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Samenvatting Essential Microbiology for Dentistry
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Samenvatting van Essential Microbiology for Dentistry voor de cyclus 1.3 en 1.4
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Essential Microbiology for DenistryPrions and prion diseases
Prions are unique elements in nature, and they are agents of a group of chronic diseases
called prion diseases or transmissible spongiform encephalopathies. They infect essentially
the nerve tissues of animals and humans, and manifest with long incubation periods lasting
up to decades.
The relevance of this chronic disease to denistry relates tot he realization (1) that the
infectious agenst is extremely difficult to destroy and (2) of the probalility of infection
transmission in clinical settings.
The major features of prions are given below:
They are neither viruses nor viriods
Prions do not have either DNA or RNA
The native form of the prion protein, a nomal constituent of healthy neural tissues, is
designated whereas the disease-related isoform derived from the latter is
designated.
The abnormal form, is derived from the native precursus by a post-translational
process leading to a conformatinal change from an a-helical structure to an insouble
B-sheet structure.
The abnomral form resists destruction and accumulates in the neural tissues, causing
vacuolation of cells, leading to a sponge-like appearance
They have the ability to self- replicate but with a very long incubatoin period
The prototype prion agent caused scrapie, a central nervouw system disease in sheep
As the organism is highly resistent to heat, chemical agents and irradiation, either
special autoclaving procedures are required to sterilize contaminated instruments or
disposable instruments/materials have to be used for surgical procedures on infected
patients
The prion agent can be transmitted to cows, mink, cats and mice, for instance, when
fed with infected material
Iatrogenic transmission of prion disease by neurosurgical instruments has been
reported
Major prion-induced diseases or transmissible spongiform encephalopathies
Kuru
Kuru is the fatal neurological disease first descriped in societies in Papua New Guinea who
consumed human brain. It is no longer prevalent owing to the cessation of this practise.
Creutzfeldt-Jakob disease
Is a globally prevalent, rare, chronic encephalopath: 10% of cases are familial and carry the
mutated prion gene; the remainder are either acquired or sporadic. Onset is in middle to
late life (40-60 years); the clinical course lasts course lasts fora bout 7-18 months.
Variant Creutzfeldt- Jakob disease
Localized to Europe, especially the UK; it almost always affect teenagers or young adults. The
disease is spread by consumption of prion-infected animal tissues.
, Pathogenenis
Prions appear to replicate incessantly, first in lymphoid tissue, and then in brain cells where
they produce intracellular vacuoles and depostion of altered host prion protein. These
vacuoles give rise to the sponge-like appearance of the brain on microscopic examination.
The disease is uniformly fatal.
Transmission
Kuru is transmitted in infected human brain by cannibalism. Other modes of CJD
transmission are mostly unknown. There are a few reports of iatrogenic transmission by
medical and surgical procedures; hereditary acquisition occurs in familial cases;
contaminated food is thought to cause acquired disease.
Prevention and dental implications
There is no treatment for or vaccine against prion-induced disease
Hence the only preventive measure is not consuming suspect food
The level of infectivity in oral and dental tissues is uncertain, although in one in vitro
study of the dental pulp of eight patient, no prion particles vould be detected
A few retrospective studies indicate no evidence of dental procedures
increasingtransmission risk, and published iatrogenic transmission studies show no
evidence of associated dental procedures.
Hoofdstuk 36 Principles of infection control
Cross infection
Principles of infection transmission
Transmission of infection from one person to another requires:
1. A source of infection: the person with the infection is callesd the index case.
2. A mode or vehicle by which the infective agent is transmitted, for example: blood,
droplets of saliva, instruments contaminated with blood, saliva and tissue debris.
3. A route of transmission, for example: inhalation, ingestion.
Vaccination and drug therapy are used to protect health care workers in the practice from
the infected source patient.
Source of infection
The sources of infection in clinical dentistry are mainly human; they include:
1. People with overt infections who liberate large numbers or organisms into the
environment (bijv wounds). In routine clinical denistry, few patients with acute life-
threatening diseases are seen. Common infections circulating in the community can
be transmitted in the dental environment from patients or staff with overt infections
such as herpes.
2. People in the prodromal stage of certain infections. During the prodrome (an early
symptom indicating the onset of a disease or illness) or the incubationg period, the
organisms multiply without evidence of infection; although patients are healthy at
this stage, they are highly infectious. The requirement for occupational vaccination of
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