LINDELL BEACH, B.C. – Eye exams have taken on a new dimension with the development of a test that detects a tell-tale glow in cattle eyes indicating BSE infection.
Researchers from Iowa State University’s chemistry department wrote in a recent issue ofAnalytical Chemistrythat central nervous system tissue forms pigments that glow when they are old or injured.
They found that the eye, and in particular the retina, has shown to be the most promising tissue to emit this unique glow.
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The ultimate goal of the study is to find a non-lethal, non-invasive method of testing a living animal with transmissible spongiform encephalopathies, which include BSE, but the first step has been to show the value of the eye as a diagnostic tool.
“What we look for are insults to the central nervous system so anything that would damage it would result in pigments in the retina,” said research team leader Jacob Petrich.
“The pigments that are produced show the presence of a neurological disease. They absorb light very strongly and they re-emit light in the form of fluorescence very strongly.”
The scientists used the eyes of sheep infected with scrapie, the most widespread TSE affecting sheep and goats worldwide.
It is characterized by poor condition, itching, imbalance, gait abnormalities, convulsions and death. It is incurable and requires quarantine, euthanasia and careful disposal of the carcass.
However, unlike BSE, scrapie is not considered infectious to humans.
A total of 140 eyeballs from 73 animals were obtained from a variety of sources. Thirty-five of the animals were scrapie-positive and 38 were scrapie-negative.
A fluorometer was used to examine various parts of the eyes at different wavelengths. The retinas showed large differences in spectral features when comparing scrapie-positive and scrapie-negative samples.
Petrich said the researchers weren’t looking for the prion proteins that are directly linked to TSE infections. Instead, they were looking for the neurological damage that prions can cause.
“The central nervous system doesn’t regenerate, unfortunately, and the aging or diseased material just accumulates,” he said.
“It is in our brains, in our spinal cords and in our eyes.”
His hypothesis is that animals going for slaughter would be young stock and, if healthy, would not have accumulated the pigment glow.
If the eyes did present a glow when examined, there would be cause for suspicion of a neurological disease.
He said it would most likely be a transmissible form such as BSE in cattle, scrapie in sheep or chronic wasting disease in deer and elk.
Petrich sees the potential for fluorescence imaging equipment in slaughter houses, where animals’ eyes could be tested immediately upon slaughter.
Testing live animals would be a desirable next step, but that requires animals to stand perfectly still while a retinal scanner is strapped to their head and a light shone in their eyes to record fluorescence.
“It’s hard enough to make humans sit still for these kinds of examinations,” Petrich joked, adding his wife can’t sit still for more than five seconds for an eye exam.
He hopes to develop a retinal scanner for use in slaughter houses and said that fluorescence spectroscopy is already used in slaughter houses to detect minute fecal contamination on meat.
He wrote that instruments developed for this application are used at beef processing plants in the United States and France.
