Information from the Centers for Disease Control and Prevention

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 2002, 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 Web site of the Office International Des Epizooties.

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?

To prevent BSE from entering the United States, severe restrictions were placed on the importation of live ruminants and certain ruminant products from countries where BSE was known to exist. These restrictions were later extended to include importation of ruminants and certain ruminant products from all European countries, Japan, and Israel.

However, in March 2006 the third confirmed case of the disease in the U.S. was confirmed. The meat was believed never to have entered the food supply.

Is BSE a foodborne hazard in the United States?

It is unlikely that BSE would be a foodborne hazard in this country. Because the use of ruminant tissue in ruminant feed was probably a necessary factor responsible for the BSE outbreak in the United Kingdom and because of the current evidence for possible transmission of BSE to humans, the U.S. Food and Drug Administration instituted a ruminant feed ban in June 1997 that became fully effective as of October 1997.

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 national Creutzfeldt-Jakob disease (CJD) surveillance.

The Centers for Disease Control and Prevention 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. A summary of these data was published in the Journal of the American Medical Association on Nov. 8, 2000.

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 people under 30 in the United States remain extremely rare (less than 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 the 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 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 during April and May 1996.

In 1996, with the support of the Council of State and Territorial Epidemiologists, CDC initiated an ongoing follow-up review of clinical and neuropathology records of CJD decedents under 55 who are identified through the national mortality data analysis.

Also in 1996, CDC, in collaboration with the American Association of Neuropathologists, established the National Prion Disease Pathology Surveillance Center at Case Western Reserve University, Cleveland, Ohio. 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.

Source: Centers for Disease Control and Prevention