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Bovine spongiform encephalopathy (BSE), also known as the mad cow disease, is a progressive, lethal central nervous
system disease of cattle. It is characterized by the appearance in neurons in
the brain of affected cattle of vacuoles, clear holes, that give the brain the
appearance of a sponge--thus the term or spongiform was derived. As part
of Nevada's surveillance program, brain tissue from downer cows are test for
BSE. The incubation period is from 2 to 8 years. Following the
onset of clinical signs, the animal's condition deteriorates until it either
dies or is destroyed. This process usually takes from 2 weeks to 6 months. Most
cases in Great Britain have occurred in dairy cows between 3 and 6 years of age.
Cattle affected by BSE exhibit progressive degeneration of
the nervous system. Affected animals may display changes in temperament, such as
nervousness or aggression, abnormal posture, incoordination and difficulty in
rising, decreased milk production, or loss of body weight despite continued
appetite. Affected cattle die. The causative agent of the disease is not
completely characterized. There is currently no treatment or vaccine available.
BSE is one of several diseases catagorized as Transmissible
Spongiform Encephalopathies (TSEs). The disease is believed to be
caused by a "self-replicating" protein (a prion; PrPSc)
rather than a bacterium or virus. Bioassays have identified the
presence of the BSE agent in the brain, spinal cord, retina, dorsal root ganglia
(nervous tissue located near the backbone), distal ileum, and bone marrow of
cattle experimentally infected with this agent by the oral route. Meat,
blood and milk have not been shown to carry the infective agent. Measures have
been taken to exclude tissues that carry the infective agent (i.e. brain &
nervous tissue) from the food supply.
Currently, there is no test to detect the disease in a live
animal; veterinary pathologists confirm BSE by postmortem microscopic
examination of brain tissue or by the detection of the abnormal form of the
prion protein. BSE is so named because of the spongy appearance of the brain
tissue of infected cattle when sections are examined under a microscope.
The U.S. Department of Agriculture's (USDA)
Animal and Plant Health Inspection Service (APHIS)
has banned importation of live cattle or meat products from BSE-infected
countries since 1989 and is conducting surveillance for BSE to ensure that it
does not become established in the United States. In 1997, the
FDA
has also been put in place a ruminant to ruminant feed ban similar to that in
Great Britain as an additional safeguard.
In Nevada, inspections are conducted at feedlots, dairies, feed mills and
mineral operations to insure that mammalian protein is not being fed to
ruminants. The feed law prohibits the use of mammalian protein in ruminant
feeds. Follow-up inspections are conducted as necessary and educational material
is provided in English and Spanish. This program is funded under a grant from
the Federal Food and Drug Administration.
The United States was free of BSE until December 23,
2003 when positive test results were reported from a single cow in Washington
State. This case involves a 6.5 year-old Holstein cow, which was identified as a
downer cow on antemortem inspection at the time of slaughter, and was tested for
BSE as part of USDA’s targeted surveillance program.
Useful Links:
APHIS.USDA.GOV -
Bovine Spongiform Encephalopathy (BSE)
CDC - BSE (Bovine Spongiform
Encephalopathy, or Mad Cow Disease
World Health
Organization - Bovine spongiform encephalopathy
FASonline - Bovine Spongiform
Encephalopathy (BSE) |
