Mad cow disease, or bovine spongiform encephalopathy (BSE), only affects cattle and can only be accurately detected by microscopic examination of brain tissue after the animal’s death.

Consumption of BSE-contaminated meat and meat byproducts has been linked to variant Creutzfeldt-Jakob disease (vCJD) in humans. Like other transmissible spongiform encephalopathies (TSE), vCJD is difficult to positively diagnose.

When vCJD is suspected, treatable forms of dementia (e.g., encephalitis, chronic meningitis) must first be ruled out. This may involve a spinal tap or computerized tomography (CAT scan) of the brain. After other forms of dementia have been ruled out, a probable diagnosis of vCJD (or another TSE) can be made by a physician’s evaluation of the patient’s medical history (including whether any potentially contaminated beef products were consumed), the presentation of signs and symptoms, magnetic resonance imaging (MRI) of the brain and an electroencephalogram (EEG). In patients with vCJD, an EEG or brain MRI may reveal unique abnormalities.

vCJD can be positively diagnosed using a brain biopsy. This is an invasive and risky procedure that removes a small amount of brain tissue for laboratory examination. However, if the tissue is taken from a part of the brain that is not affected by the disease, it may produce a false negative result. The disease can be positively diagnosed with the greatest degree of reliability through a microscopic examination of brain tissue during an autopsy. However, this is only possible after death.

Research on new diagnostic tests for TSEs, including vCJD is ongoing.