Abstract
Prion diseases are sub-acute neurodegenerative diseases that affect humans and some domestic and free-ranging animals. Infectious prion agents are considered to comprise solely of abnormally folded isoforms of the cellular prion protein known as PrPSc. Pathology during prion disease is restricted to the central nervous system where it causes extensive neurodegeneration and ultimately leads to the death of the host. The first half of this review provides a thorough account of our understanding of the various ways in which PrPSc prions may spread between individuals within a population, both horizontally and vertically. Many natural prion diseases are acquired peripherally, such as by oral exposure, lesions to skin or mucous membranes, and possibly also via the nasal cavity. Following peripheral exposure, some prions accumulate to high levels within the secondary lymphoid organs as they make their journey from the site of infection to the brain, a process termed neuroinvasion. The replication of PrPSc prions within secondary lymphoid organs is important for their efficient spread to the brain. The second half of this review describes the key tissues, cells and molecules which are involved in the propagation of PrPSc prions from peripheral sites of exposure (such as the lumen of the intestine) to the brain. This section also considers how additional factors such as inflammation and aging might influence prion disease susceptibility.
Highlights
The prion diseases are a unique group of sub-acute neurodegenerative diseases that affect humans and certain domestic and free-ranging animals
The pathology caused during prion disease is considered to be restricted almost entirely to the central nervous system (CNS), where it causes extensive neurodegeneration which leads to death
To reduce the risk of potential transmission of variant Creutzfeldt-Jakob disease (CJD) by blood transfusion the UK implemented universal leucodepletion in 1999. This rationale was based on observations that PrPSc could be detected in lymphoid tissues of vCJD patients [66,67] implying that cells such as lymphocytes might potentially contaminate the blood-stream with prions
Summary
The prion diseases are a unique group of sub-acute neurodegenerative diseases that affect humans and certain domestic and free-ranging animals. The characteristic histopathological features of CNS prion diseases include vacuolation in the brain (spongiform pathology), neurodegeneraton, microgliosis, astrocytosis, and abnormal accumulations of PrPSc. Several different forms of prion diseases have been described: spontaneous, genetic, or acquired through various routes of exposure (Table 1). Examples of vertical prion transmission between an infected mother to the developing fetus or offspring have been reported In addition to their important health and economic impacts to livestock industries, some prion disease have zoonotic potential. Sporadic CJD (sCJD), in contrast, typically affects elderly individuals and has an unknown etiology and incidence of approximately 1/million population per annum throughout the world Whether this prion disease is acquired is uncertain, but a study using experimental mice has proposed that sheep scrapie prions may have zoonotic potential and cause a disease in the recipients with characteristics identical to sCJD [3]. This section describes how additional factors such as inflammation and aging can influence prion disease susceptibility
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