Questions and Answers
Regarding Bovine Spongiform Encephalopathy (BSE or Mad Cow Disease)
and Creutzfeldt-Jakob Disease (CJD)

What is bovine spongiform encephalopathy?
Bovine spongiform encephalopathy (BSE) is a progressive neurological disorder of cattle that results from infection by an unconventional transmissible agent.

Through the end of November 2003, more than 183,000 cases of BSE were confirmed in the United Kingdom alone in more than 35,000 herds. Regularly updated numbers of reported BSE cases, by country, are available on the website of the Office International Des Epizooties at: http://www.oie.int/eng/info/en_esb.htm.

The BSE epidemic in the United Kingdom peaked in January 1993 at almost 1,000 new cases per week. The outbreak may have resulted from the feeding of scrapie-containing sheep meat-and-bone meal to cattle. There is strong evidence and general agreement that the outbreak was amplified by feeding rendered bovine meat-and-bone meal to young calves.

The nature of the transmissible agent is unknown. Currently, the most accepted theory is that the agent is a modified form of a normal cell surface component known as prion protein. The pathogenic form of the protein is both less soluble and more resistant to enzyme degradation than the normal form.

Is BSE occurring in the United States?
On December 23, 2003, the U.S. Department of Agriculture (USDA) announced a presumptive diagnosis of bovine spongiform encephalopathy (BSE, or "mad cow" disease) in an adult Holstein cow from Washington State. Samples were taken from the cow on December 9 as part of USDA's BSE surveillance program. The BSE diagnosis was made on December 22 and 23 by histopathology and immunohistochemical testing at the National Veterinary Services Laboratory, Ames, Iowa. The diagnosis was confirmed by an international reference laboratory in Weybridge, England, on December 25. Preliminary trace-back based on an ear-tag identification number suggests that the BSE-infected cow was imported into the United States from Canada in August 2001.

Is BSE a foodborne hazard in the United States?
Strong evidence indicates that BSE has been transmitted to humans primarily in the United Kingdom, causing a variant form of Creutzfeldt-Jakob disease (vCJD). In the United Kingdom, where over 1 million cattle may have been infected with BSE, a substantial species barrier appears to protect humans from widespread illness. As of December 1, 2003, a total of 153 vCJD cases had been reported worldwide; of these, 143 cases had occurred in the United Kingdom. The risk to human health from BSE in the United States is extremely low.

Is there any monitoring of the incidence of Creutzfeldt-Jakob disease in the United States?
Yes. The possibility that BSE can spread to humans has focused increased attention on the desirability of enhancing national surveillance for Creutzfeldt-Jakob disease (CJD) in the United States.

The Centers for Disease Control and Prevention (CDC) monitors the trends and current incidence of CJD in the United States by analyzing death certificate information from U.S. multiple cause-of-death data, compiled by the National Center for Health Statistics, CDC. A summary of these data was published in the Journal of the American Medical Association on November 8, 2000 (Volume 284, No. 18, pp. 2322-3). and in Clinics of Laboratory Medicine in December 2002 (Volume 22, pp. 849-62).

The average annual CJD death rate in the United States has remained relatively stable at about one case per million population per year. In addition, CJD deaths in persons aged <30 years in the United States remain extremely rare (<1 case per 100 million per year). In contrast, in the United Kingdom, over half of the patients who died with variant CJD were in this young age group.

What is the variant form of CJD that the experts in the United Kingdom believe might be related to the BSE outbreak in cattle?
In contrast to the classic form of CJD, the variant form in the United Kingdom predominantly affects younger persons (median age at death around 29 years) and has atypical clinical features. These atypical features include prominent psychiatric or sensory symptoms at the time of clinical presentation or early in the course of the illness, delayed onset of neurologic abnormalities, duration of illness of at least 6 months, and a diffusely abnormal non-diagnostic electroencephalogram.

The characteristic neuropathologic profile of variant CJD includes, in both the cerebellum and cerebrum, numerous kuru-type amyloid plaques surrounded by vacuoles and prion protein (PrP) accumulation at high concentration indicated by immunohistochemical analysis.

Recently published data indicate that the epidemic of variant CJD in the United Kingdom may have already reached a peak. A listing of monthly updated numbers of variant CJD cases in the United Kingdom is available at: http://www.doh.gov.uk/cjd/cjd_stat.htm.

Is there evidence directly linking this newly recognized variant of CJD to BSE exposure?
There is strong epidemiologic and laboratory evidence for a causal association between variant CJD and BSE. The absence of confirmed cases of variant CJD in other geographic areas free of BSE supports a causal association.

In addition, the interval between the most likely period for the initial extended exposure of the population to potentially BSE-contaminated food (1984-1986) and onset of initial variant CJD cases (1994-1996) is consistent with known incubation periods for CJD.

An experimental study reported in June 1996 showed that three cynomologus macaque monkeys inoculated with brain tissue obtained from cattle with BSE had clinical and neuropathological features strikingly similar to those of variant CJD (Nature 1996;381:743-4).

A study published in 1996 indicated that a Western blot analysis of infecting prions obtained from 10 variant CJD patients and BSE-infected animals had similar molecular characteristics that were distinct from prions obtained from patients with other types of CJD (Nature 1996;383:685-90).

An experimental study involving inoculation of a panel of inbred mice with the agents causing BSE and variant CJD substantially increased the strength of the scientific evidence for a causal association between variant CJD and BSE (Nature 1997;389:498-501). In this study, groups of inbred mice and a group of cross-bred mice inoculated with brain homogenates from variant CJD cases were reported to have had latency periods and lesion profiles consistent with the BSE pattern.

The latency period, neuropathology, and disease-causing PrP isoforms in transgenic mice expressing bovine PrP that were inoculated with variant CJD, BSE, and scrapie brain extracts provided additional evidence supporting the link between BSE and variant CJD (Proc Natl Acad Sci 1999;96:15137-42).

Has CDC initiated increased surveillance efforts to determine whether the newly recognized variant of CJD occurs in the United States?
Yes. In addition to the ongoing review of national CJD mortality data, CDC has conducted active CJD surveillance in its four established Emerging Infections Program areas (Minnesota, Oregon, Connecticut, and the San Francisco Bay area, California) and in a metropolitan Atlanta site.

Additionally, with the support of the Council of State and Territorial Epidemiologists, CDC conducts follow-up review of clinical and neuropathology records of CJD decedents aged <55 years who are identified through the national mortality data analysis.

CDC, in collaboration with the American Association of Neuropathologists, established the National Prion Disease Pathology Surveillance Center at Case Western Reserve University, Cleveland, Ohio in 1996-1997. This pathology center provides free, state-of-the-art diagnostic services to U.S. physicians. It also helps to monitor the possible occurrence of emerging forms of prion diseases, such as variant CJD, in the United States. For more information about the center visit its website at: http://www.cjdsurveillance.com.

In 2002, CDC reported the occurrence of variant CJD in a 22-year-old Florida resident who was born in and grew up in the United Kingdom. Information about this patient is available at: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5141a3.htm.

Is BSE a foodborne hazard for travelers to Europe?
The current risk for infection with the BSE agent among travelers to Europe is extremely small, if it exists at all. Information describing this risk is available in the document titled "Bovine Spongiform Encephalopathy and Variant Creutzfeldt-Jakob Disease" available on the CDC website at http://www.cdc.gov/ncidod/diseases/cjd/bse_cjd.htm.