Human TSEs occur in sporadic, familial, and acquired forms. The most common form, sporadic Creutzfeldt-Jakob disease (CJD), has a worldwide death rate of about 1 case per million people each year, and typically affects people between 55 and 75 years of age. The disease usually begins with a progressive mental deterioration that soon becomes associated with progressive unsteadiness and clumsiness, visual deterioration, muscle twitching (myoclonus), a variety of other neurological symptoms and signs, and is often associated with a characteristic periodic electroencephalogram. The patient is usually mute and immobile in the terminal stages and in most cases, death occurs within a few months of onset of symptoms. TSEs are invariably fatal and there is no proven treatment or prophylaxis.
Similar neurodegenerative diseases also occur naturally in some animal species (scrapie in sheep and goats, chronic wasting disease in deer and elk), or as a result of exposure of susceptible species to infected animal tissues (transmissible mink encephalopathy, bovine spongiform encephalopathy, and spongiform encephalopathy in domestic cats and a variety of captive zoo animals). TSE agents exhibit an unusual resistance to conventional chemical and physical decontamination methods. They are not adequately inactivated by most common disinfectants, or by most tissue fixatives, and some infectivity may persist under standard hospital or healthcare facility autoclaving conditions (e.g. 121°C for 15 minutes). They are also extremely resistant to high doses of ionizing and ultra-violet irradiation and some residual activity has been shown to survive for long periods in the environment. The unconventional nature of these agents, together with the appearance in the United Kingdom, Republic of Ireland and France of a new variant of CJD (vCJD) since the mid- 1990s, has stimulated interest in an updated guidance on safe practices for patient care and infection control.
Diagnosis of Human Transmissible Spongiform Encephalopathies The February 1998 Report of a WHO Consultation the Global Surveillance, Diagnosis and Therapy of Human Transmissible Spongiform Encephalopathies2,3 provides a guideline for diagnostic criteria of human TSEs. Readers should be aware of efforts to revise diagnostic criteria for CJD and vCJD due to the introduction of new diagnostic tests and intense surveillance efforts. Surveillance case definitions (which may not be the same as diagnostic criteria) for both forms of the disease may also be subject to change.
Infection Control Guidelines for Transmissible Spongiform Encephalopathies are provided by the World Health Organization (WHO).
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