Prions The CDC defines transmissible spongiform encephalopathies (TSEs) as a family of rare, progressive neurodegenerative disorders that affect both humans and animals. They are distinguished by long incubation periods and characteristic spongiform changes associated with neuronal loss. The causative agents of TSEs are believed to be prions. The term “prions” refers to “abnormal, pathogenic agents that are transmissible and are able to induce abnormal folding of specific normal cellular proteins called prion proteins that are found most abundantly in the brain” (CDC, 2021c). The functions of normal Identified prion diseases in humans Creutzfeldt-Jakob disease (CJD) is a rapidly progressive, degenerative, neurologic disorder of humans caused by a transmissible prion. The incubation period between exposure and onset of symptoms varies from two years to many decades, though death occurs within one year of the onset of symptoms. Most CJD cases occur sporadically, with no known environmental source, and ten percent are familial. Some iatrogenic transmission has occurred, most notably through corneal transplants (CDC, 2021a). Variant CJD (vCJD) is not the same disease as classic CJD. It has different clinical and pathologic characteristics from classic CJD. Each disease also has a particular genetic profile of the prion protein gene. Variant Creutzfeldt-Jakob disease (vCJD) Severe acute respiratory syndrome (SARS) SARS is a respiratory disease that emerged in China late in 2002 and spread to several countries including Mainland China, Hong Kong, Hanoi, Singapore, and Toronto. There have been cases of laboratory evidence of SARS in the U.S. but no deaths have occurred. SARS outbreaks have occurred in healthcare settings and transmitted to large numbers of healthcare personnel and patients with evidence of droplet, contact transmission, Monkey pox Monkeypox, a rare viral disease found mostly in rainforest countries of Central and West Africa, made a brief appearance in the United States in 2003, and was traced to captive prairie dogs that had been in contact with exotic animals (CDC, 2019a). The disease made another appearance in the United States, and around the world, in 2022 (CDC, 2022b). Monkeypox is caused Norovirus Noroviruses, formerly referred to as Norwalk-like viruses, are members of the Caliciviridae family. Environmental contamination has been documented as a factor in transmission during outbreaks of this highly contagious disease. Widespread, persistent, and undetected contamination of the environment and fomites can make outbreaks extremely difficult to control. Clinical observations and detection of norovirus DNA on surfaces Hemorrhagic fever viruses (HFV) The hemorrhagic fever viruses are a mixed group of viruses that cause serious disease with high fever, skin rash, bleeding diathesis, and high mortality; the disease caused by the viruses is referred to as viral hemorrhagic fever (VHF). Commonly known HFVs are Ebola and Marburg viruses (Filoviridae); Lassa virus (Arenaviridae); Crimean-Congo hemorrhagic fever and Rift Valley fever viruses, or Bunyaviridae; and dengue and yellow fever viruses, or Flaviviridae (CDC, 2019a). Person-to-person transmission is mainly due to direct blood and body fluid contact. Percutaneous exposure to contaminated blood carries a high risk for transmission and increased mortality during the embalming process. Large numbers of Ebola viral
prion proteins are still not completely understood, but the abnormal folding of the prion proteins leads to brain damage and the characteristic signs and symptoms of the disease. Prion diseases are usually rapidly progressive and always fatal. Prion diseases in animals include scrapie in sheep and goats; bovine spongiform encephalopathy (BSE), or “mad cow disease,” in cattle; and chronic wasting disease in deer and elk. BSE, first recognized in the United Kingdom (UK) in 1986, was associated with a major epidemic among cattle that had consumed contaminated meat and bone meal. is a prion disease that was first described in 1996 in the United Kingdom. There is now strong scientific evidence that the agent responsible for the outbreak of prion disease in cows, BSE, is the same agent responsible for the outbreak of vCJD in humans (CDC, 2022c). Although most cases of vCJD have been reported from the UK, cases also have been reported from other parts of Europe, Japan, Canada, and the United States. Healthcare workers use standard precautions when caring for patients with CJD and vCJD. Postmortem handling of these patients will be discussed later in the course. and airborne transmission. The CDC recommends universal precautions, with emphasis on hand hygiene, and contact precautions with emphasis on environmental cleaning, because SARS CoV RNA has been identified on surfaces in the rooms of SARS patients. Airborne precautions, including use of fit- tested NIOSH-approved N95 or higher level respirators, and eye protection are also indicated. by an orthopoxvirus that is similar in appearance to smallpox but causes a milder disease. Transmission from infected animals and humans occurs primarily through direct contact with lesions and respiratory secretions, but airborne transmission from animals to humans, though unlikely, cannot be excluded (CDC, 2019a). five feet above levels normally touched suggest that aerosolized particles may travel distances beyond three feet. Individuals who are responsible for cleaning the environment may be at increased risk of infection. The virus is resistant to many cleaning and disinfection agents and may survive in ten parts per million (ppm or one milligram per liter) or less of chlorine (CDC, 2019a). particles can be found in the skin and the lumina of sweat glands, which indicates that transmission could occur from direct contact with intact skin. Evidence to support direct transmission from intact skin is limited, but postmortem handling of infected bodies is an important risk for transmission. There have been situations where transmission occurred among individuals with no direct contact. In these rare cases, there is speculation that airborne transmission could have occurred. Airborne transmission of HFVs in humans has not been scientifically observed, though the possibility of airborne transmission exists and the CDC has not been able to completely exclude droplet or indirect contact transmission.
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