Another outlook on the same subject. Credit goes to Livestock Weekly from January 22, 2004. This issue is important enough that I decided to paste it here since I was having trouble linking it for everybody.
BSE, “Variant” CJD Statistics Showing Less Fearsome Picture
Hard on the heals of the first U.S. “mad cow” discovery comes a reassuring British report that cases of the human version appear to have peaked and may fall dramatically short of early projections. Tucked away in the verbiage is a tantalizing fact that suggests the whole issue may prove to have been wildly overblown.
Initial projections from British scientists when the first human cases surfaced in the mid-1990s indicated that literally thousands of Brits would be dying of “variant” Creutzfeldt-Jakob disease by now and that as many as half a million cases would eventually develop, all because of widespread exposure to tainted tissues from cattle with bovine spongiform encephalitis, so-called “mad cow” disease.
Statistics published recently by the U.K. Department of Health, however, show that only 139 deaths have occurred so far and that new cases are on the decline. Deaths last year totaled 18, down from 28 as recently as 2000, and the most current figures project no more than 40 additional cases over the next three-quarters of a century.
As tragic as any death is, far more people die each year of peanut allergies.
The new numbers represent quite a statistical correction in such a short timespan, especially given that the first researcher to propose a link between vCJD and “mad cow” was still warning as recently as 2000 that “thousands of people” soon would be “going slowly and painfully mad before dying.”
The British government took quick steps to counter what was assumed to be the mode of transmission, for one thing. The U.K. slaughtered tens of thousands of cattle infected by or thought to have been exposed to BSE. It also imposed a ban on all bovine brain and spinal cord material in the human food chain, as well as any part of cattle more than 30 months of age. In addition, in an effort to stem further bovine infections, the U.K. banned ruminant-derived products from feed, the suspected vector between diseased animals and healthy ones.
Other factors may have been at work as well, however. The Department of Health report notes — almost in passing — that every human victim of vCJD so far shares a pre-existing, inherited genetic trait common to only a little more than a third of the general population.
The trait is a mutation of a gene relating to “prions,” one form of which is the infectious agent for BSE and other “spongiform encephalopathies.” All vCJD victims to date have been found to possess dual copies of the gene, meaning they inherited the mutation from both parents.
Scientists by nature and training are loathe to issue statements without equivocating baggage, so most studies and analyses of the vCJD-gene link include a caveat warning that the trait in question may only hasten incubation and that victims without the mutated gene may appear in future years. That, of course, is pure speculation, whereas the positive link is documented.
The mutation in question is also associated with the “sporadic” or pre-BSE version of CJD, as well as similar rare prion-based diseases such as kuru, and has even been linked to Alzheimers. No other condition, however, has been found to occur exclusively among patients with dual copies of the gene. Such exclusivity, in fact, is almost unheard-of in any medical condition aside, perhaps, from the fact that no man has ever contracted ovarian cancer or woman prostate cancer.
Studies in recent years have also shown that the overall infectivity of BSE is much less than originally feared. Simply stated, it takes much more infected material than originally assumed to transmit the infection to another victim — “the dose makes the poison.” That means a few stray prions lurking in a packing plant or tucked away in the bowels of a feed mill that processed ruminant-derived meal at some point pose a negligible threat.
And some researchers are even questioning the core assumption that “mad cow” disease has anything whatsoever to do with vCJD.
A paper published in the British Medical Journal edition of October 2001 evaluates the assumption based on long-respected epidemiological criteria for establishing cause and effect. It finds the BSE-vCJD “connection” lacking — or nonexistent — in virtually every specific.
The paper is the work of Scottish surgeon Dr. George A. Venters, former Chairman of the British Medical Association's Public Health Committee. Venters outlines the criteria that epidemiologists use to evaluate evidence linking a given disease to its supposed cause, then applies each of those criteria to the case of BSE and vCJD.
In some instances, he finds the evidence entirely lacking or notes that it may not be available for years. “Strength of association” is one example; there is no way to measure “details of individuals’ exposures” to infectious prions, for instance. Likewise, the “dose-response relation” for humans is unknown. “Reversibility” is another criterion, and Venters points out that the assumed BSE-vCJD link “will be falsified” only “as and when the disease occurs in people born after the bovine spongiform encephalopathy prion has been eliminated from the human food chain…”
In other words, if people continue to contract the disease after the supposed cause no longer exists, the link will definitely be broken — but that will take time.
Meanwhile, he assesses the other criteria, beginning with “biological plausibility.” Venters points out that there is “no direct evidence” that the BSE prion is infectious to humans, whereas “there is evidence for a robust species barrier between humans and prions from ungulate species.” For one thing, he notes, “Prions produced in ungulates and humans have different sequences of amino acids.” He adds that ingestion, the assumed mode of transmission, is “an inefficient route” for prions aside from cannibalism — where there is, obviously, no species barrier to overcome.
Venter thus concludes that “Infection of humans from eating the (BSE) prion is therefore unlikely.”
Another criterion is “specificity.” Venter explains that “prion infection differs from the conventional understanding of the infectious process” in that “cells can only produce prion specific to the species they belong to.”
A human E.coli infection, for instance, can be traced to contaminated food because the same bacteria can be found in both the victim and the tainted source. However, Venter points out, the BSE prion itself “can never be detected in human brains or in any species other than cattle.”
Researchers instead have attempted to link the bovine and human diseases through similar damage to brain tissues, though that, too, is of limited value because brain tissues themselves differ between species. Venter says those who argue the connection are reduced at best to pointing out “similarities” in “physico-chemical properties and strain typing in laboratory experiments.”
For that reason, he concludes, “the specificity of the link between the prion and the disease can only be inferred and remains an open question.
“Given that it is impossible to prove that the (BSE) prion is infectious to humans,” Venter continues, “evidence for the case has to be indirect,” and this is where proponents of the theory may have fallen victim from the beginning to wishful thinking or vested interests.
“The evidence that has been amassed” so far, Venter chides, “is directed towards confirming the hypothesis rather than testing it.” In other words, those who promote the idea of such a link concentrate their efforts on shoring up their position rather than challenging it to see if it can stand on its own.
Most damning from an objective scientific perspective is Venter’s flat assertion that “salient contrary information has been either played down or ignored.”
What supposedly sets “new variant” CJD apart from the traditional disease, for example, is the fact that it tends to strike young victims whereas the conventional wisdom holds that the original version strikes only in middle age or later. Venter points out, however, that the first case of “traditional” CJD, described by German researcher Creutzfeldt himself more than 80 years ago, was in a 23 year-old victim. So much for a “new” variant.
The idea that CJD is limited to older patients, in fact, didn’t become popular until proposed decades later by the disease’s second namesake, Jakob. To support his position, Jakob had to virtually ignore Creutzfeldt’s pioneer case.
Venter adds — pointedly — that the paper claiming the existence of a “new” disease and linking it to BSE also ignored Creutzfeldt’s case and likewise ignored similarities between the “new variant” of CJD and the South Pacific disease kuru, spread within a primitive tribe by cannibalism. It cited kuru as a prion disease spread by ingestion, Venter notes, but only as a way to support the idea that “variant” CJD could be spread through food.
Kuru was thus cited where it was useful to the hypothesis, but “the possibility of them being the same disease was not raised,” he says, one example of “contrary information” being “either played down or ignored.”
He cites several other examples in which “quality of evidence,” a key criterion, is suspect, and concludes that evidence overall “is of variable quality” and “seems to have been selectively developed” along the lines of a fallacious “belief that multiple pieces of suspect or weak evidence provide strong evidence when bundled together.”
So why is BSE linked to vCJD?
For that, Venter turns to the “temporality” criterion, which essentially ties the two diseases together by virtue of their timing.
The “new variant” was discovered shortly after the epidemic of BSE in British cattle, Venter explains, so researchers attempted to link them.
Unfortunately, he continues, “To prove that a disease is new, it is necessary to review and legitimately reject other possibilities,” and this the linkage proponents failed to do.
Specifically, he charges, they failed to rule out kuru and/or Creutzfeldt’s original encephalopathy case. Venter notes “clinical and neuropathological features” common to vCJD and kuru as well as to the Creutzfeldt case. There are differences as well, he concedes, but these “may be more of degree than of kind, in that survival of patients with new variant Creutzfeldt-Jakob disease is likely to be longer because they will generally have received better health care than was available to people with kuru.”
A second element of “temporality” is what Venter terms the “pattern of infection relative to exposure,” and he finds the link weak here, as well.
Venter notes that all food-borne illnesses follow a common pattern or “curve” in their distribution. “The shape of this curve holds true for foodborne infections no matter whether the incubation period is days,” as for E. coli, “or years, as is the case for prions,” he insists. That curve would have followed the BSE infection rate in cattle, he contends, if that were the source of vCJD.
But it doesn’t.
Venter notes that vCJD cases “have been appearing since 1994,” but that “their rate of increase since then falls far short of what would be expected if this was a foodborne infection.”
Given its weaknesses, he terms the “temporality” connection “at best uncertain.”
Venter concludes with the observation that scientists have been trying to draw boundaries around traditional or “sporadic” CJD ever since Creutzfeldt’s first report more than eight decades ago, and those boundaries have been repeatedly adjusted.
He accepts the idea that “variant” CJD is “a different disease” from “sporadic” CJD, but questions “whether it is different from kuru or from Creutzfeldt’s original case.” This, he says, remains to be determined and will only be “clarified with the passage of time.”
Meanwhile, Venter says, “I believe the evidence now casts serious doubt on the case for a causal link between bovine spongiform encephalopathy and ‘new’ variant Creutzfeldt-Jakob disease,” adding that “The medical profession should, at least, be publicly debating this as an issue.”