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The Daily Vet by petMD

The Daily Vet is a blog featuring veterinarians from all walks of life. Every week they will tackle entertaining, interesting, and sometimes difficult topics in the world of animal medicine – all in the hopes that their unique insights and personal experiences will help you to understand your pets.

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Recently, as I’m sure many of you are aware, the USDA confirmed a case of mad cow disease in a dairy cow in central California. This animal tested positive in a rendering facility, which is a plant where food animals of “lesser quality” are ground for things other than human consumption - like pet food, for example. This means, and the AVMA (American Veterinary Medical Association) has confirmed it, that no part of this animal with mad cow disease entered the human food chain. Whew.

But, whenever this weird disease rears its head in this country (which it has three other times — 2003, 2005 and 2006), I am reminded of how fascinating and terrifying this disease is. Let’s discuss about mad cow disease.

Firstly, the politically correct term for mad cow disease is bovine spongiform encephalopathy (BSE). Let’s try to be sensitive to all those cows out there that truly are mad, shall we? The name BSE describes perfectly what this disease does: causes a disease of the brain (encephalopathy), whereby it has the appearance of a sponge (spongiform).

Naturally, the next question is how the heck does a brain turn into a sponge? Here’s where we start to get creeped out. The infectious agent of BSE is a unique little thing called a prion (rhymes with ion). Prions are proteins — yes, mere proteins.

I cannot repeat this enough, not only because it blows my mind but because people just don’t seem to understand this: The cause of BSE is not a virus or bacteria or any other "live" and self-replicating agent.

Prions are proteins that are folded incorrectly. Let’s take one step back here for a second and meander on a side trip to biochemistry (I know, try not to get too excited). Proteins are large molecules made of a chain of amino acids. This chain folds into delicate shapes to form the final structure of the protein. Prions, for reasons yet unknown, are proteins that have folded incorrectly. Now, what’s the big deal about a stinking rogue protein not folding correctly, you ask? Well, it wouldn’t be a big deal except for the fact that any other protein that touches this prion then becomes incorrectly folded itself, thus "transmitting" this folding problem throughout the nervous system. Oh, and it just so happens that these incorrectly folded proteins cause holes in the tissue. Which is where the term spongiform comes in.

So, how does mad cow disease pass from cow to cow if it is in the brain? This requires a look at the "old way" of feeding animals. Animals that are raised for meat require lots of protein in their diet to build muscle — and build it fast. Cheap forms of protein come from the slaughter by-products of other animals, such as blood and bone meal. Well, when ground up bone meal containing bits and pieces of brain tissue were fed back to cattle, you’ve got a convenient way to pass along prions.

Most people remember, at least from a cursory perspective, the mad cow disease outbreak in the U.K. back in the 1980s and 1990s, where people were eating beef from animals that had this condition, which was then linked to a similar neurologic disease in humans, called variant Creutzfeldt-Jakob disease (vCJD). In 1997, the U.S. adopted a feed ban that prevented the feeding of cattle bone meal and other potentially BSE contaminated parts to other cattle. There is also a ban on the slaughter of "downer" cows — cows that can’t stand or walk.

I myself haven’t encountered any suspect cases of BSE, and unless there’s a horrible outbreak in the U.S., I don’t think I ever will for the following reasons:

1. BSE often takes a long time to develop clinical signs (i.e., mad cow disease symptoms).  Many cattle are slaughtered way before they are old enough to show signs. I rarely deal with cattle much over seven years of age. The oldest cow I’ve dealt with so far has been a 14-year-old Angus named Annie, and she’s really more of a pet.

2. Most neurologic bovine cases I see involve bacterial infections, thiamine or calcium deficiency, or (rarely) rabies. Although when you think about it, rabies is far easier to catch and much more prevalent than BSE. Maybe I just won’t think about that.

This little blog has actually only touched the surface about mad cow disease. I didn’t get to talk about how other species like mink, sheep, and even cats have their own types of transmissible spongiform encephalopathies. Perhaps another time? You bring the coffee and I’ll bring the donut holes (because we’re talking about holes in the brain — get it?).

Dr. Anna O’Brien

Image: NLshop & antoshkaforever / via Shutterstock

Comments  5

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  • Fascinating!
    05/18/2012 07:12am

    This is completely fascinating!

    Is there any evidence of "patient zero"? Guess that would have had to be many years ago. Did this begin as an abnormality in one bovine and then get passed along? Can the mutation be passed from mother to calf?

    Yes, I DID get excited on the side trip to biochemistry .

  • BSE
    05/18/2012 08:31am

    Kind of alarms me that rendered animals are in our pet's food. Wonder if they test all 4D animals for BSE. What else is going into the food we feed our furry friends?

  • 05/18/2012 05:09pm

    Hi Kayteenm's,

    I fully agree with you on how much we human's do not know what is really going into animal food. I am partial to dogs. I own a ShihTzu. Before I purchased him, I went on line to check on the best dog food out there, and here is what I found. Foster and Smith online. They are vet doctors. I also found the best is Wellness. Yes, it is more money, but my Sammy is well worth it. I read that "they" are grounding up dead animals, collars and tags for dog food!! I was so disgusted I am very cautious as to what I give Sammy.

  • mad cow
    05/21/2012 01:26pm

    The USDA is deceiving the public about the true risks from mad cow prion diseases.

    Out of about 35 million animals slaughtered, only 35,000 are tested for mad cow --1/10th of one percent. There are 1.9 million "Downers" - diseased, disabled, dead or dying cows each year. At least one million of the downers are rendered into pet and animal feeds. These downers are the animals most likely to have mad cow disease. But ONLY 5000 downers are BSE tested at the renderers - less than one quarter of one percent (0.0025%)

    http://www.aphis.usda.gov/animal_health/animal_diseases/bse/surv_in_usa.shtml


    Three out of four US mad cows had Bovine Amyloidotic Spongiform Encephalopathy (BASE). The USDA says this strain of mad cow disease presents no risk to humans or animals "because it is not transmissible".

    Published, peer reviewed studies reveal that BASE is highly virulent and easily transmissible to a wide host range (Lombardi, G. 2008)


    Dr. Claudio Soto, et al, have confirmed that Alzheimer's Disease (AD) is a transmissible prion disease - 6 million US victims - new case every 69 seconds.

    http://www.ibtimes.com/articles/336322/20120502/alzheimer-s-trigger-cause-mad-cow-prion.htm?utm_medium=twitter&utm_campaign=Alzheimers+Twitter+News&utm_source=twitterfeed

    The common neuropathy in AD victims, early onset AD, sporadic Creutzfeldt Jakob Disease, BASE mad cows and Chronic Wasting Disease deer is the presence of amyloid plaques in the brains.

    Alzheimer's Disease Trigger Mimics Mad Cow Infectious Agent
    http://www.ibtimes.com/articles/336322/20120502/alzheimer-s-trigger-cause-mad-cow-prion.htm?utm_medium=twitter&utm_campaign=Alzheimers+Twitter+News&utm_source=twitterfeed

    Potential source of prions in cows' diets: sewage sludge biosolids containing infective human and animal prions topdressed on grazing lands, hay fields, dairy pastures where livestock and wildlife ingest dirt and sludge with their fodder. http://www.alzheimers-prions.com/

    The pathway of risk from infected cows to humans:

    Aging asymptomatic dairy cows infected with BASE mad cow, are ending up UNTESTED in huge industrial mixing vats of hamburger, each containing meat from 50 to 100 animals from multiple states and two to four countries http://www.organicconsumers.org/madcow/burger21904.cfm





    Respectfully submitted, Helane Shields, Alton, NH hshields@tds.net

  • Patient Zero
    06/03/2012 08:13am

    For humans, it was a looooooooooong time ago!
    http://www.sciencedaily.com/releases/2003/04/030411071024.htm

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