More than 1,200 head of Texas cattle are under quarantine because a small amount of ruminant meat and bone meal was accidentally mixed into 22 tons of feed, in violation of an FDA rule. The rule was implemented in 1997 as a precautionary measure, although mad cow disease (bovine spongiform encephalopathy or BSE) has so far not been detected in American cattle.
BSE is believed to be caused by prions, proteins that have assumed an abnormal three-dimensional configuration. Normal proteins in contact with prions also assume this structure, leading to clumps of protein that destroy the brain. The agent is smaller than most viral particles and is highly resistant to heat, ultraviolet light, ionizing radiation, and common disinfectants.
Affected cattle display changes in temperament, becoming nervous or aggressive, are uncoordinated, and have difficulty getting up. Death occurs within 2 to 6 months. The incubation period ranges from 2 to 8 years.
It was originally assumed that BSE was derived from scrapie, a 200-year-old disease in sheep that is not transmitted to humans. The current view is that BSE emerged in the 1970s from a genetic mutation in a single cow.
Reassurances based on a species barrier were ill-founded. Mice, for example, were thought to be highly resistant to prions derived from hamsters because they developed no clinical signs within their 2-year life spans. The brains of the apparently healthy mice, however, contained aberrant mouse proteins, and extracts of these brains made other mice ill (Science 2000;289:1663-1665).
Domestic cats have gone down with a BSE-like illness, and there is a similar chronic wasting disease in deer and elk. The Canadian government has killed 1,700 domesticated elk. Powdered "velvet antler" from elk, widely sold worldwide as a health food supplement, might possibly be a vehicle to transmit disease.
BSE is believed to be the culprit in 81 human cases of variant Creutzfeldt disease (vCJD) over the past 15 years in Britain. Average age of the victims was 28; the sporadic form of CJD generally affects persons over the age of 60. Brain pathology is recognizably that of CJD, but large aggregates of prion protein are found. The condition is untreatable and fatal within about 13 months. Incidence in Britain has been increasing by about 23% per year.
Britain has slaughtered 176,000 cattle. Panic is spreading through Europe, as cases begin to appear in areas believed to be pristine. The "purchase for destruction" program launched by the European Union anticipates buying and incinerating up to 2 million head of cattle by the end of June. Carcasses are being frozen until they can be rendered into meal, which will have to be warehoused until it can be incinerated. It could take years to build the incinerator due to environmentalist opposition. Irish taxpayers will probably pay $170 million in storage costs (P Doyle, AP, 1/21/010).
French consumer groups are up in arms over regulations that permit a 0.3% level of meat in cattle feed - an amount that could result from use of trucks that had previously carried meat for human consumption. This tolerance level is said to be a "scandal." On the other hand, sending tons of prime beef up in smoke in a hungry world has been called a "shame and a disgrace."
The whole concept of recycling animal protein to supplement feed is in question-with the potential for devastating economic consequences. Turkey farmers claim to have been saved from financial ruin when Norbest and Moroni Feed Cooperative started grinding up turkey claws, bones, and other remains to add to feed (WorldNetDaily 11/25/98). While Salmonella is a major problem in poultry, prion disease has not been reported. Still, the British BSE Inquiry Report ( www.bse.org.uk) concludes: "BSE could have arisen anywhere and spread wherever animal protein is recycled. Other[s] should ponder our experience" (Science 2000;290:911-913).
The most infective parts of the carcass are brain and spinal tissue. Mechanical methods of stripping meat from the spine could allow traces of spinal cord to contaminate the meat. The entire intestine is now being classified as "specified risk material" in Ireland. Liver is 1,000 times more infective than muscle.
Despite a serious blood shortage, and lack of evidence of blood-borne transmission of vCJD, the FDA proposes to ban blood donors who have spent more than 10 years in Western Europe, or 6 months in the UK, since 1980. The FDA will not, however, recall vaccines containing bovine products from countries reporting BSE. Most manufacturers have voluntarily agreed to use materials only from BSE-free sources in the future. The British BSE Inquiry considered the possibility that some persons acquired vCJD through immunization. The investigation is hampered by the fact that "systematic records of the action taken in response to BSE in respect of individual medical products are lacking." The meat industry responded more rapidly than the pharmaceutical industry and related government agencies. A comprehensive assessment of BSE-related issues in vaccines is underway, but it is not known when a report will be made public (Nature 2000;408:3-5).
The CDC calls the risk of vCJD from vaccines-a sacred cow?-"theoretical and remote." The Public Health Service recommends that vaccinations continue on schedule, with no preference being given to one product over another based on the source of bovine materials. "Failure to obtain the recommended vaccinations with licensed vaccines poses a risk for serious disease" (MMWR 2000;49:1137-1139).
In deriving its risk estimates, the FDA assumes that, based on work with sheep, bovine brain is 100 million times as infective as muscle. Infected bovine brain contains 10 million infectious units per gram when administered intracerebrally to other cattle. Infectivity rate is estimated to be 200-fold lower for material administered intramuscularly. Other assumptions: a 1 in 1,500 incidence of BSE in fetal calves whose serum is used to derive viral seed and cell banks; a 1 in 10,000 incidence in cows used to prepare nutrient broth; no species barrier; and inability of the BSE agent to replicate in tissue cultures, based on numerous failed attempts to get it to do so. An upper level of risk between 1 in 40 billion to 1 in 40 million doses of vaccine has been calculated (see www.fda.gov/cber/BSE/risk.htm).
Vaccines that contain components from FDA-listed countries with BSE include: Aventis Pasteur S.A.'s Haemophilus influenzae type b conjugate vaccine, ActHIB®, also marketed as OmniHIBTM; North American Vaccine Inc.'s diphtheria, tetanus, acellular pertussis (DTaP) vaccine; SmithKline Beecham Biological's DTaP vaccine; CertivaTM tetanus toxoid; Infanrix® diphtheria toxoid; and hepatitis A vaccine, Havrix®. Vaccines in which the source of bovine-derived materials is unknown include Aventis Pasteur S.A.'s inactivated polio vaccine, IPOL®; BioPort's anthrax and rabies vaccine; and Lederle Laboratories' pneumococcal polysaccharide vaccine, PNU-IMUNE® 23. Vaccines using bovine material from USDA listed or unknown sources only for the master seeds are not identified because the FDA has determined that the seeds do not need to be re-derived (www.fda.gov/cber/BSE/bse.htm).
DDP has often been critical of the "Precautionary Principle," especially with regard to entities with a half-life. For entities that reproduce and have a doubling time, however, mistakes can be far more devastating.
The two-day weekend lecture program, July 14-15, will follow a July 13 tour of the Nevada Test Site, now celebrating its 50th anniversary. The July 16 tour of Nellis Air Force Base will include the training facility and Thunderbird Museum (but no air shows are planned). Pre-registration is mandatory for security reasons. Foreign nationals require State Dept. approval to visit the AFB and 60-90 days notification for admission to the NTS. The meeting site is the Sahara Hotel at the very special weekend rate of $79 (Friday and Saturday) and weekday rate of $32. Reserve a place NOW by calling DDP at (520) 325- 2680 and the Sahara at (888) 696-2121.
DDP, 1601 N. Tucson Blvd. Suite 9, Tucson, AZ 85716, (520)325-2680