Kuru: a critical review

Prion disease: possible implications for oral health care

BACKGROUND

Prion diseases are a group of rare fatal neurodegenerative disorders in humans and animals that are histopathologically characterized by spongiform change within the central nervous system.

TYPES OF STUDIES REVIEWED

The author reviewed all available case reports and any studies of the oral aspects of prion diseases published in peer-reviewed journals and available via PubMed. He then outlined the risk of nosocomial transmission of prions in dental health care.

RESULTS

Sporadic Creutzfeldt-Jakob disease, or sCJD, is the most common of the acquired human prion disorders, and it typically affects elderly people and leads to rapid death. In contrast, variant CJD, or vCJD, has affected young adults from Europe, giving rise to a slow onset disorder comprising both psychiatric and neurological upset. Oral neurological manifestations are rare and seem to occur only in people with vCJD; there are no oral mucosal or gingival manifestations of prion disease. Prions can be detected in the oral tissues--usually the gingivae and dental pulp--of animals experimentally infected with prions. In contrast, prions have not been detected in the pulpal tissue of people with sCJD, and there are no data of pulpal infection in vCJD. There also are no data suggesting that prions are transmitted easily in the dental setting, but there remains the rare risk of such transmission if appropriate infection control measures are not adhered to.

CLINICAL IMPLICATIONS

Few people in the United States and worldwide have prion disease. Oral manifestations are rare. Evidence suggests that the risk of transmission and acquisition of a prion infection as a result of dental treatment is rare, if appropriate infection control measures are maintained.

Prions and the human transmissible spongiform encephalopathies

The last 5 years have seen the emergence of a new disease in humans (vCJD), mainly in the United Kingdom. This emergence has been accompanied by an explosion of scientific data on a novel group of the responsible infectious agents called prions and has profound implications for infection control and transfusion policies. Also of concern is the finding of prions in neural, gingival, pulpal, and salivary tissue in animal models and significant titers of infectivity from extraneural organs (particularly, in cases of vCJD, in lymphoreticular tissues). There is limited information on the presence of prion proteins in the oral tissues from human studies. Because of the differences in patterns of disease in animal models and in strains of prion protein, it is difficult to extrapolate directly these findings to humans, but it illustrates a potential for transmission by way of the dental route. High levels of infectivity may be present in tissues early in the incubation period and before clinical signs and symptoms. The dental profession must turn its attention to the routine decontamination of dental instruments to ensure that these procedures are performed to the highest regulatory standard. Clinicians and manufacturers must work closely together to develop instruments that are either single use or can be presented in a form that can be more easily decontaminated. Clinicians must pay close attention to manufacturers' decontamination instructions and must not reuse items designated as single use, such as endodontic files. Improvements in compliance with these requirements will not only reduce the risk of transmission of TSEs but also other less tenacious infectious agents.

The human transmissible spongiform encephalopathies (TSEs): implications for dental practitioners

Transmissible spongiform encephalopathies (TSEs) are rare, fatal degenerative brain diseases which affect humans and certain animals, and are caused by inheritance or acquisition of prions (PrPs). Inherited TSEs include Fatal Familial Insomnia (FFI), Gerstmann-Straussler-Scheinker syndrome (GSS) and other less well clinically characterised disorders, while the human infective TSEs include sporadic, iatrogenic and variant Creutzfeldt-Jakob disease (vCJD). The causative prions are found especially in neural tissues and spinal fluid, and in the case of vCJD, in lymphoreticular tissue. Available epidemiological evidence suggests that normal social or routine clinical contact with affected patients does not present a risk to health care workers, relatives or the community. Isolation of patients is not considered necessary. Nevertheless as the prions are resistant to conventional chemical, irradiation and heat sterilisation methods, highly specific cross-infection control measures are required for the dental management of patients with, or at notable risk, of TSE. The present article reviews current knowledge of the clinical consequences of prion disease and provides information regarding necessary changes to the cross-infection routine when managing patients infected, or at risk of, prion disease.