1 figure omitted
On December 23, 2003, the U.S. Department of Agriculture (USDA) made
a preliminary diagnosis of bovine spongiform encephalopathy (BSE) in a single
"downer" (i.e., nonambulatory disabled) dairy cow in Washington state. On
December 25, this diagnosis was confirmed by the BSE international reference
laboratory in Weybridge, England. This report summarizes the findings of the
initial investigation of this case and describes the public health prevention
measures adopted by USDA to protect the human food supply. The occurrence
of BSE in the United States reinforces the need for physicians to be aware
of the clinical features of variant Creutzfeldt-Jakob disease (vCJD) and to
arrange for brain autopsies in all decedents with suspected or probable CJD
to assess the neuropathology of these patients.
The BSE-positive cow was aged 6.5 years when it was slaughtered on December
9. Before slaughter, the cow was nonambulatory; its condition was attributed
to complications from calving. The animal was examined by a USDA Food Safety
and Inspection Service (FSIS) veterinary medical officer both before and after
slaughter. After examination, the carcass was released for use as food for
human consumption. Tissues (e.g., brain, spinal cord, and small intestine)
considered to be at high risk for the transmission of the BSE agent were removed
from the cow during slaughter and sent for inedible rendering (often used
for nonruminant animal feed). Because the cow was nonambulatory at slaughter,
brain tissue samples were taken by USDA's Animal and Plant Health Inspection
Service (APHIS) as part of its targeted surveillance for BSE. On December
23, a presumptive diagnosis of BSE was made, and the herd to which this cow
belonged was placed under a state hold order. USDA, in collaboration with
state and other federal animal and public health agencies, industry representatives,
and the Canadian Food Inspection Agency (CFIA), initiated investigations of
potentially exposed cattle and regulated products.
On December 24, FSIS recalled beef from cattle slaughtered in the same
plant on the same day as the BSE-positive cow. Some of the beef subject to
the recall had been shipped to several establishments, which processed it
further. Meat products manufactured from the recalled meat were distributed
primarily to locations in Oregon and Washington, with smaller quantities distributed
to locations in California, Idaho, Montana, and Nevada. FSIS continues to
verify the distribution and control of all recalled products.
The U.S. Food and Drug Administration (FDA) and inspectors from Oregon
and Washington have located all known potentially infectious rendered products
from the BSE-positive cow. The rendering plants that processed this material
have placed a voluntary hold on all known potentially infectious products,
none of which had left the control of the companies or entered commercial
distribution as of January 7, 2004. FDA continues its investigation of all
regulated products related to the BSE-positive cow.
APHIS, in collaboration with CFIA, traced the birth of the BSE-positive
cow to a farm in Alberta, Canada. On January 6, USDA and CFIA announced that
DNA evidence had confirmed this traceback to Canada with a high degree of
certainty. This line of investigation indicates that the BSE-positive cow
was one of 82 animals from a Canadian herd cleared for shipment to the United
States; 81 of the cattle listed on the Canadian animal health certificate
entered the United States on September 4, 2001, through Oroville, Washington.
These cattle are being traced to determine their disposition or current location.
The BSE-positive cow gave birth to two live calves while in the United States.
The first is a yearling heifer on the same farm as the BSE-positive cow. The
second, a bull calf, was in a group of calves at another location, a calf-feeding
operation that also was under a state hold order. Because the bull calf could
not be identified definitively, APHIS completed the elimination of all calves
at this site on January 6. Since the epidemiologic investigation began, APHIS
has developed criteria for determining additional cattle at risk for BSE that
should be eliminated.
On December 30, USDA announced additional safeguards to further minimize
the risk for human exposure to BSE in the United States (see box). Beginning immediately, FSIS has prohibited the use
of downer cattle for food for human consumption. Through its emergency rule-making
powers, FSIS will take additional actions that will become effective on their
publication. Planned actions include the required removal of "specified risk
materials" (i.e., high-risk materials) from animals aged >30 months at the
time of slaughter and withholding the USDA "inspected and passed" mark until
negative BSE test results are received for any animal tested. To enhance the
speed and accuracy of the response to animal health threats such as BSE, APHIS
is working to implement a national identification system to track animals
of various species through the livestock marketing chain. USDA also will appoint
an international panel of scientists with BSE expertise to provide an objective
review of the response to the identification of the BSE-positive cow described
in this report and to identify areas for potential improvement of current
BOX. Safeguards proposed by the U.S. Department of
Agriculture (USDA) to minimize the risk for exposure to the bovine spongiform
encephalopathy (BSE) agent — United States, December 30, 2003
USDA's Food Safety and Inspection Service (FSIS)
has announced an immediate ban on the use of nonambulatory disabled ("downer")
cattle for human food consumption.
FSIS inspectors will not mark cattle carcasses
tested for BSE as "inspected and passed" until negative test results are received.
FSIS will prohibit the use in the human food supply
(including advanced meat recovery [AMR]*) of "specified risk materials" (i.e.,
high-risk materials), including the skull, brain, trigeminal ganglia, eyes,
vertebral column, spinal cord, and dorsal root ganglia of cattle aged >30
months and the tonsils and small intestine of cattle of all ages.
FSIS also will prohibit the presence of brain,
spinal cord, trigeminal ganglia, and dorsal root ganglia from cattle aged
<30 months in meat produced by AMR.
To reduce the risk that portions of the brain are
not dislocated into the tissues of the carcass as a consequence of stunning
cattle before slaughter, FSIS will ban airinjection stunning.
FSIS will prohibit the use of mechanically separated
beef† in the human food supply.
*An industrial process that removes muscle tissue from the bone of beef
carcasses under high pressure without incorporating bone material when operated
properly; product may be labeled as "meat."
†A meat food product that is finely ground to a paste- or batter-like
consistency and that results from the mechanical separation and removal of
most of the bones from the attached skeletal muscle of cattle carcasses and
parts of carcasses; may not be labeled as "meat" but rather as "meat food
Animal and Plant Health Inspection Svc; Food Safety and Inspection Svc,
U.S. Dept of Agriculture. U.S. Food and Drug Administration. Div of Vital
Statistics, National Center for Health Statistics; Div of Viral and Rickettsial
Diseases, National Center for Infections Diseases, CDC.
BSE is a progressive, fatal neurologic disorder of cattle and is classified
as one of the transmissible spongiform encephalopathies, a group of diseases
of animals and humans believed to be caused by abnormally folded proteins
called prions. BSE was first identified in 1986 in the United Kingdom (UK),
where it caused a large outbreak among cattle.1 Although the source
of the BSE epizootic agent is uncertain, feeding cattle BSE-contaminated meat-and-bone
meal is the major contributory factor to the amplification of BSE among cattle.2 Since 1986, BSE cases have been identified in 20 European countries,
Japan, Israel, and Canada. Since BSE surveillance was initiated in the United
States in 1990, USDA has tested brain tissue from approximately 57,000 cattle,
targeting those at high risk for BSE (e.g., downer cattle and cattle with
neurologic signs); the case described in this report represents the first
identification of BSE in the United States. Whether an epidemiologic link
exists between this BSE case traced to Canada and the previous case reported
in Canada is not known.
Epidemiologic and laboratory evidence suggests that the BSE agent has
been transmitted to humans via consumption of BSE-contaminated cattle products,
causing vCJD.1 However, the risk for acquiring vCJD from consumption
of BSE-contaminated product is low, presumably because of a "species barrier"
that provides substantial but incomplete protection against development of
vCJD. In the UK, where an estimated one million or more cattle probably were
infected with BSE, cases of vCJD continue to be reported; however, the number
of cases of vCJD remains small, with 148 probable and confirmed vCJD cases
identified as of January 7, including those of three persons residing in Ireland,
Canada, and the United States who are believed to have been exposed to BSE
in the UK.1,3 Seven additional cases not directly linked to the
BSE outbreak in the UK also have been reported (six in France and one in Italy).
In the United States, the feeding of rendered cattle products to other
cattle has been prohibited since 1997, and the importation of cattle and cattle
products from countries with BSE or considered to be at high risk for BSE
has been prohibited since 1989; these measures have minimized the potential
exposure of animals and humans to the BSE agent.4 The additional
safeguards described in this report should further reduce the risk for acquiring
Substantial clinical and epidemiologic differences exist between vCJD
and the more commonly occurring classic form of CJD recognized in the United
States for decades before the emergence of BSE (Table ).
Although strong epidemiologic and laboratory evidence indicates that vCJD
is linked causally with BSE, no exogenous source of infection has been identified
for approximately 85% of classic CJD cases.5 The median age at
death of classic CJD patients in the United States is 68 years, compared with
28 years for vCJD patients. The age distribution of these deaths illustrates
that most vCJD occurs in age groups in which classic CJD is rare (Figure)
(RG Will, M.D., National CJD Surveillance Unit, Edinburgh, Scotland, personal
communication, 2004). In addition, the median duration of illness before death
for classic CJD patients in the United States is 4-5 months, compared with
13-14 months for vCJD patients.6 Patients with vCJD often have
prominent early behavioral or psychiatric manifestations and painful sensory
symptoms, with neurologic signs such as myoclonus and extrapyramidal dysfunction
being delayed for several months after illness onset.6 The characteristic
electroencephalographic pattern of periodic sharp waves observed in classic
CJD patients is absent in patients with vCJD. A characteristic high signal
in the posterior thalamus on T2- and diffusion-weighted magnetic resonance
imaging (the "pulvinar sign") is demonstrated in >75% of vCJD patients, and
in the appropriate clinical context, is highly indicative of a vCJD diagnosis.7
Confirmatory diagnosis of vCJD and classic CJD requires pathologic examination
of brain tissue obtained at autopsy or biopsy. The neuropathology in vCJD
is distinguished by the presence of numerous deposits of kuru-type plaques
surrounded by vacuoles (i.e., "florid plaques") in the cerebellum and cerebrum
and the marked accumulation of the pathologic protease-resistant prion protein
on immunohistochemical (IHC) analysis.8 Prions are detected readily
by IHC analysis in lymphoid tissues (e.g., appendix, lymph nodes, spleen,
and tonsils) of vCJD patients, but not in classic CJD patients.9 All
persons with vCJD tested as of January 2004 have had methionine homozygosity
at the polymorphic codon 129 of the prion protein gene, indicating that persons
who do not carry this genotype (comprising the majority of the general population)
appear to have increased resistance to vCJD.
Since 1996, CDC has used several mechanisms to conduct surveillance
for classic CJD and vCJD in the United States.10 CDC reviews national
multiple cause-of-death data to monitor the epidemiology of CJD in the United
States. CDC, in collaboration with state and local health departments, investigates
CJD cases in persons aged <55 years to identify cases of possible vCJD.
In addition, CDC assists routinely in the investigation of suspected cases
of vCJD spontaneously reported by health-care providers. During 1996-1997,
in collaboration with the American Association of Neuropathologists, CDC established
the National Prion Disease Pathology Surveillance Center (NPDPSC) at Case
Western Reserve University, Cleveland, Ohio. NPDPSC provides advanced neuropathologic
and biochemical diagnostic services free of charge to U.S. physicians and
state and local health departments. These surveillance efforts have not detected
any cases of indigenous vCJD in the United States.
The emergence of BSE in the United States reinforces the need for physicians
to be aware of the clinical features of vCJD in all patients, regardless of
age, who report with distinguishing characteristics (Table 2). Because testing
brain tissue permits the most definitive diagnosis of all forms of CJD and
identification of emerging forms of the disease, including vCJD, CDC encourages
physicians to arrange for brain autopsies in all decedents with suspected
or diagnosed CJD and to use the free services of NPDPSC to assess the neuropathology
of these patients. Information about these services is available from NPDPSC
at http://www.cjdsurveillance.com or from CDC, telephone 404-639-3091.
References: 10 available
Bovine Spongiform Encephalopathy in a Dairy Cow—Washington State, 2003. JAMA. 2004;291(5):553–555. doi:10.1001/jama.291.5.553