Mucosal Immunity

Despite signs of infection—including taste loss, dry mouth and mucosal lesions such as ulcerations, enanthema and macules—the involvement of the oral cavity in coronavirus disease 2019 (COVID-19) is poorly understood. To address this, we generated and analyzed two single-cell RNA sequencing datasets of the human minor salivary glands and gingiva (9 samples, 13,824 cells), identifying 50 cell clusters. Using integrated cell normalization and annotation, we classified 34 unique cell subpopulations between glands and gingiva. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral entry factors such as ACE2 and TMPRSS members were broadly enriched in epithelial cells of the glands and oral mucosae.

Using orthogonal RNA and protein expression assessments, we confirmed SARS-CoV-2 infection in the glands and mucosae. Saliva from SARS-CoV-2-infected individuals harbored epithelial cells exhibiting ACE2 and TMPRSS expression and sustained SARS-CoV-2 infection. Acellular and cellular salivary fractions from asymptomatic individuals were found to transmit SARS-CoV-2 ex vivo. Matched nasopharyngeal and saliva samples displayed distinct viral shedding dynamics, and salivary viral burden correlated with COVID-19 symptoms, including taste loss. Upon recovery, this asymptomatic cohort exhibited sustained salivary IgG antibodies against SARS-CoV-2. Collectively, these data show that the oral cavity is an important site for SARS-CoV-2 infection and implicate saliva as a potential route of SARS-CoV-2 transmission. 

Published in Nature Medicine (March 25, 2021):

https://doi.org/10.1038/s41591-021-01296-8 

Compared with nasal swabs, saliva tests may better reflect infection deep in the lungs.  To the known risk factors for developing severe COVID-19—age, male sex, or any of a series of underlying conditions—a new study adds one more: high levels of the virus in your saliva. Standard COVID-19 tests sample the nasal passage. But several new tests look for SARS-CoV-2, the pandemic coronavirus, in saliva, and the new work finds a striking correlation between high virus levels there and later hospitalization or death. If the results are confirmed, saliva tests could help doctors prioritize which patients in the early stages of the disease should receive medicines that drive down levels of the virus. “I thought it was pretty striking,” says Shane Crotty, a virologist at the La Jolla Institute for Immunology, who was not involved with the research. Crotty notes the results suggest virus levels in saliva reflect viral load deep in the lungs, where the disease does much of its damage in severe cases. “That is a fundamentally valuable insight,” Crotty says. The new work isn’t the first to link the body’s coronavirus load and disease outcome. Several research groups have found a correlation between high viral levels in the nasal passages at the time of a patient’s hospital admission and ultimate disease severity. But other groups have failed to find that same link. The standard test to detect SARS-CoV-2 samples nasal mucus using nasopharyngeal (NP) swabs. The procedure is unpleasant, but it is the customary way to sample respiratory pathogens. In recent months, however, several research groups have developed and received emergency use authorization from the U.S. Food and Drug Administration for tests detecting SARS-CoV-2 in saliva. Yale University researchers were among the first, and the university’s hospitals have been using both saliva and NP swab tests. In both cases, labs analyze the samples using quantitative reverse transcription polymerase chain reaction tests, which can detect genetic material from SARS-CoV-2 and quantify the number of viral particles in each milliliter of sample.

Researchers led by Akiko Iwasaki, an immunologist at Yale, compared viral loads in saliva and NP swabs from 154 patients and 109 people without the virus. They divided the patients into groups that had low, medium, and high viral loads as determined by both types of test. Then they compared those results with the severity of symptoms the patients developed later. They found that patients who developed severe disease, were hospitalized, or died were more likely to have had high virus loads in their saliva tests, but not in their NP swabs. Viral load in both saliva and nasal mucus declined over time in patients who recovered, but not in those who died. When Iwasaki and her colleagues reviewed patients’ electronic medical records for markers of disease in the blood, they found that high saliva viral loads correlated with high levels of immune signals such as cytokines and chemokines, nonspecific molecules that ramp up in response to viral infections and have been linked to tissue damage. People with more virus in their saliva also gradually lost certain cells that mount an immune response against viral targets, had lower levels of antibodies targeting the spike protein that the virus uses to enter cells, and were slower to develop the strong immune response needed to knock down the virus in cases where they recovered. The team’s results appeared on 10 January in a preprint that has not been peer reviewed.

Iwasaki and her colleagues argue that saliva may be a better predictor of disease outcome than nasal mucus because the latter comes from the upper respiratory tract, whereas severe disease is associated with damage deep in the lungs. “Saliva may better represent what is going on in the lower respiratory tract,” Iwasaki says, because cilia lining the respiratory tract naturally move mucus up from the lungs into the throat, where it mixes with saliva; coughs have the same effect. The results don’t have enough statistical power to reveal how much more likely a person with a high saliva viral load is to develop severe COVID-19, Iwasaki says. She is also eager for other groups to replicate the results, especially because efforts to link high NP swab viral loads with disease progression have had mixed results. If other research confirms the finding, “it would clear away a lot of the fog” around this disease, Crotty says. Monica Gandhi, an infectious disease expert at the University of California, San Francisco, adds that if saliva tests are predictive, they could help doctors identify patients to treat early with either antibodies to reduce viral load or steroids to tamp down overactive nonspecific immune responses. Saliva tests are cheaper and easier than NP tests, but much less widely available. So confirmation of the new results could bolster efforts to make saliva tests more readily available, says Sri Kosuri, CEO of Octant, Inc., a biotech company. “If this study happened in March, we’d be talking about whether we should be doing NP testing at all,” Kosuri says.

Preprint available in medRxiv  (Jan. 10, 2021):

https://doi.org/10.1101/2021.01.04.21249236 

Cells in the nasal passages and upper airways are likely the coronavirus' major point of entry into the body, according to a study by Stanford Medicine researchers.

Le virus responsable du syndrome respiratoire aigu sévère 2 (SARS-CoV-2) est un Betacoronavirus de la famille des Coronaviridae. Il est responsable de la maladie appelée Covid-19. Les premiers cas d’infection au SARS-CoV-2 ont été rapportés en décembre 2019, dans la province de Wuhan en Chine. Depuis, le virus s’est propagé sur tous les continents, provoquant une pandémie. Comme la majorité des virus respiratoires, le SARS-CoV-2 se transmet principalement par voie aérienne, sous forme de gouttelettes. Ces gouttelettes se déposent sur des surfaces et vecteurs inertes (« fomites »). Le virus peut ensuite être transmis par contact avec ces surfaces (OMS 2020). Il est donc crucial dans la lutte contre la propagation du virus de disposer de moyens de décontamination surfacique. Ce travail s’inscrit dans cet objectif d’évaluer l’efficacité virucide sur le SARS-CoV-2 de différents biocides appliqués à la décontamination de surface. Les laboratoires et hôpitaux utilisent le plus souvent des solutions commerciales, telles que l’Anioxy-Spray™, le Surfa’Safe™ (Laboratoires ANIOS) et le Septalkan™ (Alkapharm), pour la décontamination des objets et plans de travail selon une action volontaire, sous la forme d’une pulvérisation dirigée sur les surfaces à traiter. Toutes ces solutions sont indiquées comme étant efficaces sur les virus (Laboratoire ANIOS, n.d.; Laboratoires ANIOS, n.d.; Alkapharm, n.d.), selon les normes EN 14 476, EN 13 610 et EN 14 675. D’autres produits chimiques plus communs, que nous pourrions appeler «grand public», peuvent aussi présenter des propriétés biocides. Citons par exemple l’éthanol (principal principe actif du gel hydro-alcoolique), efficace en milieu liquide sur les coronavirus SARS-CoV-1 (responsable de l’épidémie de 2003), MERS-CoV (coronavirus du syndrome respiratoire du Moyen-Orient) et SARS-CoV-2 (Kratzel et al. 2020 ; Kariwa et al. 2004), l’Eau de Javel, à une concentration minimale de 500 ppm en chlore (Lai et al. 2005) ou bien encore le vinaigre d’alcool, à une concentration de 6 % en acidité (Rabenau et al. 2005) efficaces en phase liquide sur le SARS-CoV-1. Enfin, des biocides utilisés dans des secteurs non médicaux ou de laboratoire peuvent aussi être utiles dans la lutte contre le SARS-CoV-2. Il s’agit par exemple du Bactipal ELV™; une solution à base d’acide peracétique (5 %), de peroxyde d’hydrogène et d’acide acétique utilisée en horticulture (homologuée par le Ministère de l’Agriculture et de l’Alimentation). Il présente une activité virucide à une concentration finale de 2 % (JohnsonDiversey, n.d.). L’objectif du travail présenté ici n’est pas d’aboutir à une normalisation de ces produits biocides. Il s’agit pour nous de vérifier leur activité, déjà éprouvée contre d’autres micro-organismes, sur des dépôts de SARS-CoV-2 en suspension dans une matrice comportant deux niveaux d’interférents, décrits par la norme NF EN 14 675, représentatives de conditions réelles de travail ou de circonstances de la vie quotidienne (salissures ménagères par exemple). Toutes les études avec du virus vivant ont été réalisées dans un laboratoire de niveau de sécurité biologique 3 (NSB3) selon les recommandations de la SFM (SFM avril 2020). Le matériel et méthode détaillé est présenté en annexe de ce texte. Brièvement, 10 µL d’une suspension virale à 2×106 pfu/mL, soit 2×104 pfu, ont été déposés sur des cupules stériles en inox de 9 mm de diamètre. Cette concentration est une condition majorante par rapport à des niveaux de contamination observés dans des prélèvements humains et des prélèvements de surface en milieu hospitalier (Wölfel et al. 2020, Ong et al. 2020). Les dépôts ont été séchés à température ambiante pendant 40 minutes. Cette étape de séchage engendre une chute de titre viral de 1,2 ± 0,6 log10 . A l’issue du séchage, une solution biocide a été appliquée sur la surface de la cupule. Le tableau 1 récapitule les résultats de ces évaluations. La réduction du titre viral est calculée par rapport à la moyenne des titres viraux des contrôles non traités par le biocide, correspondant à un dépôt de 10 µL de suspension virale séché pendant 40 minutes en même temps que les dépôts des cupules traitées. Les cupules témoin ne reçoivent pas de biocide mais subissent le même temps de séchage que les cupules essais. Les conditions pour lesquelles aucune particule virale n’a pu être mise en évidence après traitement figurent dans les cases grisées.

To assess the temporal dynamics of Middle East respiratory syndrome coronavirus (MERS-CoV) infection in dromedary camels, specimens were collected at 1–2 month intervals from 2 independent groups of animals during April 2013–May 2014 in ...

The results of 3 new studies reveal unknown ways until now that COVID-19 spreads, leading scientists to urge the use of face coverings in public. Research from various parts of the world considered three separate factors in each study: low humidity, public restrooms and airborne dust. The implications from all three of these studies? Mask up!

Low Humidity

A study just published in Transboundary and Emerging Diseases confirms an earlier study conducted in the Greater Sydney, Australia area during the early stages of the pandemic that reported a link between low humidity and community spread of COVID-19. The new research led by Dr. Michael Ward in the Sydney School of Veterinary Science adds to the growing body of evidence that low humidity is a key factor in the spread of the Coronavirus. The scientists estimated that for a 1% decrease in relative humidity, COVID-19 cases increase by 7 to 8%. The same link was not found in other weather patterns such as rainfall, temperature or wind. According to Ward, dry air favors the spread of the virus: “”When the humidity is lower, the air is drier and it makes the aerosols smaller,” he said, adding that aerosols are smaller than droplets. “When you sneeze and cough those smaller infectious aerosols can stay suspended in the air for longer. That increases the exposure for other people. When the air is humid and the aerosols are larger and heavier, they fall and hit surfaces quicker.” These findings add to a growing body of research that recommends wearing a mask.

Public Restrooms

A second study conducted by Chinese researchers from Yangzhou University reported that flushing a public restroom toilet or urinal can release clouds of virus-laden aerosols that can be inhaled, posing a serious public health challenge. The scientists simulated and tracked virus-laden particle movements when toilets and urinals were flushed. They discovered that flushing involves an interaction between gas and liquid, resulting in a large spread of aerosol particles. The disturbing results revealed that the trajectory of the particles ejected from flushing showed that more than 57% of the particles traveled away from the urinal. The researchers further point out that when men use urinals in a public restroom, these tiny particles can reach their thigh within 5.5 seconds when compared to the toilet flush, which takes 35 seconds to reach slightly higher. “From our work, it can be inferred that urnial flushing indeed promotes the spread of bacteria and viruses,” said Xiang-Dong Liu, one of the study’s authors. “Wearing a mask should be mandatory within public restrooms during the pandemic, and anti-diffusion improvements are urgently needed to prevent the spread of COVID-19.”

Airborne Dust

A third study from the University of California, Davis and the Icahn School of Medicine at Mt. Sinai reported that influenza viruses can spread through the air on dust, fibers and other microscopic particles. Until now, scientists assumed airborne transmission occurred mainly due to respiratory droplets by coughing, sneezing or talking. The scientists examined whether tiny, non-respiratory particles could carry influenza between guinea pigs. Using an automated particle sizer to count airborne particles, they found that uninfected guinea pigs give off spikes of up to 1,000 particles per second as they move around the cage. Particles given off by the animals’ breathing were at a constant but lower rate. Immune guinea pigs with influenza virus painted on their fur could transmit the virus through the air to other, susceptible guinea pigs, showing that the virus did not have to come directly from the respiratory tract to be infectious. Next the researchers tested whether microscopic fibers from an inanimate object could carry infectious viruses. They treated paper facial tissues with influenza virus, let them dry out and then crumpled them in front of the automated particle sizer. Crumpling the tissues released up to 900 particles per second in a size range that could be inhaled. They were also able to infect cells from these particles released from the virus-contaminated paper tissues. According to the researchers, the surprising findings that dust can spread viruses have obvious implications for Coronavirus transmission and use of masks for protection. Plus, they said, it opens up an entire new field of investigation on how outbreaks are interpreted.

Original studies available in these sites:

https://doi.org/10.1063/5.0021450

https://doi.org/10.1038/s41467-020-17888-w

https://doi.org/10.1111/tbed.13766

The pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first reported in Wuhan City, China, in 2019. After that, the outbreak has grown into a global pandemic and definite treatment for the disease, termed coronavirus disease 2019 (COVID-19), is currently unavailable.

Middle East respiratory syndrome coronavirus (MERS-CoV) causes severe acute respiratory symptoms. Due to the lack of medical countermeasures, effective and safe vaccines against MERS-CoV infection are urgently required.

Several of the nasal and oral rinses have been found to have a strong ability to neutralise human coronavirus, which suggests that these products may have the potential to reduce the amount of virus spread by people who are Covid-19 positive.

Middle East respiratory syndrome coronavirus (MERS-CoV) has caused human respiratory infections with a high case fatality rate since 2012. However, the mode of virus transmission is not well understood.