Prions are infectious proteins causing fatal, transmissible neurodegenerative diseases of animals and humans. Replication involves template-directed refolding of host encoded prion protein, PrPC, by its infectious conformation, PrPSc. Following its discovery in captive Colorado deer in 1967, uncontrollable contagious transmission of chronic wasting disease (CWD) led to an expanded geographic range in increasing numbers of free-ranging and captive North American (NA) cervids. Some five decades later, detection of PrPSc in free-ranging Norwegian (NO) reindeer and moose marked the first indication of CWD in Europe. To assess the properties of these emergent NO prions and compare them with NA CWD we used transgenic (Tg) and gene targeted (Gt) mice expressing PrP with glutamine (Q) or glutamate (E) at residue 226, a variation in wild type cervid PrP which influences prion strain selection in NA deer and elk. Transmissions of NO moose and reindeer prions to Tg and Gt mice recapitulated the characteristic features of CWD in natural hosts, revealing novel prion strains with disease kinetics, neuropathological profiles, and capacities to infect lymphoid tissues and cultured cells that were distinct from those causing NA CWD. In support of strain variation, PrPSc conformers comprising emergent NO moose and reindeer CWD were subject to selective effects imposed by variation at residue 226 that were different from those controlling established NA CWD. Transmission of particular NO moose CWD prions in mice expressing E at 226 resulted in selection of a kinetically optimized conformer, subsequent transmission of which revealed properties consistent with NA CWD. These findings illustrate the potential for adaptive selection of strain conformers with improved fitness during propagation of unstable NO prions. Their potential for contagious transmission has implications for risk analyses and management of emergent European CWD. Finally, we found that Gt mice expressing physiologically controlled PrP levels recapitulated the lymphotropic properties of naturally occurring CWD strains resulting in improved susceptibilities to emergent NO reindeer prions compared with over-expressing Tg counterparts. These findings underscore the refined advantages of Gt models for exploring the mechanisms and impacts of strain selection in peripheral compartments during natural prion transmission.

PURPOSE: Extended use of N95 respirator masks is far more prevalent during the coronavirus disease 2019 (COVID-19) pandemic. As WOC nurses, we were tasked with formulating procedures for protecting the facial skin integrity of healthcare workers (HCWs) using personal protective devices when caring for patients with suspected or active COVID-19, while avoiding contamination when the masks are donned or doffed. This quality improvement project describes how we approached this project within the limited time frame available as we cared for patients with established and suspected COVID-19. PARTICIPANTS AND SETTING: This project focused on HCW use of N95 respirator masks and dressings currently available in our facility. The 4 WOC nurses acted as quality improvement project directors and as participants. The setting for our project was our facility's simulation laboratory. APPROACH: We evaluated 6 topical products (an alcohol-free liquid acrylate, thin film dressing, thin hydrocolloid dressing, hydrocolloid blister care cushion, thin foam transfer dressing, and thick foam dressing) applied to skin in contact with 3 N95 respirators; all are available on our facility's formulary and all are in widespread clinical use. After the product was applied to the face and nose, the N95 respirator was donned and evaluated for fit. Participants then wore the devices for 10 hours and doffed the mask using established facility procedures. In order to evaluate for potential contamination including possible aerosolization, we applied a commercially available fluorescent lotion to simulate the presence of infectious particles. Contamination was assessed using an ultraviolet light for all dressings except for the alcohol-free liquid acrylate. We also evaluated cutaneous responses (skin integrity, irritation, comfort) during this period. OUTCOMES: We found that contamination of the simulated pathogen did not occur with removal of any of the protective products. No skin irritation was noted with any of the tested products after a 10-hour wear time underneath the N95 respirator masks, but mild discomfort was experienced with 3 of the dressings (thin film dressing and both hydrocolloid dressings). CONCLUSION: Based on these experiences, we recommend application of an alcohol-free liquid acrylate film to prevent facial skin injury associated with friction from the extended use of an N95 respirator mask. We further recommend performing a fit test and user-performed seal check with the use of any topical dressing and especially those that add cushion. For the duration of the COVID-19 pandemic, we recommend use of protective dressings to maintain skin integrity and protection from coronavirus infection as HCWs continue to provide care to all of patients under their care.

No abstract

The regularly repeating periodic nucleosome organization is clearly resolved in the chromatin of the isolated salivary chromosomes of Drosophila melanogaster. A new microsurgical procedure of isolation in buffer A of Hewish and Burgoyne (1973, Biochem. Biophys. Res. Commun., 52:504-510) yielded native Drosophila salivary chromosomes. These chromosomes were then swollen and spread by a modified Miller procedure, stained or shadowed, and examined in the electron microscope. Individual nucleoprotein fibers were resolved with regularly repeated nucleosomes of ~10 nm diameter. Micrococcal nuclease digestion of isolated salivary nuclei gave a family of DNA fragments characteristic of nucleosomes for total chromatin, 5S gene, and simple satellite (p = 1.688 g/cm 3) sequences.The repeating periodic nucleosome structure has now been clearly demonstrated in the chromatin of a wide variety of organisms ranging from viruses, yeast, protozoa, and insects to vertebrates (1-3). These demonstrations cover interphase nuclei of tissues varying through early embryonic, fiver, thymus, kidney, erythrocytes, ovaries, and testes (4-6), as well as mitotic chromosomes (7). However, there has been a paucity of demonstrations of nucleosomes in what are probably the most extensively studied of all animal chromosomes, viz., the salivary chromosomes of Drosophila melanogaster. The only pubfished micrographs employed nuclei rather than cytogenetically mappable spread chromosomes and a sweRing procedure which included 2 M urea in conjunction with the detergent Joy (3). There are a number of reasons for this. First, the Miller technique usually takes as its starting material whole nuclei in free suspension rather than spread chromosomes on a surface. Secondly, classically spread salivary chromosomes have been acid-fLxed, which very likely induces transitions in uhrastructure. Thirdly, the nuclear membrane of salivary gland cells is particularly difficult to lyse without damage to the chromosomes. We can now readily resolve the nucleosome repeat unit in spread Drosophila salivary chromosomes. Our demonstration was made possible by a new isolation procedure yielding native Drosophila salivary chromosomes which has been developed in our laboratory (8).Over the past years we have been developing a microsurgical procedure for isolation of these structures simply in the physiological saline of D'Angelo (9). Physical stabilization of the 262 structures was achieved by the inclusion of 0.05% formaldehyde (8). Very recently, it has become possible to isolate them in the buffer A of Hewish and Burgoyne (10), the solvent in which early nuclease digestion experiments gave the first evidence of a 200 base pair (bp) repeating module in chromatin. In this solvent the physical stability of chromatin is enhanced by the polycations, spermine, and spermidine, which give rise to physical but not covalent cross-linking.We have also investigated the organization of Drosophila salivary polytene chromatin by micrococcal nuclease digestion.The resulting DNA ...