Jorge E Delgado-Hachmeister, MC, (1) M Siegfried Rangel-Frausto, MC, (2) Samuel Ponce de León, MC (3). 
Delgado-Hachmeister
JE, Rangel-Frausto MS Delgado-Hachmeister , Ponce de León S.
transmissible spongiform encephalopathies. Mex
Public Health 2002, 44:69-75.
The full text of this article is available at: http://www.insp.mx/salud/index.html
Abstract Transmissible spongiform encephalopathies (TSEs) have gained great importance in recent years. By the appearance of bovine spongiform encephalopathy (BSE) and new variant Creutzfeldt-Jakob Ermedàs (nvCJD), the latter likely to be acquired by eating beef contaminated. To date, reported 109 cases of nvCJD in humans and the great majority of them occurring in the United Kingdom. No one knows the actual size which may take the TSE in humans, however some think that we are at the beginning of a pandemic nvCJD. In this paper we discuss several aspects of TSEs and methods for preventing the transmission of these diseases in both ruminants and humans. The full text of this article is available at: http://www.insp.mx/salud/index.html
Keywords: transmissible spongiform encephalopathies, bovine spongiform encephalopathy, Creutzfeldt-Jakob disease, infection hospitalaria
Delgado-Hachmeister JE,
Rangel-Frausto MS, Ponce de León S.
Transmissible spongiform encephalopathies.
Salud Publica Mex 2002;44:69-75.
The English version of this paper is available at: http://www.insp.mx/salud/index.html
Abstract
Transmissible spongiform encephalopathies (TSE) are a group of diseases which have received a lot of attention in recent years. The interest on these diseases has been stimulated by the appearance of bovine spongiform encephalopathy (BSE) and the new variant of Creutzfeldt-Jakob disease (nvCJD); the latter is likely to be acquired by ingesting contaminated beef. Until now 109 cases of nvCJD have been reported, most of them occurring in the United Kingdom. Some experts think That this is the Beginning of a nvCJD pandemic. Deep Knowledge of the common mechanisms of transmission of TSE is Needed to Prevent the Emergence of a pandemic in humans.We address TSE Various Aspects of TSE and discuss prevention Methods of TSE in ruminants and humans. The Inglés version of this paper is available at: / / www.insp.mx / health / index.html
Key words: transmissible spongiform encephalopathies, encephalopathy, bovine spongiform; Creutzfeldt-Jakob disease; cross
Infection transmissible spongiform encephalopathies ( TSEs) or prion diseases are a group of neurological conditions closely related to histopathological characteristics, occurring in humans and animals. TSE hereditary mechanisms are developed, sporadic or infectious. In recent years the prion diseases have generated much interest, especially the epidemic of bovine spongiform encephalopathy (BSE) and the emergence of new variant Creutzfeldt-Jakob disease (nvCJD), the latter apparently related to the food intake from cows with EEB.1, 2
prion-related diseases in animals
The TSE of sheep and goats (scrapie) is the prototypic prion-related disease. This has been known for over 250 years ago as an enzootic disease. In the United Kingdom from 0.5 to 1% of the sheep have this condition each year.
BSE was discovered in 1985 in the UK, and has evolved from an epidemic estimated that up to one million cows were infected with BSE in this area. Have also documented several cases of BSE in other European countries, although limited, and so far with a dimension less than that seen in the UK, but cases are increasing year by year. Only 1 January to 6 August 2001 have reported 87 cases of BSE in Germany, and in the same period are reported as 52 in España.3 These data are worrisome, as in previous years the occurrence of cases BSE in other European countries did not occur or was a rare phenomenon. In the Americas, including Mexico, have not reported indigenous cases of EEB.3
The origin of BSE probably comes from cattle feed manufactured from ruminants (sheep and cattle) with TSE, mostly meat and flour hueso.4, 5 Since the United Kingdom of TSE in sheep and goats is endemic, it was hypothesized that sheep contaminated waste were the initial source of BSE. However, it also is assumed that BSE prions originated spontaneously in cattle, so that the disease was amplified by the recycling of waste from cows.
Although not reported BSE cases in Mexico, it is necessary to maintain an epidemiological alert to prevent an epidemic similar to that seen in Europe.
Clinical diagnosis of this disease in cattle is suspected by the appearance of various symptoms and signs. Symptoms are: apprehension, fear, or depression often gaze. Symbols are distinguished tenderness or hyperreflexia, muscle twitching, tremor and myoclonus, gait ataxia, including hypermetria, and autonomic dysfunction such as decreased rumination, bradycardia and heart rhythm alterado.3 In the case of suspected BSE should make a detailed study of the brain and brain stem after the death of the animal as quickly as possible.
To prevent the emergence of this disease in Mexico, it is important to conduct surveillance histopathological studies in ruminants with neurological disease, impose restrictions on the import of live species of ruminants and their products, designing a policy for the importation of embryos; and the prohibition of food fortification with corpses of the same genus (ruminants to ruminants.) When reporting cases of BSE should not penalize farmers, but to provide compensation to them, in order to reduce the registration and to prevent diseased animals from entering the human food chain.
prion-related diseases in humans
prion-related diseases in humans are unique in biology, and etiology with sporadic, genetic or infectious. Have described several variants of prion diseases in humans, including Kuru, Creutzfeldt-Jakob Disease (CJD) family, sporadic CJD, iatrogenic CJD and new variant CJD, Gerstmann-Sträussler-Scheinker syndrome, fatal insomnia fatal familial insomnia espontáneo.6
Most cases of prion diseases occur spontaneously, as in the case of sporadic CJD (sCJD) which occurs in a person in a million inhabitants. The distribution of sCJD is equal for men and women. The etiology of sCJD is not known, it is postulated that somatic mutation is a gene of PrP (prion protein), it occurs as a rare stochastic phenomenon, the protein PrPc change to PrPsc. There is a common and benign polymorphism at codon 129 of PrP gene coding for methionine or valine. Homozygous for methionine at this position have a higher risk for developing sporadic CJD or iatrogénica.7
There are three hypotheses about the nature of the infectious agent of TSEs. The first postulates that these diseases are caused by a protein replica themselves misma.8 The second states that the agent is a virus pequeño.9 The third says that it is a plus ribavirin. A ribavirin is a small molecule (possibly a nucleic acid) associated with a host protein, perhaps PrP.10 far has the most credibility is the hypothesis of the disease protein. This was reinforced with the awarding of Nobel Prize to Stanley Prusiner in 1997.11 It is the first time that this award is offered a job yet entirely hypothetical and not proven. We briefly discuss the hypothesis of protein. According to this hypothesis, prions are transmissible particles that have no nucleic acids and are composed exclusively of a modified protein PrPsc. The normal cellular PrPc is converted into PrP Sc through a posttranslational processing, by which PrP acquires a high-helices
b.11-13 Although the human prion diseases can be transmitted an experimental basis, the acquired forms until recently had been confined to unusual situations. For example, kuru was spread by ritual cannibalism in Papua New Guinea.14 Other cases of human illness related to acquired prions have resulted from iatrogenic transmission of CJD.
This transmission has occurred during the corneal transplantation, graft placement dura mater, the administration of cadaveric human growth hormone, implantation of intracranial EEG electrodes contaminated surgeries (especially neurosurgery and ophthalmic surgery) where they used surgical instruments and apparatus contaminados.15
The new variant was introduced in 1994 in Britain, for the first time, cases of CJD in teenagers and young adults, and eventually received the name of new variant CJD (nvCJD) .16 Until then it was extremely rare cases of CJD are present in young people and also features histopathological findings were unusual, he had presence of amyloid plaques formed with PrP (prion protein) surrounded by a halo of intense spongiform degeneration. The emergence of cases of nvCJD in a restricted geographical area (mainly UK), which occurs simultaneously in the BSE epidemic, has suggested that BSE crossed the species barrier and was transmitted to humans through contaminated beef.
Until August 6, 2001 have been reported in the United Kingdom 106 definite or probable cases of nvCJD. Notes that in 2000 final 28 cases were diagnosed, which represents the highest number reported since 1995, and the general trend since the beginning of the epidemic in the UK, shows that year after year more cases of nvECJ.17 In France, two patients were diagnosed with nvCJD and Ireland one.
Epidemiological studies have identified different dietary habits in the subjects concerned and do not know why nvCJD affects mainly adolescents and young adults. I really do not know if we are in the beginning of an epidemic of prion-related disease in humans, similar to what happened with kuru or BSE. Some estimate that hundreds of thousands of people will develop nvCJD, while others postulate that cases of nvCJD will be few, similar to what happened with CJD iatrogénica.18, 19
We suggest that you take all precautions necesarias, incluyendo las que discutimos en este artículo, para prevenir el desarrollo de casos de EEB y de la nvECJ en México. El no adoptar las precauciones que discutimos puede ser una difícil lección en años venideros.
La nvECJ se caracteriza por el desarrollo de un trastorno neuropsiquiátrico progresivo que se manifiesta por la aparición de ataxia, demencia, mioclonía o corea, sin el patrón típico electroencefalográfico (EEG) de la ECJe. Por otro lado, como ya mencionamos, existe un patrón histopatológico distinto. Por lo tanto, para poder confirmar un caso de la nvECJ se requiere efectuar un estudio histopatológico cerebral.
En el cuadro I enumeramos los criterios diagnostics for nvCJD.
Guidelines for the prevention of transmission of TSEs in the hospital
The following guidelines are based, almost entirely, in a document published by the global organization
government.20 Whereas TSE can be iatrogenically acquired strategies are designed to prevent transmission. Some of these recommendations are impractical at times. However, the medical personnel who are involved in the management of patients with TSE should follow as far as possible. TSE No patient should be denied any means, because if you follow the recommendations proposed risk transmission to other patients or health workers is minimal.
TSE agents are unusually resistant to chemical and physical methods of decontamination. They are not inactivated by most disinfectants, or tissue fixatives, as well as some residual infectivity may persist under conditions of standard autoclave (eg 121 ° C for 15 minutes.) They are extremely resistant to high doses of ionizing radiation and ultraviolet. On the other hand, has shown that TSE agents can survive for long in the environment. Iatrogenic transmission
TSEs are not transmitted from person to person, but theoretically this can occur during the practice of invasive medical procedures. To prevent transmission of TSE patients to other individuals (patients and healthcare workers) should be stratified to different risk categories. This risk depends on three considerations: 1. The probability that an individual develops a TSE, 2. The degree of infectivity of tissues or fluids of these patients, 3. The nature and route of exposure to these tissues.
Patients at highest risk are those with a diagnosis or suspicion of TSE. The information available indicates that tissues with the highest infectivity are the central nervous system (brain, spinal cord and eye). Low infectivity tissues are represented by the cerebrospinal fluid and various other bodies outside the CNS (lung, liver, kidney, spleen / lymph nodes and placenta). The tissues in which infectivity has never been detected include the heart, skeletal muscle, peripheral nerves, adipose tissue, gingival tissue, intestine, adrenal glands, thyroid, prostate, testis and body secretions (urine, feces, saliva, mucus, semen, milk, tears, sweat and serous).
When calculating the risk we must also consider the route of exposure. Exposure of intact skin and mucous membranes, except of the eye, involves almost no risk, however, it is prudent to avoid this type of contact, especially when working with high infectivity tissues. Transdermal exposures, including exposure of non-intact skin and mucous membranes, eyes and splashes into the wounds inflicted by sharp instruments (eg needles) imposed a greater potential risk. Avoid this type of exposure when working with tissues high or low infectivity. SNC exposure (eg inoculation of the eye or CNS) with any infectious material represents a very serious risk and should be implemented whenever necessary precautions to avoid such exposure.
Care
patient
normal social contact and non-invasive diagnostic procedures pose no risk to health workers, relatives or community. TSE patients should not be isolated, may be in private rooms will not only adhere to recommended standard precautions. However, because the TSE progressing rapidly, the patient will soon develop dependence so that the allocation of a special nurse in a private room is recommended for humanitarian reasons.
patient excreta must be handled in accordance with local laws. No special precautions are required for cutlery, and suction feeding tubes, and sheets. Dental procedures
There is epidemiological evidence indicating that dental procedures are associated with the acquisition of an iatrogenic TSE. However, animal studies indicate that gingival tissue and dental pulp are potentially infectious. And so it is recommended to use extra caution in patients with TSE when performing procedures involving neurovascular tissue (eg root canal). In dental procedures, which does not work with neurovascular tissue, the usual preventive methods are sufficient. Precautions include using disposable instruments, incinerate contaminated dental equipment decontamination tissue or neurovascular an effective method to remove TSE agents (see below) and set the procedures at the end of the day to properly clean
instrumentos.20
Diagnostic Procedures Patients with TSE, as well as other patients, they practice some type of diagnostic procedures including ophthalmoscopy, endoscopy, colonoscopy, urinary catheters or vascular and pulmonary function tests or cardiaca.20
In this type of procedure should not take any special precautions. But it is suggested diagnostic interventions planned for later in the day, so that the instruments are cleaned more thoroughly. However, when the instruments are exposed to high or low tissue infectivity (see above), they must submit to a sterilization process that can tolerar20 more intense (see below). Transfusion
Different countries have designed policies to reduce the risk of TSE transmission through blood products. Theoretically can be transmitted by blood TSE, even apparently healthy patients but found in the incubation phase of the disease. Experimental studies indicate that transmission of TSEs in sheep to sheep, during the asymptomatic phase of the disease, can through transfusions sanguíneas.21
In the U.S. donor policy excludes people who were in the United Kingdom for a cumulative time less than six months, from 1980 until 1996.22 Other countries have adopted this measure, among which include Canada, Australia, New Zealand, Switzerland, Japan and Germany. This practice should also apply in our country until there is enough evidence to rule out the possibility of TSE transmission by transfusion of blood products. Surgical procedures
When a patient with suspected or confirmed TSE, scheduled for surgery, go to the hospital, the division responsible for monitoring of hospital infections should be informed. Then very carefully planned by a multidisciplinary team (surgeon, sterilization, hospital epidemiologist, infectious disease, etc.) the procedure and the handling, storage, cleaning, decontamination and disposal of instruments used during surgery so that the intervention was done in an operating room, involving a compact personal computer surgical team used a single use (surgical gowns, gloves, masks, mask, surgical drapes) check all the equipment is reusable, is maintained flow instruments in a single line, are incinerated all waste and surgical instruments (when possible) mark all specimens as infectious biological waste, and clean all surfaces in accordance with recommendations establecidas20 (see below).
handling surgical instruments
methods for decontamination of surgical instruments are described below. The method is determined by the degree of infectivity of tissues and the way in which instruments are to be subsequently reused. If surgical utensils coming into contact with high infectivity tissues are recommended for single use instruments. In the event that are not available for single use instruments, it is best to destroy these reusable instruments.
Although the cerebrospinal fluid is classified as low infectivity tissue is recommended that the instruments were in contact with it are managed in the same manner as if it were contaminated instruments with high infectivity tissues. Of course this applies to instruments used for lumbar puncture.
Surgical instruments used in fabrics of high or low infectivity, should be placed in a sturdy container and leak-proof, which is labeled "infectious biological waste." This instrument should be transferred to the sterilization department and be sterilized by a method effective (see below), or be transferred to the incinerator. This must happen quickly and Quarantine
eficiente.20
If suspected diagnosis of a TSE, if the instruments can be stored in a safe place, they can be sterilized with the best possible way and save in rigid containers, to confirm or discard the diagnosis of TSE. Decontamination procedures
TSE agents are unusually resistant to sterilization and disinfection methods traditional. The variability in the effectiveness of decontamination methods is influenced by the nature and physical state of the tissues infected. We know, for example, that the infectivity is stabilized by fixing methods such as alcohol, formalin or glutaraldehyde or dry surfaces. Therefore, contaminated materials should not be exposed to substances fixing and should be kept immersed in disinfectant chemicals from being used until they are disinfected.
The surest way to decrease the potential for residual infectivity from surgical instruments to be cremated. However, this is not possible with all the surgical equipment. In this case you must use the most effective decontamination process that can tolerate the instrument (see below).
When possible should be combining two effective disinfection methods for the instrument. The procedures that use heat and NaOH (either simultaneously or consecutively) seem to be most effective.
Some expensive instruments, such as fiber optic endoscopes, are not subjected to decontamination procedures as intense. These can be protected by wrapping them in such a way as to minimize exposure to contaminated surfaces.
Decontamination methods for transmissible spongiform encephalopathies
The most effective method in reducing the risk of residual infectivity is the destruction of the instruments by incineration. Where possible, instruments and other materials subject to reuse, should be kept moist from the time of exposure to decontamination. If that can be done in a safe, you should remove particles attached to instruments, by means of a mechanical type cleaning. The following recommendations
lists recommended disinfection methods, in order of effectiveness. These recommendations are based on the report of the World Health Organization. New methods may emerge as more scientific evidence accumulates.
1. Incineration
• Use for all instruments, materials and disposable trash
• Method of choice for all instruments exposed to high infectivity tissues.
2. Autoclave / chemical methods for instruments resistant to heat
• Immerse in sodium hydroxide (NaOH) and heated in an autoclave of gravity displacement at 121 º C for 30 minutes, clean, wash in water and subjected to sterilization methods routine
• Immerse in NaOH or sodium hypochlorite for one hour, transfer instruments to water heated in an autoclave of gravity displacement at 121 º C for one hour, clean and submit to sterilization routine
• Immerse in NaOH or sodium hypochlorite for an hour, wash in water and then transferred to an open container and heat in an autoclave of gravity displacement (121 ° C) or porous load (134 º C) for an hour, clean and submit to sterilization routine
• Immerse in NaOH and boil for 10 minutes atmospheric pressure, clean, wash in water and subjected to routine sterilization
• Immerse in sodium hypochlorite (preferred) or NaOH (alternative) at room temperature for an hour, clean, wash in water and subjected to routine sterilization
• Autoclave at 134 º C for 18 minutes.
3. Chemical methods for surfaces and heat sensitive instruments
• Wash with NaOH (2N) or undiluted bleach and soak for an hour, remove and rinse with water
• If surfaces can not tolerate exposure to NaOH or hypochlorite, washing removes the vast majority of the infectivity by dilution, plus you'll get more disinfection by washing with a partially effective method. Conclusions
European BSE epidemic is a concern, year after year reported more cases of BSE in several European countries. This information suggests that there may be a similar phenomenon occurred in the United Kingdom in other countries: a large-scale epidemic of BSE and finally the occurrence of nvCJD cases of interspecies transmission of prions by contaminated meat from cattle to humans. To date we do not know what will be the magnitude of nvCJD, but there may be thousands of cases present the same in coming years. In countries of the Americas, including Mexico, there have been reports of BSE, however it is extremely important that we establish the necessary measures to prevent the emergence of this disease in our cattle, they should include, but are not limited to the prohibition of importation of live species, their products and ruminant embryos of most, if not all, European countries and the ban on enrichment food with corpses of the same gender. Failure to follow these recommendations can be a difficult lesson for our livestock industry and ultimately for many Mexicans who could develop nvCJD. The emergence of TSEs in humans, also requires that all health workers know the mechanisms of transmission, clinical picture and the necessary steps to be followed to prevent nosocomial transmission of TSEs. While the number of reported cases of nvCJD is limited, there is the possibility that it is a disease of great magnitude with features of great concern: it affects young people, producing degeneration of the central nervous system is progresiva, rápidamente mortal y no existe tratamiento disponible.
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