BSE in the United States
The USDA announced on December 23, 2003 the first diagnosis of
bovine spongiform encephalopathy (BSE or mad cow disease) in the
United States.
BSE is not contagious. It is unlikely that an outbreak
of BSE will occur in North American cattle because the United
States and Canada had already taken action in 1997 to prevent
transmission via contaminated feed. The risk to human health from
BSE is miniscule. However the diagnosis may seriously affect beef
exports from the US.
What is BSE?
Bovine spongiform encephalopathy is a disease of adult cattle
affecting the central nervous system. It also is sometimes referred
to as mad cow disease. Affected cattle develop progressive behavior
changes, abnormal posture, incoordination, reduced milk production
and weight loss. The disease typically occurs in cattle 5 years
of age or older. It is rare for cattle younger than 3 years old
to be affected.
The disease was first diagnosed in Great Britain in 1986. It
soon became apparent that an outbreak was occurring in British
cattle. The epidemic peaked in 1993 at 1,000 cases per week
and has since waned. Currently about 25 cases per week are identified
in Great Britain. BSE has been diagnosed in native cattle in
several other European nations, Japan, Israel, and Canada. The
cow diagnosed with BSE in the United States was imported from
Canada as an adult.
What causes BSE?
BSE is one of a family of similar diseases known as transmissible
spongiform encephalopathies (TSE). Different TSE diseases are
known to occur in several species such as sheep, cattle, deer
and elk, mink, squirrels and man. The cause of TSE diseases
is not known for sure, but a leading theory is that the disease
is transmitted by ingestion of an infectious prion protein.
It is not known how BSE originated. However, it is clear that
the outbreak of BSE in Great Britain and Europe was caused because
in the early 1980s cattle were exposed to a common source of
feed contaminated with the infectious prion protein. Ingestion
of contaminated feed products remains the primary risk factor
for transmission of the disease to cattle. Transmission from
animal to animal is unlikely to occur.
Why has BSE in Europe caused such concern?
In 1996 a possible link was proposed between BSE and a disease
of humans recently observed in Britain. The disease in humans
was a variant form of CJD (Creutzfeldt-Jakob Disease), a fatal
TSE of man. The link between BSE and new variant CJD (vCJD)
is likely. To date there have been 143 definite or probable
cases of vCJD diagnosed in people from the United Kingdom. The
link between vCJD and consumption of BSE-contaminated beef was
devastating to the European beef industry although consumer
confidence in beef is returning.
