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Brain abscesses or cranial abscessation syndrome (CAS)

Brain abscesses in deer (also called cranial abscessation syndrome or CAS) are infections within the brain that produce abscesses that contain pus. The infections are usually caused by the bacterium Trueperella pyogenes. These bacteria are commonly found on the skin and gums of deer. Any deer can become infected with these bacteria and develop a brain abscess, however, it is most commonly reported in male deer.


Infection occurs when bacteria enter a wound. It is most commonly seen in male deer when bacteria enter through a break in the velvet of a buck's antlers, through a broken antler or the pedicle (antler base) after antlers are shed. After entering through a wound, the bacteria can damage the bone of the skull sufficiently to penetrate and cause an abscess in the brain.


Adult antlered deer from all over Wisconsin have been diagnosed with cranial abscessation syndrome (CAS). Deer may appear blind, and uncoordinated and may show abnormal behavior such as aggression toward people and stationary objects, or not moving when approached by people or dogs. Signs of CAS include swollen eyes, broken antlers weeping fluid, swollen joints, foot sores and lameness. Pus may be observed at the base of the antlers or in eye sockets. This is more commonly reported in bucks than does, likely because the bacteria enter wounds that result from sparring between bucks.


Because the bacteria that cause CAS are naturally occurring in the environment and infection is generally due to trauma from natural deer behavior, management is not practical. It only affects individual deer and is not spread from deer to deer.


Harvested deer that have pus at the base of the antlers or in or around the eyes may have this bacterial infection. Though the meat may be contaminated with the CAS-causing bacteria, the infection is usually limited to the head. No part of the head should be eaten. Normal cooking temperatures will destroy the bacteria, however, if any other part of the deer appeared abnormal it is best not to consume the meat.