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Health & Nutrition
Mad Cow and Foot and Mouth Diseases: Food Safety
Foot and mouth disease is a severe, highly contagious viral disease of wild
and domestic animals. It primarily affects cattle and pigs, but infections can
also occur in sheep, deer, and other cloven-hooved animals.
According to the Centers for Disease Control and Prevention, infections in
humans are extremely rare. The disease has not been reported in the United
States since 1929. However, an outbreak of foot-and- mouth disease is occurring
in the United Kingdom and other Western European countries and has received
considerable attention in the media recently.
The United States Department of Agriculture asserts that the disease has no
implications for the human food chain but does caution that people can spread
the virus to animals because it can remain in human nasal passages for as long
as 28 hours.
"Mad cow disease" or more appropriately bovine spongiform
encephalopathy (B-S-E), is a chronic, degenerative disease that causes progressive
neurological degeneration in cattle. Symptoms are observed in adult cattle
between 2 and 8 years of age after a long incubation period and is always fatal.
The disease was first identified in Great Britain in November 1986 and has been
diagnosed in nine other European countries. The bulk of the 178,000 confirmed
cases worldwide, over 95 percent, have occurred in the United Kingdom. B-S-E is not known
to exist in the United States.
It is suspected that B-S-E originated from scrapie, a degenerative disease
affecting the central nervous system of sheep and goats. Scrapie was first
recognized as a disease of sheep in Great Britain and other Western European
countries more than 250 years ago and has been reported throughout the world.
Only two countries are recognized by the United States as being free of scrapie:
Australia and New Zealand.
Until 1988 rendered carcasses of livestock, including sheep, were fed to
ruminants and other animals as a protein-rich nutritional supplement in the
United Kingdom. Although still disputed, it appears likely that changes in the
rendering process that occurred around 1980 allowed the etiologic agent in
infected carcasses to survive, contaminate the protein supplement, and infect
cattle. Cattle carcasses and carcass wastes were then recycled through the
rendering plants, increasing the levels of the now cattle-adapted pathogen in
the protein supplement and eventually causing a full-scale B-S-E epidemic.
B-S-E belongs to the family of diseases known as transmissible spongiform
encephalopathies (T-S-E's). These progressive, degenerative neurological diseases
are characterized by long, asymptomatic incubation periods of up to several
years. T-S-E's are caused by similar agents, believed to be prions, that produce
spongiform changes in the brain. T-S-E's include scrapie, transmissible mink
encephalopathy, feline spongiform encephalopathy, chronic wasting disease of
deer and elk, and in humans, kuru, Creutzfeldt-Jakob Disease (C-J-D),
Gerstmann-Straussler syndrome, and fatal familial insomnia.
Similar to B-S-E, C-J-D is a rare disease that occurs in humans with an annual
incidence of approximately one case per million population worldwide. C-J-D is
rapidly progressive and invariably fatal. A new variant of C-J-D, v-C-J-D, was found
by scientists in 1996 that could possibly be linked to B-S-E. While it is not
certain how B-S-E may be spread to humans, evidence indicates that humans may
acquire v-C-J-D after consuming B-S-E-contaminated cattle products. Among humans, the
total worldwide number of known v-C-J-D cases is 92, including 88 in the U.K.,
three in France and one in Ireland.
According to the U.S. Department of Health and Human Services, U.S. agencies
have acted quickly with precautionary steps to prevent B-S-E in cattle or v-C-J-D in
humans from occurring in this country. These steps include:
- Prohibiting importation of live ruminant animals and most ruminant products
from all of Europe (U-S-D-A)
- Examining U.S. cattle exhibiting abnormal neurological behavior to test for B-S-E
(U-S-D-A)
- Prohibiting the use of most mammalian protein in the manufacture of animal
feeds given to ruminant animals (F-D-A)
- Recommending that animal tissues used in drug products should not come from a
country with B-S-E (F-D-A)
- Issuing guidelines asking blood centers to exclude potential donors who have
spent six or more cumulative months in the U.K. between 1980 and 1996 from
donating blood (F-D-A)
- Conducting regular surveillance for any cases of v-C-J-D among humans (C-D-C)
- Conducting research on B-S-E, C-J-D, v-C-J-D and related neurological diseases (N-I-H)
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