BSE elicits no immune or inflammatory reaction. Clinical signs include abnormally stilted gait, high stepping, heightened sensory perception, itching, anorexia, excessive licking, and death. Most cases have been reported in the Holstein-Fresian breed, although all cattle are susceptible to the disease. Onset of clinical symptoms has been observed in cattle as young as 1 year 10 months, and may be precipitated by stress, estrous or calving. The disease course varies from less than 2 weeks to 14 months usually resulting in death or humane destruction within 4 months.
Clinical signs worsen with time.
Confirmation of disease is only possible following post-mortem examination of brain tissue. The infectious agent, or prion, attacks the brain, killing cells. Gaps in brain tissue develop, giving the brain a characteristic sponge-like appearance under the microscope. Prions may exist in the body for many years before symptoms begin, but death may then result within a year. CJD usually attacks people over the age of 55.