Structural Studies of the Corneal Stroma

The corneal stroma is an unusual connective tissue in that it is transparent to visible light and that it can swell to many times its original weight when placed in salt solution with a consequent loss in transparency with swelling. The stroma consists of lamellae of parallel collagen fibrils, of uniform diameter, embedded in a ground substance. It also contains glycosaminoglycans which are negatively charged at physiological pH. The organisation of the collagen fibrils and their relationship to the glycosaminoglycans are important when considering both the transparency and the ability to swell of the fresh tissue and the reason for the loss in transparency on swelling. Experiments were undertaken to study changes in the stroma which take place on swelling as a function of the pH and~he ionic strength of the bathing solution. Initially, the total water content per unit dry weight is studied as a function of the bathing solution and the time of dwelling. Low-angle x-ray diffraction techniques are used to monitor the centre-to-centre distance between the collagen fibrils (the interfilament spacing) as a function of hydration as well as the reflections due to the packing of the tropocollagen molecules from which the fibrils are formed. Thirdly, the fixed charge concentration due to the polyelectrolytes in the stroma is calculated from microelectrode measurements of the potential difference which exists between the stroma and the bathing solution. Fourthly; the absorbance of the stroma to visible light is measured as a function of hydration in various solutions. The results of these four different techniques indicate the importance of the fixed charge on the corneal macromolecules. This fixed charge must give rise to an unequal distribution of permeant ions between the stroma and the bathing solution which leads to a Donnan, osmotic, pressure. This Donnan pressure appears to be the main cause of swelling. Measurement of the fixed charge from the potential difference which also arises from the unequal distribution of permeant ions, shows similar behaviour with pH and ionic strength to that estimated from the swelling results. This dependence is also similar to the behaviour expected from polyelectrolyte gel theory. The value of the interfilament spacing, for a given hydration, is shown to depend on the pH of the bathing solution so that more fluid goes into the lattice of fibrils with some solutions that with others. The water not going into the lattice may be in the form of 'lakes' as suggested by Benedek (1971). The reflections from the packing of tropocollagen molecules along the fibrils are unusual in that, although they index on a repeat of around 66nm, the first order reflection is absent. The Patterson function from such a x-ray pattern is calculated and compared with that from scleral collagen which shows the first order reflections. Finally, the transmission of light by the stroma is shown to decrease linearly with increasing hydration, the rate of decrease being dependent on the pH of the bathing solution. Correlations between the rate of loss of transmission and the rate of swelling as well as between the percentage water in 'lakes' with the transmission of the stroma are discussed

Impact of fatigue as the primary determinant of functional limitations among patients with post-COVID-19 syndrome: a cross-sectional observational study

OBJECTIVES: To describe self-reported characteristics and symptoms of treatment-seeking patients with post-COVID-19 syndrome (PCS). To assess the impact of symptoms on health-related quality of life (HRQoL) and patients' ability to work and undertake activities of daily living. DESIGN: Cross-sectional single-arm service evaluation of real-time user data. SETTING: 31 post-COVID-19 clinics in the UK. PARTICIPANTS: 3754 adults diagnosed with PCS in primary or secondary care deemed suitable for rehabilitation. INTERVENTION: Patients using the Living With Covid Recovery digital health intervention registered between 30 November 2020 and 23 March 2022. PRIMARY AND SECONDARY OUTCOME MEASURES: The primary outcome was the baseline Work and Social Adjustment Scale (WSAS). WSAS measures the functional limitations of the patient; scores of ≥20 indicate moderately severe limitations. Other symptoms explored included fatigue (Functional Assessment of Chronic Illness Therapy-Fatigue), depression (Patient Health Questionnaire-Eight Item Depression Scale), anxiety (Generalised Anxiety Disorder Scale, Seven-Item), breathlessness (Medical Research Council Dyspnoea Scale and Dyspnoea-12), cognitive impairment (Perceived Deficits Questionnaire, Five-Item Version) and HRQoL (EQ-5D). Symptoms and demographic characteristics associated with more severe functional limitations were identified using logistic regression analysis. RESULTS: 3541 (94%) patients were of working age (18-65); mean age (SD) 48 (12) years; 1282 (71%) were female and 89% were white. 51% reported losing ≥1 days from work in the previous 4 weeks; 20% reported being unable to work at all. Mean WSAS score at baseline was 21 (SD 10) with 53% scoring ≥20. Factors associated with WSAS scores of ≥20 were high levels of fatigue, depression and cognitive impairment. Fatigue was found to be the main symptom contributing to a high WSAS score. CONCLUSION: A high proportion of this PCS treatment-seeking population was of working age with over half reporting moderately severe or worse functional limitation. There were substantial impacts on ability to work and activities of daily living in people with PCS. Clinical care and rehabilitation should address the management of fatigue as the dominant symptom explaining variation in functionality

SARS-CoV-2 Omicron is an immune escape variant with an altered cell entry pathway

Vaccines based on the spike protein of SARS-CoV-2 are a cornerstone of the public health response to COVID-19. The emergence of hypermutated, increasingly transmissible variants of concern (VOCs) threaten this strategy. Omicron (B.1.1.529), the fifth VOC to be described, harbours multiple amino acid mutations in spike, half of which lie within the receptor-binding domain. Here we demonstrate substantial evasion of neutralization by Omicron BA.1 and BA.2 variants in vitro using sera from individuals vaccinated with ChAdOx1, BNT162b2 and mRNA-1273. These data were mirrored by a substantial reduction in real-world vaccine effectiveness that was partially restored by booster vaccination. The Omicron variants BA.1 and BA.2 did not induce cell syncytia in vitro and favoured a TMPRSS2-independent endosomal entry pathway, these phenotypes mapping to distinct regions of the spike protein. Impaired cell fusion was determined by the receptor-binding domain, while endosomal entry mapped to the S2 domain. Such marked changes in antigenicity and replicative biology may underlie the rapid global spread and altered pathogenicity of the Omicron variant

The evolving SARS-CoV-2 epidemic in Africa: Insights from rapidly expanding genomic surveillance

INTRODUCTION Investment in Africa over the past year with regard to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing has led to a massive increase in the number of sequences, which, to date, exceeds 100,000 sequences generated to track the pandemic on the continent. These sequences have profoundly affected how public health officials in Africa have navigated the COVID-19 pandemic. RATIONALE We demonstrate how the first 100,000 SARS-CoV-2 sequences from Africa have helped monitor the epidemic on the continent, how genomic surveillance expanded over the course of the pandemic, and how we adapted our sequencing methods to deal with an evolving virus. Finally, we also examine how viral lineages have spread across the continent in a phylogeographic framework to gain insights into the underlying temporal and spatial transmission dynamics for several variants of concern (VOCs). RESULTS Our results indicate that the number of countries in Africa that can sequence the virus within their own borders is growing and that this is coupled with a shorter turnaround time from the time of sampling to sequence submission. Ongoing evolution necessitated the continual updating of primer sets, and, as a result, eight primer sets were designed in tandem with viral evolution and used to ensure effective sequencing of the virus. The pandemic unfolded through multiple waves of infection that were each driven by distinct genetic lineages, with B.1-like ancestral strains associated with the first pandemic wave of infections in 2020. Successive waves on the continent were fueled by different VOCs, with Alpha and Beta cocirculating in distinct spatial patterns during the second wave and Delta and Omicron affecting the whole continent during the third and fourth waves, respectively. Phylogeographic reconstruction points toward distinct differences in viral importation and exportation patterns associated with the Alpha, Beta, Delta, and Omicron variants and subvariants, when considering both Africa versus the rest of the world and viral dissemination within the continent. Our epidemiological and phylogenetic inferences therefore underscore the heterogeneous nature of the pandemic on the continent and highlight key insights and challenges, for instance, recognizing the limitations of low testing proportions. We also highlight the early warning capacity that genomic surveillance in Africa has had for the rest of the world with the detection of new lineages and variants, the most recent being the characterization of various Omicron subvariants. CONCLUSION Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve. This is important not only to help combat SARS-CoV-2 on the continent but also because it can be used as a platform to help address the many emerging and reemerging infectious disease threats in Africa. In particular, capacity building for local sequencing within countries or within the continent should be prioritized because this is generally associated with shorter turnaround times, providing the most benefit to local public health authorities tasked with pandemic response and mitigation and allowing for the fastest reaction to localized outbreaks. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century