BSE in the US: 8,929 cow brains examined

The following was extracted from a recent document written by Dr. Gary Pearl (no email account), President-Director Technical Services, Fats and Proteins Research Foundation, 309-829-7744, fax 309-829-5147.

"October 1996 In an independent survey of the State Veterinarians and State Diagnostic Laboratories (G.G. Pearl, FPRF, June 1996), twenty-three states responded. The responding states had submitted a total of 888 specimens to NVSL for BSE confirmation. However, during that same time period (1990 through June 1996), these certified accredited diagnostic laboratories received 8,929 animals exhibiting signs of CNS disorders. Definitive diagnoses were established for other existing CNS diseases or conditions for all of the animals with the exception of the 888. There were no laboratory submissions suggestive of BSE reported. The 888 animals were subsequently determined to be free of BSE. It, therefore, can be determined that the diagnostic laboratory structure in the United States allows for enhanced surveillance of approximately tenfold being reported as actual brain submissions to NVSL. USDA has likewise republished BSE Implications for the US in April 1996 which describes the many components existing in the surveillance program for BSE in the US."

Listserve posted questions for Dr. Pearl:
Q1.  What was the breakdown to specific CNS disorders  for the 8929
animals, ie rabies etc., and what they did they end up with for definite
diagnoses for the 888, if not BSE?

Q2.  What was the exact source of the prion antibody used to perform the
BSE screen (or was it just slides)?

Q3. Were neuromuscular disorders and miscellaneous "downers" considered in
with CNS disorders?

Q4. How big a pool of healthy animals did  the 8929 come out of?  That is,
is there an incidence rate here for CNS disorders?

Q5. Is the full document available online -- sounds like there could be a
broad need to refer to it.
I would recommend caution in interpretion of Dr. Pearl's report. BSE is a particular _strain_ of bovine TSE only known from England. If only that particular strain was sought to the exclusion of other bovine TSEs, then the study addresses mainly whether the US herd has picked up the British strain, not the levels of endigenous US strains (if any) of bovine TSE. There would have been roughly only 50-80 imported cows and later calves seriously incubating British BSE in the US, assuming no amplification, based on import dates and infection levels, as adjusted for under-reporting.

More specifically, the big new Collinge study, 24 Oct 1996 Nature 382, 685-690 (1996), extends and confirms work of Bessen and Marsh on two US strains of TME. If one assumes [repeat, if one assumes] the mink got these from downer dairy cows, then there were at least two very different strains of bovine TSEs possibly prevalent in the US in the late 1980's. TSEs exhibit a tremendous variability in presentation (often not spongiform nor plaque-forming, sometimes affecting blood vessels or lymphoreticular tissue or neuromuscular junctions), so a pathologist trained on imported BSE brain slides might only be ruling out that particular strain in similar breeds.

Note there has been no strain testing yet of US victims of "sporadic" CJD but this can be expected imminently. Strain typing has the potential for definitively identifying the original source of the infection, even if it occurred decades ago. In one scenario, some (presumbably non-mink eating) victims would type out the same as a TME.

There is an opportunity for confusing the public, not to mention media, with language issues: does "mad cow disease" mean bovine TSEs collectively or mean exclusively the British strain BSE? I favor bovine TSE; if BSE is used then the British strain should be further delineated, so ukBSE or some such. Similarly dyTME and hyTME for mink, nvCJD for new variant etc.