Prion Diseases as Transmissible Zoonotic Diseases

Prion diseases, also called transmissible spongiform encephalopathies (TSEs), lead to neurological dysfunction in animals and are fatal. Infectious prion proteins are causative agents of many mammalian TSEs, including scrapie (in sheep), chronic wasting disease (in deer and elk), bovine spongiform encephalopathy (BSE; in cattle), and Creutzfeldt–Jakob disease (CJD; in humans). BSE, better known as mad cow disease, is among the many recently discovered zoonotic diseases. BSE cases were first reported in the United Kingdom in 1986. Variant CJD (vCJD) is a disease that was first detected in 1996, which affects humans and is linked to the BSE epidemic in cattle. vCJD is presumed to be caused by consumption of contaminated meat and other food products derived from affected cattle. The BSE epidemic peaked in 1992 and decreased thereafter; this decline is continuing sharply owing to intensive surveillance and screening programs in the Western world. However, there are still new outbreaks and/or progression of prion diseases, including atypical BSE, and iatrogenic CJD and vCJD via organ transplantation and blood transfusion. This paper summarizes studies on prions, particularly on prion molecular mechanisms, BSE, vCJD, and diagnostic procedures. Risk perception and communication policies of the European Union for the prevention of prion diseases are also addressed to provide recommendations for appropriate government policies in Korea.     

Update: Creutzfeldt-Jakob disease associated with cadaveric dura mater grafts--Japan, 1978-2008

Creutzfeldt-Jakob disease (CJD) is the most common of the human prion diseases (also known as transmissible spongiform encephalopathies), which, according to the leading hypothesis, are caused by an abnormal protein (i.e., prion) that is able to induce abnormal folding of normal cellular prion proteins. Annual worldwide incidence of these always fatal neurodegenerative diseases is estimated at 0.5-2.0 cases per million population. CJD can occur sporadically, or as a genetic disease, or can be transmitted iatrogenically. In 1996, a new human prion disease, variant CJD (vCJD), was first described in the United Kingdom. This disease was believed to have resulted from human consumption of cattle products contaminated with the prions responsible for bovine spongiform encephalopathy (BSE, commonly known as mad cow disease). That year, in part to check for possible vCJD cases, a national survey was conducted in Japan; 821 CJD cases were identified, including 43 cases associated with receipt of cadaveric dura mater grafts. A single brand of dural graft (Lyodura) produced by a German manufacturer before May 1987 was identified as the most likely vehicle of transmission in all but one case. By 2003, continued surveillance in Japan had identified a total of 97 such cases. Since then, an additional 35 cases have been identified. This report updates previous reports and summarizes the investigation of all 132 cases to date linked to dural grafts. The results suggest that, because of the long incubation period between graft receipt and symptom onset (possibly >24.8 years), continued surveillance in Japan might identify additional CJD cases associated with dural grafts.     

Schutz vor BSE

By the mid 1980s, bovine spongiform encephalopathy (BSE) emerged in the United Kingdom (UK) and reached its peak in the early 1990s with up to 37,000 cases. In the year 2000, BSE was diagnosed for the first time for a cow born in Germany. Since then, 413 cases of BSE have been detected. About 10 years after the first BSE cases were detected, variant Creutzfeldt–Jakob disease (vCJD), a new variant of Creutzfeldt–Jakob disease (CJD), was described in the UK. Legal measures for protection from BSE are described. The number of cases of vCJD and the development of the BSE situation in Germany and Bavaria until 2009 are presented.     

Bovine Spongiform Encephalopathy: "Mad Cow Disease"

Bovine spongiform encephalopathy (BSE), also known as "mad cow disease," is a fatal brain disease of cattle first recognized in the United Kingdom. In humans, the most common transmissible spongiform encephalopathy is Creutzfeldt-Jacob Disease (CJD). Although no cases of CJD have been directly linked to beef consumption, an advisory committee has reported that 10 recent cases of a CJD variant may be associated with BSE. This announcement has alarmed consumers well beyond the borders of the United Kingdom.     

The risk of accidental transmission of transmissible spongiform encephalopathy: identification of emerging issues

The transmissible spongiform encephalopathies (TSEs), thought to be caused by prions, are fatal neurodegenerative disorders of humans and animals. Despite their rarity, human prion diseases have received prominence because the consumption of prion-contaminated meat from cattle with bovine spongiform encephalopathy (BSE) is thought to be responsible for the emergence of variant Creutzfeldt-Jakob disease (vCJD) in humans. Clinical criteria for the diagnosis of vCJD is now available. Recent, more startling evidence suggests that the clinical presentation of vCJD may vary and that patients may present as classical (sporadic) CJD or may have subclinical infection and be apparently healthy. These patients may still pose a risk of iatrogenic transmission through surgical or medical (blood transfusion) procedures. The aim of future work is to develop preclinical screening tests for the identification of infected but still healthy individuals. The future course of vCJD is still uncertain. Modelling studies to predict the cases of vCJD depend on the date of origin of BSE and time of infection, which is, at best, only approximated. As the number of cases of BSE in the UK declines, the risk of BSE in other countries from imported cattle or meat and bone meal from the UK has been increasing. It is also recognized that other animal species (farmed, domestic and wild animals) other than cows are susceptible to TSEs. The possibility of interspecies transmission of TSEs and the global presence of the disease suggests a need for a co-ordinated worldwide risk management approach to eradicate TSEs.     

Creutzfeldt-Jakob disease not related to a common venue--New Jersey, 1995-2004

Beginning in June 2003, the New Jersey Department of Health and Senior Services (NJDHSS) and CDC were notified of a suspected cluster of deaths caused by Creutzfeldt-Jakob disease (CJD) in persons reportedly linked to Garden State Racetrack in Cherry Hill, New Jersey. Concerns were raised that these deaths might have resulted from consumption of meat contaminated with the agent causing bovine spongiform encephalopathy (BSE, commonly called "mad cow disease") served at racetrack restaurants during 1988-1992. Consumption of BSE-contaminated cattle products has been linked to a new variant form of CJD (vCJD) in humans. This report summarizes the results of an investigation that determined the deaths were not linked causally to a common source of infection. The findings underscore the need for physicians to arrange for brain autopsies of all patients with clinically suspected or diagnosed CJD.     

Bovine spongiform encephalopathy in a dairy cow--Washington state, 2003

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.     

BSE safety standards: An evaluation of public health policies of Japan, Europe, and USA

Since the advent of bovine spongiform encephalopathy (BSE) in the United Kingdom in 1986, new BSE cases have recently become rare. However, in Japan and the United States, positive cases have started to be seen recently. The rise in BSE cases paved the way for the human form of this disease, the variant Creutzfeldt-Jakob disease (vCJD). The observed trends in the UK may be attributed to effective implementation of public health policies coupled with increased vigilance through advancement in science and technology, or they may well be a reflection of the natural disease progression. We aim to discuss the BSE chronology of events, and compare examination methods, costs and cost-efficiency, management, and public policies of Japan, Europe, and the USA.     

The emergence of bovine spongiform encephalopathy and related diseases.

Since 1986, approximately 170,000 cases of bovine spongiform encephalopathy (BSE) have occurred among approximately one million animals infected by contaminated feed in the United Kingdom. A ruminant feed ban in 1988 resulted in the rapid decline of the epidemic. Transmissible spongiform encephalopathies due to agents indistinguishable from BSE have appeared in small numbers of exotic zoo animals; a small outbreak among domestic cats is declining. Creutzfeldt-Jakob disease (CJD) has been intensively monitored since 1990 because of the risk BSE could pose to public health. In 1995, two adolescents in the United Kingdom died of CJD, and through the early part of 1996, other relatively young people had cases of what became known as new variant CJD, whose transmissible agent (indistinguishable from that of BSE) is responsible for 26 cases in the United Kingdom and one in France. Areas of concern include how many cases will appear in the future and whether or not use of human blood and blood products may cause a second cycle of human infections.     

Public health service recommendations for the use of vaccines manufactured with bovine-derived materials

The Center for Biologics Evaluation and Research (CBER), U.S. Food and Drug Administration (FDA) learned earlier this year that some vaccines were manufactured with bovine-derived materials obtained from countries in which bovine spongiform encephalopathy (BSE) or a substantial risk for BSE exists. A list of these countries is published by the U.S. Department of Agriculture (USDA). This information was of concern because cases of variant Creutzfeldt-Jakob disease (vCJD) have been attributed to, among other possibilities, eating beef products from cattle infected with the agent of BSE. No evidence exists that cases of vCJD are related to the use of vaccines, and no cases of vCJD have been reported in the United States.     

Transmissible spongiform encephalopathies in Australia.

The Australian National Creutzfeldt-Jakob Disease Registry (ANCJDR) commenced surveillance in September 1993 as part of the Commonwealth's response to 4 cases of pituitary hormone (gonadotrophin)-associated Creutzfeldt-Jakob disease (CJD). With the passage of time, the Registry has become responsible for ascertaining all human transmissible spongiform encephalopathies (TSE; also known as prion diseases) within Australia since 1970. Included in the spectrum of diseases monitored are classical (sporadic, genetic, and health care acquired) CJD, and variant CJD (vCJD), first reported in 1996 in the United Kingdom. Variant CJD has not yet been diagnosed in Australia. Final classification of persons with suspected human prion disease is based upon all available clinical, investigational and pathological information. Ascertainment methods are diverse and include prompted, half-yearly personal communications from neurologists and neuropathologists, death certificate searches, and morbidity separation coding searches of major hospital, and State and Territory databases. More recently, referral for diagnostic CSF 14-3-3 protein testing (performed by the ANCJDR) has considerably increased prospective notifications of suspect cases. As at September 2001 there were 460 cases on the register; 237 definite cases, 168 probable and 55 incomplete cases awaiting final classification.     

Comments on present-day spread and epidemiology of BSE and prion diseases

Prion diseases of animals and man are neurological diseases with amyloidal deposition of the respective proteins. As to prion disease, the cellular prion protein is in its abnormal isoform(s) an essential component of prion protein aggregates found in affected tissue. In contrast to all neurodegenerative diseases like Morbus Alzheimer or Huntington's disease, prion diseases are transmissible. Therefore, prion diseases were designated Transmissible Spongiform Encephalopathies (TSE). The diseases have been well known for decades. Scrapie was first described around 1750, a BSE case was reported in the 1850-ties most likely a misdiagnosis, and in 1920/1930 the human Creutzfeldt-Jakob disease (CJD) had been described. Transmission of CJD i. e. Kuru had been suspected in the early 1950 s and was erroneously classified as slow virus disease. The CJD transmission posed a problem to humans when transplants from CJD cases were used for treatment. Fortunately, these iatrogenic transmissions remained limited. But with the advent of BSE and appearance of variant CJD cases in the UK and some places in Europe scientists suspected that transmission from cattle to man could have happened. From animal models we know of successful transmission via several routes. Species barriers do not completely prevent transmission. Rather, transmission barriers might exist controlling individual susceptibility against prions. Modes of transmission, susceptibility to transmission, identification of receptor molecules as well as molecular mechanisms of the transmission process are being investigated with great intensity. Current knowledge leads us to assume that inapparent stages of prion infection wrongly suggest a (non-existent) species barrier. This inapparent infection precedes overt disease, and, hence, most research focuses on the development of highly sensitive assay systems for detection of minute amounts of pathological prion protein in suspected cases. Inapparence also should warn us to underestimate BSE or human vCJD cases; at present, approx. 145 cases occurred in Europe and one probable case in Hong Kong (June 2003). Whether BSE had spread to other parts of the world by animal nutrition components or meat can neither be excluded nor confirmed at this time. New data on transmission and consequences of BSE for the human population are summarised in this review.     

On the question of sporadic or atypical bovine spongiform encephalopathy and Creutzfeldt-Jakob disease

Strategies to investigate the possible existence of sporadic bovine spongiform encephalopathy (BSE) require systematic testing programs to identify cases in countries considered to have little or no risk of orally acquired disease or to detect a stable occurrence of atypical cases in countries in which orally acquired disease is disappearing. To achieve 95% statistical confidence that the prevalence for sporadic BSE is no greater than 1 per million (i.e., the annual incidence of sporadic Creutzfeldt-Jakob disease [CJD] in humans) would require negative tests in 3 million randomly selected older cattle. A link between BSE and sporadic CJD has been suggested on the basis of laboratory studies but is unsupported by epidemiologic observation. Such a link might yet be established by the discovery of a specific molecular marker or of particular combinations of trends over time of typical and atypical BSE and various subtypes of sporadic CJD, as their numbers are influenced by a continuation of current public health measures that exclude high-risk bovine tissues from the animal and human food chains.     

Bovine spongiform encephalopathy and food safety

The governments of Great Britain and France disagree on the safety of British beef with respect to bovine spongiform encephalopathy (BSE). Eventually the consumer might have the burden to decide whether beef from Britain is safe to eat with regard to the new variant of Creutzfeldt-Jakob disease (vCJD). Outside Britain the incidence of BSE increases. Probably in continental Europe, the use of high risk material, derived from non-British cattle in the subclinical stage of BSE, poses a greater threat than beef imported from Great Britain. The risk to contract vCJD depends on two unknown factors: the susceptibility of man to BSE and the amount of success in keeping infectious tissue of BSE-incubating cattle out of the human food chain. Until the susceptibility of humans to BSE and the extent to which our food is contaminated become known, no clear-cut advice can be given on the safety of certain food items. There appears to be a genetic predisposition to vCJD, i.e. methionine homozygosity at codon 129 of the normal human prion protein gene. The European Community should ban the use of any high risk material for production of food, except in production processes for which inactivation of the BSE agent has been proven. The facts that are known at this moment allow the conclusion that gelatin and beef products of unknown origin and composition pose a greater health threat than eating genuine beef (muscle tissue).     

Risk of variant Creutzfeldt-Jakob disease in France

BACKGROUND: France has the second highest number of variant Creutzfeldt-Jakob disease (vCJD) cases worldwide. Imports of bovine carcasses from the UK probably constituted the main source of exposure of the French population to the bovine spongiform encephalopathy (BSE) agent. Meat products consumed whilst visiting the UK have also been considered as a possible source of exposure. METHODS: We estimated the number of future vCJD cases in France using a simulation approach. Both the distribution of the vCJD incubation period and the age-dependent susceptibility to the BSE agent were estimated from UK data. The French epidemic was simulated by gender and birth-cohort from data on the infectivity of UK bovine tissues and simulations of the French consumption of infected beef products. We also used data on travel to the UK between 1980 and 1995. RESULTS: We predicted 33 future cases of vCJD: 12 in the 1940-69 birth-cohort and 21 in the post-1969 birth-cohort. No case was predicted in the pre-1940 cohort. Based on our model, simulated vCJD cases occurred later in the older (1940-69) than in the younger cohort (post-1969). Age at onset was stable in the post-1969 cohort and increased in the older cohort. The model predicted a small excess of male patients. No case was attributed to travels in the UK. CONCLUSIONS: This modelling confirms that a large vCJD epidemic in France is very unlikely. Since France (where 60% of the total British exports of bovine carcasses were exported) has been highly exposed to the BSE agent, our results are reassuring for most countries worldwide.     

Source of variant Creutzfeldt-Jakob disease outside United Kingdom

We studied the occurrence of variant Creutzfeldt-Jakob disease (vCJD) outside the United Kingdom in relation to the incidence of indigenous bovine spongiform encephalopathy (BSE) and to the level of live bovines and bovine products imported from the UK during the 1980s and the first half of the 1990s. Our study provides evidence that a country's number of vCJD cases correlates with the number of live bovines it imported from the UK from 1980 to 1990 (Spearman rank correlation coefficient [r(s)] 0.73, 95% confidence interval [CI] 0.42-0.89, p < 0.001). Similar correlations were observed with the number of indigenous BSE cases (r(s) 0.70, 95% CI 0.37-0.87, p = 0.001) and carcass meat imported from the UK from 1980 to 1996 (r(s) 0.75, 95% CI 0.45-0.89; p < 0.001) Bovine imports from the UK may have been an important source of human exposure to BSE and may have contributed to the global risk for disease.     

Die variante Creutzfeldt-Jakob-Krankheit (vCJK)

In the wake of the bovine spongiform encephalopathy (BSE) epidemic, variant Creutzfeldt-Jakob disease (vCJD) has emerged as a previously unknown prion disease of humans. The initial occurrence of vCJD was observed in 1995/1996, and, so far, a total of 219 vCJD cases have been reported worldwide from seven European and four non-European countries. Of these, 172 cases were observed in the United Kingdom. The exact prevalence of sub- or pre-clinical vCJD infections is unclear. Despite effective measures that have been implemented against both BSE in ruminants and its transmission to humans, there is now a theoretical risk of secondary vCJD transmissions from human to human, for example via blood and blood products, organs and tissues, or contaminated surgical instruments and medical devices. Four cases of probable vCJD transmissions via blood have been described, as well as one case of secondary infection via a plasma product. This article provides an overview of the surveillance and epidemiology of vCJD and outlines public health strategies for the risk assessment and risk management of this novel BSE-associated prion disease in humans.     

Bovine spongiform encephalopathy in the United Kingdom: memorandum from a WHO meeting.

This Memorandum reviews the current state of research being carried out on transmissible spongiform encephalopathies (TSE) and examines the results of epidemiological studies conducted on bovine spongiform encephalopathy (BSE) and Creutzfeldt-Jakob disease (CJD) in the United Kingdom. It is concluded that the BSE epidemic is on the decline and the policies adopted in the United Kingdom are sufficient to minimize the risk of exposure to BSE of all species, including humans.     

Predicting incidence of variant Creutzfeldt-Jakob disease from UK dietary exposure to bovine spongiform encephalopathy for the 1940 to 1969 and post-1969 birth cohorts

BACKGROUND: To investigate variant Creutzfeldt-Jakob disease (vCJD) incubation period, transmission barrier, and short-term vCJD predictions for methionine homozygotes in 1940-1969 and post-1969 birth cohorts by use of gender- and age-specific exposure intensities to bovine spongiform encephalopathy (BSE), based on consumption of beef mechanically recovered meat (MRM) and head meat. METHODS: Simulation (from vCJD infections generated randomly from gender and age-specific dietary exposure intensities to BSE), constrained to equal the 47 and 64 vCJD onsets before 2001 in 1940-1969 and post-1969 birth cohorts, was used to estimate lognormal (and other) incubation mean and standard deviation which fitted the calendar year distribution of observed vCJD onsets; and to explore exponential decay in susceptibility to infection with age above 15 years. RESULTS: For the post-1969 birth cohort, the best-fitting lognormal incubation period mean of 11 years (SD 1.5 years and 195 infections) was associated with 194 vCJD onsets (64 before 2001, 105 in 2001-2005, and 25 in 2006-2010). About one-fifth of simulated vCJD onsets before 2001 arose from infections in 1990-1996; age and gender of simulated and observed vCJD patients agreed closely. For the 1940-1969 birth cohort, well-fitting lognormal means ranged widely, the marginally best fitting being 26 years (SD 16.5 years and 382 infections; 47 vCJD onsets before 2001, 58 in 2001-2005, and 63 in 2006-2010). An age-dependent susceptibility function was required to match the age distribution of vCJD patients in the 1940-1969 birth cohort. CONCLUSIONS: About three-fifths of predicted vCJD onsets are expected to be in males, and nearly two-thirds of vCJD onsets in 2001-2005 are expected to be in post-1969 birth cohort according to best-fitting predictions.     

Probable variant Creutzfeldt-Jakob disease in a U.S. resident--Florida, 2002

On April 18, 2002, the Florida Department of Health and CDC announced the occurrence of a likely case of variant Creutzfeldt-Jakob disease (vCJD) in a Florida resident aged 22 years. This report documents the investigation of this case and underscores the importance of physicians increasing their suspicion for vCJD in patients presenting with clinical features described in this report who have spent time in areas in which bovine spongiform encephalopathy (BSE) is endemic.