The Lowdown on Mad Cow

There are several diseases which strike concern in the human population, particularly diseases that are obtained by eating contaminated food (such as Salmonella poisoning) or  that can cross species (such as the flu). They are feared because of their ability to affect a wide number of people. One such disease is Mad Cow (or as my favorite microbiology professor would say, bovine spongiform encephalopathy), a disease that is caused my malformed proteins called prions. This disease can cross species, and a prime example is humans consuming infected cow meat. (To read up on Mad Cow, refer to this link: Mad Cow Disease)

Prions are malformed versions of the protein PrP. They not only are themselves deformed, but encourage other PrP proteins to malform. The main location of this perturbation is in the brain, with symptoms being observed often when it is to late.  Vincent Béringue from the French National Institute for Agricultural Research is challenging this view. His study has found that prions not only lurk in the brain, but are also found to hide in the lymphatic system (Prions enter stealth mode in the spleen, causing silent infections). In particular, the study has found that the spleen is a gateway organ for species transfer of prions. 

Species transfer mechanisms have been disputed, as species transfer is rare. It is rare because it is difficult for prions of one species to effectively convert PrP of another species. Béringue's study genetically engineered mice to express sheep prions, then exposed them to prions that cause chronic wasting disease in deer. The mice showed no or little symptoms of disease in the brain, but the spleen was found to have a very high prion content. Béringue also engineered the mice to express human prions and exposed them to the strain that causes bovine spongiform encephalopathy, as this would enable the study of animal to human transition. The results were the same as before, with the spleen containing a high amount of prions while the brain was relatively clean. Signs of disease was non existent, and only 10% of the mice had prions in the brain. 


This is a very interesting result, as Mad Cow disease could be diagnosed earlier than when symptoms manifest. Once the symptoms are present, often there is nothing that can be done to treat the patient. It shows that the spleen is the gateway organ, and hides within the body. What a "maddening" discovery!


~LD
Original Paper: Béringue, Herzog, Jaumain, Reine, Sibille, Le Dur, Vilotte & Laude. 2011. Facilitated Cross-Species Transmission of Prions in Extraneural Tissue. Science