Farming News - Sheep disease could infect humans
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Sheep disease could infect humans
Evidence has emerged that a deadly brain disease which affects sheep is similar enough to another feared zoonotic disease to potentially transmit to humans.
Variant CJD (Creuzfeldt Jakob Disease), the disease behind the BSE scare in the 1990s, is an example of a zoonosis: a disease which can spread between different species of animal. BSE – which affects cattle – is thought to cause variant CJD in humans, but the agent behind another form of CJD remains a mystery.
Scientists in France, looking at diseases caused by 'prions', misfolded proteins that replicate by transforming healthy proteins into misfolded ones, have suggested that the potential for scrapie prions to infect humans remains unknown.
Scrapie apparently causes chronic itching in infected sheep; it is named for the clinical signs displayed by animals suffering from the disease, who scrape their fleece against rocks and fences. The disease belongs to the same family as BSE and chronic wasting disease, which affects deer. Though Scrapie has been known since the early 1700s, there has never been any evidence that it could affect humans.
However, on Wednesday, scientists from the Veterinary School of Toulouse suggested there may be a link between scrapie and sCJD in humans. Though they said there is no proof that eating meat from animals with scrapie can cause disease in humans, they found evidence of a link between the infectious agent behind scrapie and human brain disease.
Writing in the journal Nature Communications, researchers concluded, "Our data on their own do not unequivocally establish a causative link between natural exposure to sheep scrapie and the subsequent appearance of sCJD in humans.
"However, our studies clearly point out the need to consider this possibility."
Tests on 'humanised' mice (which were genetically modified to express more human prions and have previously been used to confirm the zoonotic ability of BSE), showed that scrapie prions spread in the brain in the same way as sCJD prions.
The scientists said, "These results demonstrate that scrapie prions have a zoonotic potential and raise new questions about the possible link between animal and human prions."
Though the revelation that variant CJD is the human equivalent of cattle disease BSE, transferred to humans through certain meats, caused massive panic in the 1990s, there have only been a small number of recorded deaths from the disease.
Whilst it is the most common form of human CJD, sCJD is still very rare. The scientists pointed out that infection through indirect routes, such as eating contaminated meat could have an incubatio preiod lasting several decades. They said that, even if a causative link is established between sCJD and Scrapie, "It would be wrong to consider [sheep prions] as a new major threat for public health."
Their paper is available here