Diagnosis and prevention of bovine spongiform encephalopathy and variant Creutzfeldt-Jakob disease

An outbreak of bovine spongiform encephalopathy (BSE) arose in the United Kingdom as a result of prions entering and being recycled through the ruminant food chain. Humans have since developed a variant form of Creutzfeldt-Jakob disease (vCJD), also mostly in the United Kingdom, that occurs in younger individuals and causes prominent psychiatric and/or behavioral manifestations early in disease. Laboratory studies now provide strong evidence that the causative agent of BSE in cattle and vCJD in humans share a common origin. Because of a lack of information regarding the incubation period of vCJD and the number of people who may have been exposed, the future scope of this disease remains unknown. Control of the current and any future outbreaks in cattle requires strict measures to prevent contamination of the animal food chain with prions of any species. Prevention of human exposure mandates the avoidance of neural tissue in all human foods.

Use of containment pans and lids for autoclaving caustic solutions

As a means of decontaminating instruments possibly exposed to Creutzfeldt-Jakob disease, the World Health Organization has recommended immersion and autoclaving in sodium hydroxide. However, this recommendation has raised concerns of possible damage to autoclaves, and hazards to operators as a result of the caustic vapors. A series of experiments has been conducted that demonstrate that there are containment pan-and-lid combinations in which instruments can be autoclaved in sodium hydroxide without risk to the autoclave or the operator.

vCJD screening and its implications for transfusion - strategies for the future?

It remains unclear whether Creutzfeldt Jakob disease (CJD) can be transmitted by blood products. Peripheral blood infectivity is demonstrable in experimental animal transmissible spongiform encephalopathy models and has been transmitted via blood transfusion. However, in man, epidemiological case control, lookback and surveillance studies have failed to demonstrate any evidence of sporadic CJD transmission by blood transfusion. It cannot be assumed that variant CJD is not transmissible in this way because it is a different strain of disease, which is known to involve peripheral lymphoid tissues. There is no immune response to PrP(Sc) (pathogenic isoform of cellular prion protein PrP(C)) and no nucleic acid associated with infectivity has been identified; standard serological and molecular assays are therefore inapplicable. Surrogate markers for cerebral damage are unlikely to be useful for preclinical screening because they reflect the breakdown of the blood-brain barrier in advanced neurological disease. Alpha-haemoglobin stabilizing factor may provide a surrogate marker during the incubation phase. Most approaches to PrP(Sc) discrimination are based on the physicochemical characteristics of PrP(Sc); some are now approaching the specificity and sensitivity required. However, their validation and potential impact on the donor base remain to be resolved.

[The use of disposable instruments of a high performance polymer for tonsillectomy and adenoidectomy]

Cases of the new variant Creutzfeldt-Jakob disease (vCJD) in human beings have to be anticipated in Germany. In subclinical vCJD, the accumulation of prions in lymphoid tissue has been identified prior to their manifestation in cerebral tissue. The remarkable resistance of prions to standard methods of sterilisation questions the safety of reusing metallic surgical instruments. The transmission of vCJD via such reusable surgical instruments in tonsillectomies and adenoidectomies cannot be excluded. In this study, 96 tonsillectomies and adenoidectomies were performed with disposable instruments made of a high performance polymer (Aesculap, Tuttlingen). No increase in the number of intra- or postoperative complications was evident. These disposable instruments may represent an alternative to reusable metallic surgical instruments in potentially infected patients or in patients desiring the use of disposable instruments during their operation for safety reasons.

CJD and the dentist

The last 10 years have seen the emergence of a new disease termed variant CJD. This disease is thought to be initiated by abnormal prion proteins. This article reviews the different clinical manifestations of human prion diseases and provides some background information on the biological nature of this unique infectious agent. Prion proteins present a challenge to infection control because of their relative resistance to the conventional sterilization process. This article highlights the issues involved and discusses current guidelines for management of patients with human transmissible encephalopathies.

Creutzfeldt-Jakob disease: two case studies

Creutzfeldt-Jakob disease (CJD) is a rapidly progressive, neurodegenerative disorder causing dramatic neuromuscular symptoms, profound dementia, and death. In this article, the epidemiology, etiology, modes of transmission, clinical manifestations, determination of possible/probable CJD diagnosis in life, and the postmortem neuropathology of definite CJD are discussed in depth. Case studies of two individuals, each affected by different subtypes of sporadic Creutzfeldt-Jakob disease (sCJD), are presented, along with a discussion of the many challenging nursing and psychosocial issues surrounding the supportive care of these individuals and families in life and death.

Virus-like interference in the latency and prevention of Creutzfeldt-Jakob disease

We previously showed that intracerebral (ic) inoculation of the attenuated SY strain of Creutzfeld-Jakob disease in mice could delay clinical signs and widespread neuropathology evoked by subsequent ic challenge with the more virulent FU strain. Using lower doses of SY and FU ic, we here demonstrate that mice can be protected well into old age without demonstrable neuropathology or pathologic prion protein (PrP-res). In contrast, parallel FU only controls became terminally diseased 1 year earlier. To determine whether factors elaborated in response to SY might be part of this effect, we evaluated brain and serum samples from additional parallel mice at 90 days after SY infection and just before FU challenge. The infectivity of FU preparations was significantly reduced by mixing with these fresh SY brain homogenates but not by mixing with SY serum samples, suggesting that brain cells were elaborating labile inhibitory factors that were part of the protective response. SY infectivity was too low to be detected in these brain homogenates. Although suppression could be overcome by higher FU doses ic, strong protection against maximal doses of FU was observed by using i.v. inoculations. Because myeloid microglia are infectious and also elaborate many factors in response to the foreign Creutzfeld-Jakob disease agent, it is likely that innate immunity underlies the profound protection shown here. In principle, it should be possible to artificially stimulate relevant myeloid pathways to better prevent and/or delay the clinical and pathological sequelae of these infections.

The impact of variant CJD on transfusion practices in the UK

This article describes the chronology of BSE in the UK, and of its transfer as vCJD to humans. The historic and potential future impacts on Transfusion Medicine and Science in the UK--from donor selection to component processing--are summarised, and put in a global setting.

The application of the precautionary principle to the blood system: the Canadian blood system's vCJD donor deferral policy

The precautionary principle is an influential concept that has been widely used in international treaties and declarations involving the protection of the environment. The principle is now being applied to the development of transfusion policy. In this article, we examine the application of the precautionary principle in the policy process leading to Canada's decision to defer donations from individuals who had traveled to the United Kingdom because of concerns over variant Creutzfeldt-Jakob disease. We found that, although the principle prominently influenced the decision-making process, problems existed with its interpretation. In particular, there was difficulty in balancing the risk prevented by applying a precautionary measure against the risk introduced by the same measure; in this case, the potential for shortages of blood. This dilemma is somewhat unique to the public health sector and will likely recur in future applications of the principle to transfusion policy.

Reuse of single use medical devices

During the ten years that I have worked at the Canadian Nurses Protective Society, we have had numerous calls from Operating Room nurses questioning the practice of re-using single use medical devices in their facilities and voicing their concerns about possible harm to patients, themselves and potential liability exposure. Interest in this topic has been rekindled by the recent Saskatchewan case involving the death of a patient from variant Creutzfeld-Jakob Disease (vCJD) and possible transmission of vCJD to 71 patients who may have been exposed to the same endoscope as the deceased while in hospital. In this article, I propose to address some of the concerns related to the reuse of single use medical devices by focusing on the prevalence of this practice, the legal risks involved, regulation of this practice, and risk management.

Pre-clinical diagnosis of transmissible spongiform encephalopathies using rapid tests

During the past few years, important progress has been made in the post-mortem diagnosis of transmissible spongiform encephalopathies (TSEs) (scrapie and BSE) due to the development of the so-called "rapid test" based on the immunological detection of the abnormal form of the prion protein (PrPres) in the central nervous system. These methods now allow routine and high throughput testing, opening the door to large-scale epidemiological studies and systematic testing at slaughterhouses, thus preventing the entry of contaminated carcasses into the human food chain. It has been shown that some of these rapid tests allow pre-clinical diagnosis, anticipating by few months the appearance of clinical signs. In sheep and goat, PrPres can also be detected in peripheral lymphoid tissues a long time before the onset of clinical symptoms. As a consequence, the same rapid tests are suitable for pre-clinical diagnosis of scrapie in these species. It is very likely that the same kind of early diagnosis could be obtained for vCJD. The real challenge in the field of TSE diagnosis is the establishment of a vCJD test, conducted either on blood or urine, since these are the only biological fluids easily accessible from infected people. This is a very important issue to avoid iatrogenic transmission of vCJD within the human population. This is also very difficult because the quantities of infectious agents in the blood are certainly 100-1000 times lower than those present in the brain.

Creutzfeldt-Jakob disease-the perioperative connection

The recent adverse incident at Middlesbrough General Hospital where neurosurgical instruments were used on a patient later diagnosed with sporadic CJD, and then reused on further patients, has major implications for us all as perioperative practitioners. This article looks at what happened and explores what can be done to prevent it in the future.

[Detection of bovine-derived materials in import animal feeds and food by PCR assay]

A PCR assay for detection and identification of bovine--derived materials in import animal feeds and food is developed. A 271 bp sequence from bovine specific mitochondrial DNA is amplified. The amplified specific sequence of the bovine mtDNA from meat and feed samples is demonstrated by both direct sequencing and restriction endonuclease digestion yield analysis. This method can detect bovine mtDNA in those less than 0.125% of bovine meat. Owing that this method is specific, rapid and sensitive, it can be utilized as a routine control assay in prevention of spreading of bovine spongiform encephalopathy in China caused by imported food and animal feeds especially meat and bone meals.

The epidemics of bovine spongiform encephalopathy and variant Creutzfeldt-Jakob disease: current status and future prospects

The large epidemic of bovine spongiform encephalopathy (BSE) in the United Kingdom has been in decline since 1992, but has spread to other countries. The extensive control measures that have been put in place across the European Union and also in Switzerland should have brought the transmission of BSE under control in these countries, provided that the measures were properly enforced. Postmortem tests on brain tissue enable infected animals to be detected during the late stages of the incubation period, but tests that can be performed on live animals (including humans) and that will detect infections early are urgently needed. The number of infected animals currently entering the food chain is probably small, and the controls placed on bovine tissues in the European Union and Switzerland should ensure that any risks to human health are small and diminishing. Vigilance is required in all countries, especially in those in which there has been within-species recycling of ruminant feed. Fewer than 150 people, globally, have been diagnosed with variant Creutzfeldt-Jakob disease (vCJD), but there are many uncertainties about the future course of the epidemic because of the long and variable incubation period. Better control measures are necessary to guard against the possibility of iatrogenic transmission through blood transfusion or contaminated surgical instruments. These measures will required sensitive and specific, diagnostic tests and improved decontamination methods.

A comparison of simulated difficult intubation with multiple-use and single-use bougies in a manikin

In a randomised cross-over study, 20 anaesthetists attempted to place a multiple- or single-use bougie in the trachea of a manikin, in which a grade 3 Cormack and Lehane laryngoscopic view was simulated. The anaesthetists made two attempts at placement with each bougie and were blinded to success (tracheal placement) or failure (oesophageal placement). The success rates for the first attempts with the multiple- and single-use bougies were 85 and 15%, respectively [mean (95% CI) difference between the two bougies 70% (40-84%); p < 0.001]. The success rates for the second attempts were similar to those for the first attempts with both bougies. There is an increased risk of failure to intubate the trachea when using a single-use bougie, and this must be weighed against the unquantified risk of cross-infection from prions when using a multiple-use bougie.

Cling film as a barrier against CJD in corneal contact A-scan ultrasonography

PURPOSE

To determine the validity of covering a corneal contact transducer probe with cling film as protection against the transmission of Creutzfeldt-Jakob disease (CJD).

METHODS

The anterior chamber depth, lens thickness and vitreous chamber depth of the right eyes of 10 subjects was recorded, under cycloplegia, with and without cling film covering over the transducer probe of a Storz Omega Compu-scan Biometric Ruler. Measurements were repeated on two occasions.

RESULTS

Cling film covering did not influence bias or repeatability. Although the 95% limits of agreement between measurements made with and without cling film covering tended to exceed the intrasessional repeatability, they did not exceed the intersessional repeatability of measurements taken without cling film.

CONCLUSIONS

The results support the use of cling film as a disposable covering for corneal contact A-scan ultrasonography to avoid the risk of spreading CJD from one subject to another.

[Method on PCR detection of bovine materials in animal feedstuffs]

The reliable, simple and easy to operate methods were established to extract DNA from animal feedstuffs. A set of PCR primers were designed for bovine specific mitochondrial DNA sequence. With this method, PCR can be successfully utilized to evaluate the presence of bovine materials in animal feedstuffs. A set of commonly used primers of 18Sr-RNA were designed as endogenuous reference gene, and check on the quality of template extraction from animal feedstuffs, and avoid the result of false negative. PCR amplification condition was one cycle of 96 degrees C for 2 min, then 35 cycle of (94 degrees C for 40s, 60 degrees C for 50s, 72 degrees C for 60s), and finally one cycle of 72 degrees C for 5 min. PCR amplified specific gene sequence 271 bp for bovine materials from animal feedstuffs.

IC of CJD in the OR

Review precautions for the safe handling of surgical materials that may be contaminated with infectious agents from patients with Creutzfeldt-Jakob disease.

Impact of 'Mad Cow Disease' publicity on trends in meat and total vitamin A consumption in Geneva between 1993 and 2000

BACKGROUND

In March 1996, revelations about the possible risk for humans of the 'mad cow disease' epidemic had a sudden impact on the diets of European populations.

OBJECTIVE

To assess changes in meat and nutrient intakes in adults living in Geneva, Switzerland from 1993 to 2000.

DESIGN

Independent annual cross-sectional surveys (4047 women and 4092 men total).

MAIN OUTCOME MEASURE

Dietary habits assessed and compared to baseline (January 1993-April 1996) via validated semi-quantitative food-frequency questionnaire.

RESULTS

Women beef abstainers increased from 8.9 to 14.9% in late 1996 (P<0.001) and 13.3% in 1997 (P<0.05); among meat consumers, in late 1996 meat/beef intakes declined -10/-12% (both P<0.05). From 1997 to 2000 most intake levels drifted back toward those at baseline, but chicken intakes were significantly (all P<0.05) greater each year (+19% in 2000 (P<0.001). Consistent but less dramatic changes were observed among men. From late 1996 until 2000, liver abstention was significantly (all P<0.05) greater (women from 60 to 78%; men from 61 to 73% in 2000; (both P<0.001). The only nutrient intakes that decreased significantly (all P<0.05) each year from 1997 through 2000 were retinol and total vitamin A women: -22% (P<0.001); -11% (P<0.05) respectively; men: -16% (P<0.001); -10% (P<0.05) respectively, in 2000). Total vitamin A intakes exceeded the dietary reference intake (DRI) for liver eaters (women 185%, men 153%), but were below the DRI for liver abstainers (women 83%; men 66%) in 2000.

CONCLUSION

The decreases in beef and liver consumption since late 1996 led to the discovery of a long-term disparity in the retinol and total vitamin A intakes of liver eaters vs abstainers.

[Hygenic measures for Creutzfeldt-Jakob disease]

The Creutzfeldt-Jakob disease (CJD) belongs to the so-called prion diseases or transmissible spongiform encephalopathies. The iatrogenic transmission of the pathogen by direct contact with infectious tissue, tissue extracts and surgical instruments has been demonstrated. CJD is not an infectious disease in the usual sense. Transmission is not possible by normal social contact nor by nursing measures just as CJD can not be transferred by normal skin contact or contact with blood, serum or other patient' secretions. Therefore, CJD patients do not have to be isolated, because strict conformity to the generally recognized rules of hygiene is completely sufficient. The high resistance of prions to environmental influences requires the combination of different disinfection and sterilization measures before inactivation of the pathogen occurs and it is possible to exclude transmission by medical products.

Public confidence in medical technology

Three headlines have appeared in the British press recently, all of which concern health-care issues related to technology, and which have profound implications for public confidence in medical practice. Once again, at the year's end, it is necessary to reassess our own procedures and safeguards to prevent erosion of public confidence in our industry.

Variant Creutzfeldt-Jakob disease: an unfolding epidemic of misfolded proteins

Variant Creutzfeldt-Jakob disease (vCJD) is an emerging infectious disease believed to be the human manifestation of bovine spongiform encephalopathy (BSE). Variant CJD belongs to a family of human and animal diseases called transmissible spongiform encephalopathies (TSE). The pathogenesis of TSE is not fully understood, but a modified form of a normal cellular protein plays a central role. Current measures to control vCJD aim to prevent transmission of the infectious agent from animals to humans through food or pharmaceutical products and to prevent transmission from person to person via medical interventions. The anticipated development of preclinical diagnostic tests and treatments for vCJD will create new control options and difficult choices.

Measuring prions causing bovine spongiform encephalopathy or chronic wasting disease by immunoassays and transgenic mice

There is increasing concern over the extent to which bovine spongiform encephalopathy (BSE) prions have been transmitted to humans, as a result of the rising number of variant Creutzfeldt-Jakob disease (vCJD) cases. Toward preventing new transmissions, diagnostic tests for prions in livestock have been developed using the conformation-dependent immunoassay (CDI), which simultaneously measures specific antibody binding to denatured and native forms of the prion protein (PrP). We employed high-affinity recombinant antibody fragments (recFab) reacting with residues 95-105 of bovine (Bo) PrP for detection and another recFab that recognizes residues 132-156 for capture in the CDI. We report that the CDI is capable of measuring the disease-causing PrP isoform (PrP(Sc)) in bovine brainstems with a sensitivity similar to that of end-point titrations in transgenic (Tg) mice expressing BoPrP. Prion titers were approximately 10(7) ID(50) units per gram of bovine brainstem when measured in Tg(BoPrP) mice, a figure approximately 10 times greater than that determined by bioassay in cattle and approximately 10,000x greater than in wild-type mice. We also report substantial differences in BoPrP(Sc) levels in different areas of the obex region, where neuropathology has been consistently observed in cattle with BSE. The CDI was able to discriminate between PrP(Sc) from BSE-infected cattle and Tg(BoPrP) mice as well as from chronic wasting disease (CWD)-infected deer and elk. Our findings argue that applying the CDI to livestock should considerably reduce human exposure to animal prions.

Factors governing speed of societal responses to threats: precision of definition of the threat may be more important than its anticipated likely severity

Responses to two recent international public health threats, AIDS and BSE, both exemplify missed opportunities for early intervention. They are in contrast to the response to the Y2K computer issue, a threat of lesser-anticipated consequence but one that was more precisely defined. Lessons from these experiences should inform the public health response to new threats, such as the emergence of multiple drug resistance in human pathogens.

Studies on the removal of a bovine spongiform encephalopathy-derived agent by processes used in the manufacture of human immunoglobulin

BACKGROUND AND OBJECTIVES

There is still uncertainty over how the agent of variant Creutzfeld-Jakob disease (vCJD) would partition during the manufacture of plasma derivatives. In this study, a BSE-derived agent was used as a vCJD model to determine the extent to which infectivity could be removed by selected steps used in the manufacture of intravenous immunoglobulin (IVIG).

MATERIALS AND METHODS

Murine-passaged BSE (strain 301V), in the form of a microsomal fraction prepared from infected brain, was used to "spike" the starting material in three experiments. The partitioning of BSE infectivity was measured over Fraction I+III precipitation, borosilicate microfibre depth filtration and Seitz depth filtration, with these steps being examined individually and in series.

RESULTS

Most 301V infectivity partitioned into Fraction I+III (log reduction 2.1). Infectivity remaining in Supernatant I+III was reduced by AP20 glass-fibre depth filtration (log reduction 0.6) and subsequently removed to below the limit of detection by Seitz KS80 depth filtration, giving an overall log reduction of > or = 2.9 for the three steps in series. By contrast, glass-fibre depth filtration gave a log reduction of 2.4 when challenged directly with "spiked" feedstock. Seitz KS80 depth filtration gave a log reduction of > or = 3.1 when challenged directly with 'spiked' feedstock and also removed residual infectivity to below the limit of detection when applied as the final step in series.

CONCLUSIONS

Results using a BSE-derived agent suggest that vCJD infectivity should be substantially removed from immunoglobulin G (IgG) solutions by Fraction I+III precipitation and Seitz KS80 depth filtration. The three different process steps examined acted in a complementary manner to one another when operated in series. However, the data demonstrated that it would be inappropriate to add together the reduction factors that had been derived for each step in isolation.

Managing the risk of nosocomial transmission of prion diseases

PURPOSE OF REVIEW

Prion diseases such as Creutzfeldt-Jakob disease represent a unique infection control problem because prions exhibit an unusual resistance to conventional chemical and physical decontamination methods. This paper reviews the recent literature and provides recommendations for the prevention of nosocomial transmission of prion agents.

RECENT FINDINGS

Recommendations to prevent the cross-transmission of infection from medical devices potentially contaminated with prions have been based primarily on prion inactivation studies. Newer recommendations consider inactivation data, but also use epidemiological studies of prion transmission, the infectivity of human tissues, and the efficacy of removing microbes by cleaning. Prion-specific disinfection/sterilization is required in only limited settings. Healthcare workers are not at risk of acquiring transmissible spongiform encephalopathies. Blood or blood products have not been demonstrated to be vehicles for transmission.

SUMMARY

On the basis of scientific data, only critical (e.g. surgical instruments) and semicritical devices contaminated with high-risk tissue (i.e. brain, spinal cord, eye) from high-risk patients (e.g. with known or suspected Creutzfeldt-Jakob disease) require special treatment.

Variant Creutzfeldt-Jakob disease--a problem for general dental practitioners?

Over a hundred deaths from variant Creutzfeldt-Jakob disease (vCJD) have now been recorded. The incubation period for vCJD may be up to 40 years and the number of asymptomatic carriers in the population could be as many as 100,000. Confirmed iatrogenic transmission of other human transmissible spongiform encephalopathies raises the possibility of cross-infection from apparently healthy persons who are incubating vCJD. Decontamination techniques routinely used in general dental practice are incapable of inactivating the infective protein responsible for transmitting the disease. So far, no evidence exists to preclude the risk of iatrogenic infection occurring during dental procedures. The author reviews present knowledge of the infective agent, its transmissibility, its origins, current guidelines and the implications for dental practice.