Classical or atypical prions | Research leads to categorization of prion-related livestock diseases
BANFF, Alta. — There are little pieces of research into prion biology that link to form a chain of knowledge about a family of fatal neurological diseases in mammals and humans.
Cattle may be infected with BSE, sheep and goats succumb to scrapie and the wild deer and elk population are vulnerable to chronic wasting disease.
On the human side, Creutzfeldt-Jakob disease and possibly Alz-heimer’s and Parkinson’s disease and other neurodegenerative infections are deadly conditions with a link to aberrant proteins.
The protein that prions are made of is referred to as PrP and it is found throughout the body, even in healthy people and animals.
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However, PrP found in infectious material has a different structure and is resistant to proteases, the enzymes that can normally break down proteins.
If scientists could figure out what causes these proteins to go rogue and accumulate, live tests and cures could be the next step.
Research has led to the categorization of different strains of scrapie and BSE. Each type behaves slightly differently in the brain and affects animals at varying ages, said Jan Langeveld of the Central Veterinary Institute at Wageningen University in the Netherlands.
“There are many phenotypic properties you can study with this disease,” he said at the Alberta Prion Research Institute conference in held earlier this year in Banff.
Scrapie strains include the classical form, Nor 98, CH1641, atypical scrapie and Italian scrapie. Each form displays a different pattern in the brain when tested.
Scrapie eradication is a world wide goal with surveillance and genetic controls.
Many countries launched a program more than a decade ago to detect susceptible lines of breeding sheep and goats.
Those susceptible types were not bred and the incidence of scrapie has been reduced.
Atypical scrapie does not appear to be contagious but like atypical forms of BSE, surveillance needs to continue.
To gain a better understanding of how the various types of BSE behave, cattle were infected in 2011 at a Canadian Food Inspection Agency laboratory at Lethbridge.
Cattle either received injections of BSE into their brains or were fed infected material of either classical BSE or the atypical types, H and L.
A few are still alive at 40 months and are showing no signs of disease while others started to show symptoms.
“The disease progresses differently. It is slow but very continuous in atypical forms,” said lead researcher Stefanie Czub.
“We notice a continuous change in their behaviour.”
For example, those with the L type show anxiety and salivation when they are in a chute. They fall to their knees, balk at light and do not want to be touched.
When the animals die and their brains are analyzed, the patterns are different. The classical form was first seen in England when cattle ate contaminated feed. The obex contains the greatest amount of disease while the atypical forms are seen elsewhere.
Czub said precautionary approaches to this disease still apply even though scientists say the classical form seems to be disappearing as more countries enforce bans against feeding animal protein back to ruminants.
The feed bans should not be re-laxed to guard against the atypical types ending up in the rendering process with the potential to trigger more disease.
