JUST when it looked as if we had mad cow disease licked, a new threat may be lurking down on the farm – bovine amyloidic spongiform encephalopathy. First discovered in Italian cows in 2003, BASE has infected a monkey, suggesting that the disease may also be capable of spreading to humans.
Alarmingly, the disease took hold – and killed – the monkey faster than strains of classical BSE and variant Creutzfeldt-Jakob Disease (vCJD), the human version of mad cow disease, injected into other monkeys as part of the same experiment. What’s more, the symptoms and brain damage look very like a rare form of “sporadic” vCJD, called MM2, which has no known cause, raising the prospect that BASE may already infect people.
Emmanuel Comoy of the in Fontenay-aux-Roses, France, and his colleagues made the discovery after injecting brain material from an Italian cow with BASE into the monkey’s brain. After 26 months, it was dead (PLoS ONE, ).
Advertisement
The monkey’s symptoms were different from those of other monkeys injected with human vCJD or classical BSE, and from people and cows with these diseases, whose cerebellum and brain stem are damaged. Instead of becoming aggressive and losing their appetite and ability to move, both the cow and the monkey with BASE lost their memories and the ability to orientate. This fits with damage to the cortex. “It’s as if they’re lost,” says Comoy. Significantly, humans with MM2 have similar symptoms and patterns of brain damage.
“We have here an atypical cattle strain of BSE that’s clearly transmissible to primates, that’s more easily transmissible than classical BSE, and which causes a different disease,” says Comoy.
“We have a strain of BSE that’s more easily transmissible than classical BSE and which causes a different disease”
He is now trying to find out if MM2 and BASE are the same disease by injecting mice with material from people infected with MM2, BASE cows and the dead monkey. He is also exploring whether monkeys can catch BASE by eating infected brain from cows, just as people contracted vCJD by eating beef contaminated with brain material from BSE-infected cows. “We’re four years into the eating trial, and the animals remain healthy, but we can’t be complacent as monkeys take five years to succumb to infection with classical BSE,” says Comoy.
“It’s entirely possible that some diseases we think are spontaneous CJD are actually caused by BASE, but it’s by no means proven,” says Chris Higgins, chairman of the UK government’s .
Even if MM2 turns out be the human form of BASE, Higgins says, the “health implications are minimal”, because the disease is so rare in cows and infective material remains banned from consumption. But Comoy says that the discovery should temper any temptation to ever relax screening for BSE.
BSE and vCJD – Learn more in our comprehensive special report.
