Brain Abscess Syndrome
Other Names: Cranial Abscessation Syndrome, BAS
Brain abscess syndrome is a disease described primarily in white-tailed deer in which abscesses (enclosed collections of pus) form within the brain. Several species of bacteria can be responsible for these abscesses, but the most common cause is Arcanobacterium pyogenes (formerly Actinomyces pyogenes and Corynebacterium pyogenes).
Brain abscess syndrome occurs sporadically in North American white-tailed deer, particularly bucks, and results in occasional deaths. This disease occurs naturally and infrequently, so it does not seem to significantly impact the deer or elk populations.
While A. pyogenes can cause abscesses to form in many animal species, particularly ungulates (hooved mammals), brain abscesses due to this bacteria are more common in deer. The bacteria also commonly cause abscesses in other parts of the body in deer, moose, pronghorn, and wild sheep. Brain abscess syndrome is best known in white-tailed deer.
Brain abscess syndrome probably occurs throughout North America in most of the white -tailed deer population range. These abscesses have been observed in white-tailed deer in Florida, Georgia, Idaho, Kentucky, Michigan, Minnesota, Missouri, North Carolina, New Jersey, New York, Pennsylvania, South Carolina, Texas, Virginia, Washington, Wisconsin, West Virginia, and Wyoming in the United States. This disease has also been observed in white-tailed deer in Alberta, British Columbia, Ontario, and Saskatchewan in Canada. Some studies suggest that brain abscesses may be less common in arid regions.
A. pyogenes is a bacterium that commonly lives on the skin and gums of deer, and causes infection when it enters wounds. This bacteria is also present in the circulation of all ruminants. Brain abscess often form when the bacteria enter wounds in the velvet of a buck's antler, a broken antler, or the pedicle (base of the antler) of a recently shed or damaged antler. After the bacteria enter an antler wound, they can damage the bone of the skull and enter the brain where the abscess forms. Most cases of brain abscess syndrome occur in adult antlered males in October through April. This is because open wounds associated with antlers often occur as a result of normal buck breeding behavior such as antler rubbing, sparring, and shedding. Females and immature males can also develop brain abscesses, though it is less common.
Deer with brain abscess syndrome may exhibit loss of coordination, apparent blindness, lack of fear, aggression, weakness, depression, and emaciation. Swollen eyes, broken antlers, swollen joints, and lameness may also be observed. Pus may be present in the eye sockets and pedicles.
Abscesses can be observed in the brain at necropsy. The bacteria must be isolated and identified in the laboratory in order to determine the species responsible for abscess formation.
Brain abscesses only occur sporadically in wild deer, and the disease is well advanced when the external signs are noted, so treatment is usually not attempted.
The bacteria responsible for brain abscess formation occur naturally on the skin of deer, and infection occurs as a result of natural breeding behavior, or trauma of other origin, so prevention and control is not feasible. If a hunter harvests a deer with pus in the eye sockets or pedicles, it likely has brain abscess syndrome. Cervids with BAS are not safe for human consumption because of the possibility of whole body dissemination of the bacteria (septicemia).
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