Cattle infected with mad cow disease give off a tell-tale glow in their eyes, according to new research published in the journal Analytical Chemistry. In future, the discovery could lead to a long-sought test to detect infection with the agent that causes mad cow disease, preventing it from spreading throughout the food supply for humans.
In addition to posing a threat to humans, mad cow disease has devastated cattle operations in the past. During an epidemic of the disease in the United Kingdom, for example, more than 179,000 cattle were found to be infected and 4.4 million cows were slaughtered. Scientists have been trying to better understand mad cow disease ever since.
People may contract a brain-wasting disease similar to bovine spongiform encephalopathy (BSE) and to scrapie if they eat contaminated meat. Just like BSE, the Creuzfeldt-Jakob disease (CJD) in humans is a type of transmissible spongiform encephalopathy (TSE).
Jacob Petrich in the Department of Chemistry at Iowa State University and colleagues conducted the new research. They note that the human form of mad cow disease is linked to eating beef from animals infected with abnormal proteins called prions implicated in a range of brain diseases.
Past studies suggest that chemical changes in an animal’s retina, the light sensitive nerve tissue in the back of the eye, may provide a basis for detecting prion diseases.
The characteristic fluorescent signatures are thought to be the result of an accumulation of lipofuscin in the retina, explained Petrich and his team.
Lipofuscin is pigmented waste material that's made up of free radical-damaged proteins and fats. In human skin it's the common cause of age spots.
The scientists determined that retinas of sheep infected with scrapie, which is similar to mad cow disease, emit a characteristic glow—likely due to the colour waste material— when examined with a beam of light from a special instrument. The researchers therefore believe that relatively simple, non-invasive eye tests based on this finding could lead to fast, inexpensive diagnosis of prion diseases and other neurological diseases.