The pathogen that isn't: Mad Cow disease

Microbiology is a field that never fails to surprise me, but there was one particular disease I read about this week, and it really takes the microbiological cake in my opinion. Bovine spongiform encephalopathy (BSE) ravaged European cattle herds from 1987 to around 1999, and many would argue the beef industry is still reeling from its effects - especially in the UK, where beef exports were banned until 2006. Europe was worst hit because of its climate of all things. The main protein substitute used in the diets of cattle worldwide is soy bean, but in Europe the colder climate means they cannot be grown. So instead the ground up, heat treated remains of animals that died of disease or that were unable to enter the human food chain for some other reason, were used to give protein to commercial cattle. But the carcasses were heat treated weren't they? That would kill most pathogens capable of spreading disease to cattle, but BSE wasn't most pathogens. BSE appears to be caused primarily by mis-folded proteins known as prions (a combination of the words protein and infection). That stands in stark contrast to everything we know about how diseases spread; through viruses, bacteria or other living pathogens, all of which contain nucleic acids in genetic material of some sort: DNA or RNA. Prions are just non-living proteins, which act as a template, causing all proteins in their vicinity to become mis-folded also, and a chain reaction begins. This new, misshapen protein structure makes them more stable, so they accumulate in infected tissue, causing tissue damage and apoptosis. The majority of proteins affected by prions are in the brain, so symptoms of a prion linked disease include neuronal loss and therefore brain damage (hence BSE's more common name: mad cow disease). At this point, it seems that the spongiform encephalopathies caused by prions are unstoppable, as conventional antibiotics or other vaccinations are ineffective on a non-living disease vector. In the UK the epidemic of BSE was dealt with by culling all animals suspected to be infected, and the carcasses had to be placed in an alkaline hydrolysis digester. This literally lifesaving technology consists of an insulated steam-jacketed stainless steel vessel which operates at up to 70 psi and 149 C into which sodium hydroxide and water is added, heated and continuously circulated. This process degrades proteins into salts of free amino acids and the temperature and alkali concentrations deactivate prions by destroying their peptide bonds. If they reach the human food chain, prions can cause the neurodegenerative disorder Creutzfeldt-Jakob Disease (CJD), which has a 100% 1 year case mortality rate. A whole population could be wiped out if the contaminated meat was widespread enough. Terrifying right? And this wasn't even my Halloween post...