Mad Cow Disease: Mad Men, Mad Cows

Aliases: mad cow disease bovine spongiform encephalopathy, BSE

Agriculture isn’t just cornfields; sometimes it’s what that corn gets fed to. In the West, we love meat and dairy, and that means we need cows. Lots of cows. In an effort to maximize production and minimize costs, while keeping the livestock healthy, humans have done some pretty wild things. One of mankind’s more eccentric ideas was to provide protein to cows in the form of meat-and-bone meal made from, among other things, cows. In the 1980s, this dubious practice led to the first recorded outbreak of bovine spongiform encephalopathy (BSE), better known as mad cow disease1.

BSE is a transmissible spongiform encephalopathy or prion disease that results in a neurological disorder in cattle. It likely originated with a different prion disease, scrapie, which afflicts sheep. In the UK sheep were also used in the meat-and-bone meal fed to cows, and it is believed that scrapie-infected feed transmitted the illness to their bovine brethren, where it evolved into mad cow disease. It was then spread through UK herds via contaminated meal. The first cases were detected in 1986 and the epidemic peaked in 1993, with almost 1,000 new cases per week.

There is a (very thin) silver lining to this story. BSE is transmitted exclusively through feed, not cow-to-cow, so once the cause of the outbreak was identified and preventative measures were put in place, the number of cases plummeted. In 1995 there were 14,562 cases in the UK, which dropped to 1,443 by 2000 and 11 in 2010. Now, back to the bad news: BSE took a serious toll. As of 2010, there have been 184,000 cases in the UK altogether (in more than 35,000 herds)1.

To add injury to injury, BSE may have given rise to another prion disease, this time in humans. Variant Creutzfeldt-Jakob disease (vCJD) was discovered in the UK in 1994, within the incubation period of the beginning of the BSE epidemic1. By the end of 1996, there had been 15 cases of vCJD2, with symptoms similar to BSE2. If BSE did cause vCJD, then humans are not entirely innocent in its emergence, but the punishment may exceed the crime. vCJD is a brutal disease; the median duration of illness is 13-14 months, and the median age of death is 281.

mad cow disease
You are what you eat.

Cause: The pathology of mad cow disease is not well understood, but the disease is thought to be caused by a misfolded protein, called a prion. There are 3 strains: typical (the strain that the caused the outbreak in the UK, and is linked with vCJD), and two atypical strains, H and L. The atypical strains are very rare, and are thought to arise spontaneously in cow populations, and not be transmitted1. Speaking of transmission, it appears that BSE, like some other prion diseases is not transmitted cow-to-cow, but through environmental exposure; in this case, eating contaminated meat-and-bone meal2.

Consequence: BSE damages the central nervous system of cattle1, causing lesions in brain that result in behavioral changes (fear or aggression), ataxia (uncoordinated gait, falling, tremors), and dysesthesia (abnormal response to touch and sound)2.

Cure: Because there is no cure for mad cow disease, the best protection against it is prevention: not feeding BSE-contaminated meal to livestock. Fortunately, legislation has been enacted to eliminate contaminated meal from the animal feed system. In the UK, no cow over 30 months of age can be used for human food or animal feed, and as of 2009, most proteins, including tissue potentially infected with BSE (opaquely referred to as “specified risk materials” or SRMs) have been banned from the entire animal feed system, including fertilizers and pet feeds, in the US and Canada. Aside from prevention strategies, herds are kept under surveillance, and sick animals are culled1.

References

  1. “BSE”. Centers for Disease Control and Prevention. 21 February 2013. Web. 16 November 2014. http://www.cdc.gov/ncidod/dvrd/bse/
  1. Nathanson, N, J Wilesmith, & C Griot. (1997). Bovine Spongiform Encephalopathy (BSE): causes and consequences of a common source epidemic. American Journal of Epidemiology, 145(11):959-969.

Image source: Creative Commons, https://www.flickr.com/photos/usdagov/13250283675/

Monoculture Madness

Everyone needs to eat. As the world’s population continues to increase, so does the demand for food. Although we currently produce more food than we need globally, it isn’t distributed evenly, leaving more than 800 million people hungry3. We have tried to combat this disparity by increasing crop yields through intensified agricultural efforts: bumping up the use of chemicals, both pesticides and fertilizers, and converting more land to crop fields and pastures. As of 2004, nearly 40% of the world’s land surface was used for the production of food1. Agriculture is now the most common way that humanity interacts with its environment.

Monoculture, the practice of planting of a single crop over a wide area and several consecutive years, is one component of agricultural intensification. It emerged in lockstep with the technological advancement of farm equipment. Using a tractor to plant and harvest cuts down on labor costs and increases the amount of land you can farm, and it becomes more efficient to grow crops separately, rather than mixing them within a field. But this approach comes at a high cost to the environment, human health, and the health of the animals and plants we depend on.

Biting the hand that feeds you

Monoculture farming has had a massive impact on the American landscape. More than two thirds of the USA’s 315 million acres of farmland are dedicated to producing just four crops: corn, soy, wheat and cotton2. Unfortunately this technique demands greater amounts of pesticides and fertilizers than polycultures (mixed crop fields), because it leaves crops more vulnerable to destructive pests and depletes the soil. Over the past 40 years fertilizer use has increased approximately 700%. These chemicals often have unintended negative impacts on the environment, including water pollution and eutrophication (which causes dead zones in places like the Gulf of Mexico)1.

In addition the pollution of waterways by pesticides, water reserves are threatened by intensive agriculture. The irrigation required by modern farm systems depletes freshwater resources; agriculture alone accounts for approximately 85% of global consumptive water use (water not returned to the watershed)1. This reduces the water available for human consumption, with obvious negative health consequences.

monoculture
Delicious.

Agricultural intensification has also taken a toll directly on human health. The negative effects of pesticides have been well documented for both farmworkers and consumers and have been linked to a suite of illnesses ranging from cancer to Parkinson’s. The density livestock on industrial farms and their proximity to humans has also increased the risk of infectious disease spread1.

Adding insult to injury.

Now for the irony. Intensifying agriculture through monoculture farming may actually decrease our food security in the long term. Our current practices erode our soil (via deforestation and tillage), giving us less to farm in the future1. And by carpeting the landscape with just a few species, we are creating an ideal habitat for agricultural pests and diseases, making crops vulnerable to outbreaks and epidemics. In America, this is especially true for corn and soy, which span large, connected regions of the contiguous US2. This leaves humanity in a precarious position: although intensive agriculture is unsustainable and destructive, we must increase crop yields to feed our swelling ranks.

The situation is certainly grim, but there is reason for hope. Researchers are gaining a greater appreciation for the fact that agricultural systems are ecosystems, networks of species interactions. By generating an understanding of these relationships, we are taking the first steps toward being able to develop management strategies that enhance the natural capacity of agricultural systems with minimal inputs. This approach has the potential to increase yields without the chemical coating.

References

1. Foley, JA, R DeFries, GP Asner, C Barford, G Bonan, SR Carpenter, FS Chapin, MT Coe, GC Daily, HK Gibbs, JH Helkowski, T Holloway, EA Howard, CJ Kucharik, C Monfreda, JA Patz, IC Prentice, N Ramankutty, & PK Snyder. (2005). Global consequences of land use. Science, 390:570-574.

2. Margosian, ML, KA Garrett, JMS Hutchinson, & KA With. (2009). Connectivity of the American agricultural landscape: Assessing the national risk of crop pest and disease spread. Biosciences, 59:141-151.

3. Pretty, J. (2008). Agricultural sustainability: concepts, principles and evidence. Philosophical Transactions of the Royal Society B, 363:447-465.

Image credit: Attribution: Austin Valley, via Creative Commons