With all the excitement about the “first” case of “mad cow disease” reported in the United States, I thought readers might be interested in some straightforward information about the situation. I am not an expert, but by personal interest and profession I keep up with what is going on as much as I can. Bovine spongiform encephalopathy (BSE) or “mad cow disease” is one of a family of diseases named for the characteristic microscopic appearance of brain tissue. Spongiform encephalopathy, or “prion” (pronounced pree-on), means literally: “brain disease in the form of a sponge,” i.e. full of holes.
The spongiform encephalopathy diseases stretch scientific understanding of disease-causing agents. Prions are abnormally configured (folded) proteins that can cause normally configured protein to reconfigure, resulting in damaged neural tissue. Those who have read Cat’s Cradle by Kurt Vonnegut will note an eerie similarity to “Ice Nine.” A prion is not really a living agent; therefore, it can’t be killed with the techniques used against bacteria and viruses, nor can it be vaccinated against.
Human prion diseases include Creutzfeldt-Jacob disease (CJD) and formerly, kuru. There is also scrapie in sheep, mink encephalopathy, chronic wasting disease of cervids (deer and elk) and BSE. They tend to have a very, very slow onset and are not easily transmissible in general, although eating affected neural tissue can transmit some forms of the disease. They are also thought to be transmitted vertically (from mother to offspring), especially in the case of scrapie in sheep. There is considerable evidence that at least some forms of prion diseases occur spontaneously at very low levels without exposure to any risk factors. CJD in its traditional form in humans is one example. Studies have shown that CJD can appear randomly in human beings, without regard for race, gender, nationality or dietary preferences.
The appearance and spread of BSE in Britain in the early ’90s is generally believed to be related to the widespread practice of feeding livestock rendered products: bone meal, blood meal, meat meal, etc. This practice was banned in the UK, and the incidence of BSE has been declining dramatically. Many people believed that BSE appeared in cattle fed rendered sheep products.
Scrapie has been well established in British sheep for about 200 years. However, clinical attempts to cause BSE by feeding affected sheep products to cattle were not succeedful. Similar to the occurrence of CJD in humans, there is probably random occurrence of spongiform encephalopathy in cattle, and one or more of these cases may have started the outbreak in Britain.
The US appeared to have been spared an outbreak, until December, by virtue of the fact that cattle ranchers didn’t feed very much rendered product back to livestock. The rendered product that was used in feed was treated with a “solvent extraction” process more likely to denature the prions. But if those who believe that sporadic cases of BSE arise in the cattle population are right, it was always only a matter of time before a case showed up.
As the story unfolds, it turns out the cow was imported from Canada and old enough to have been fed rendered cattle material before the ban was in place. Still, the absence of any other cases makes feed transmission questionable, as nearly as I can follow the situation. Organic production of beef eliminates the danger of transmitting BSE through feed. Feeding animal-derived feeds to livestock is strictly forbidden under organic standards. It should also be noted that milk has never been implicated in BSE transmission in any way so dairy products are not a source of concern, whether organic or not.
The media have not widely reported the fact that the cow in question came from a 2,600-cow dry-lot dairy in Eastern Washington. Dry lot means no pasture—cows in a stall all day or with possibly a dirt pile to stand on outside. The calves would not have been raised on the premises and replacements would be purchased from outside. The dairy almost surely would have been using recombinant bovine growth hormone on these cows as well.
US Department of Agriculture (USDA) veterinarians have had a hard time identifying or tracing other related cows. The trail of this cow is so complex and convoluted—it’s taking weeks to find out where she came from, and the USDA may never know where her offspring have gone. Contrast that to the organic dairies I work with where animals spend their entire lives on one farm. I recently interviewed an owner who said they hadn’t bought a cow in 31 years, except a couple 15 or 20 years ago when the children had 4-H cows. When I went out to assist a heifer deliver her first calf, the herds-man said; “We want this one saved. Her mother is one of our best cows!” The calf is on the farm from birth until it goes to slaughter, sometimes after milking for 10 or 12 years. In an industrial dairy, a cow is lucky to make it through three years of milking before she’s “burned out.” Veterinarians just see fewer diseases under organic, human-scale conditions.
If, however, there turns out to be random sporadic cases of BSE in cows, an organic cow could be affected as well as an industrial one. But, with a random occurrence, it would certainly never spread any further than the single case.
During the British outbreak, after the government insisted there was no risk to people, a variant form of CJD (new variant CJD or vCJD) appeared that is thought to be associated with eating BSE-contaminated meat. After hundreds of thousands of bovine cases, there have only been about 140 cases of vCJD so it is clearly not highly transmissible. Since the British outbreak is receding and neurological tissue has been removed from the food chain, the numbers of cases of vCJD have been declining as well.
It is extremely difficult to evaluate risk in a situation like this, but the evidence I see suggests that human risk truly is vanishingly small. One wag in England at the height of the scare calculated that you were more likely to fall over and break your neck putting on your underwear than to contract vCJD. Clearly the risk of contracting it from organic beef in the United States is too small to calculate. One case of BSE does not make an outbreak, but already some of my livestock clients are taking losses. This community of dairy farmers and cattle ranchers hopes the scare passes quickly. I urge you, dear readers, to support farmers, especially organic farmers through this hard time. After the US cut off Canadian beef imports (in my opinion more for political than true health reasons), Canadians rallied around their beef industry and consumption actually increased in some areas. I would like to see that happen here. In my community, at least, most ranchers are good people trying hard to eke a sustainable living out of the land, whether organic or not.
By Joe Snyder, DVM