearing of talking voices often fall: a person hearing a voice speak ones thoughts, a person hearing one or more voices arguing, or a person hearing a voice narrating their own actions. These three categories do not account for all types of auditory hallucinations. Hallucinations of music also occur. In these, people more often hear snippets of songs that they know, or the music they hear may be original. They may occur in mentally sound people and with no known cause. Other types of auditory hallucinations include exploding head syndrome and musical ear syndrome. In the latter, people will hear music playing in their mind, usually songs they are familiar with. These hallucinations can be caused by: lesions on the brain stem (often resulting from a stroke), sleep disorders such as narcolepsy, tumors, encephalitis, or abscesses.
Occasionally the infection can be extensive and persistent if the animal does not produce an immune response. A live virus vaccine (ATCvet code: QI04AD01 (WHO)) is made from scab material and usually given to ewes at the age of two months, but only to lambs when there is an outbreak. The vaccine can cause disease in humans. In sheep and goats, the lesions mostly appear on or near the hairline and elsewhere on the lips and muzzle. In some cases the lesions appear on and in the nostrils, around the eyes, on the thigh, coronet, vulva, udder, and axilla. In rare cases, mostly involving young lambs, lesions are found on the tongue, gums, roof of the mouth and the oesophagus. It has also been reported a number of times to cause lesions in the rumen. In one case it was shown that a severe form of orf virus caused an outbreak involving the gastrointestinal tract, lungs, heart, as well as the buccal cavity, cheeks, tongue and lips. Another severe case was reported pharyngitis, genital lesions and infection of the hooves which led to lameness and, in some cases, sloughing of the hoof.More typically, sheep will become free of orf within a week or so as the disease runs its course. Sheep custodians can assist by ensuring infected lambs receive sufficient milk and separating out the infected stock to slow down cross-transmission to healthy animals. It is advisable for those handling infected animals to wear disposable gloves to prevent cross infection and self-infection.