Infection with mpox virus via the genital mucosae increases shedding and transmission in the multimammate rat (Mastomys natalensis).

The 2022 mpox virus (MPXV) outbreak was sustained by human-to-human transmission; however, it is currently unclear which factors lead to sustained transmission of MPXV. Here we present Mastomys natalensis as a model for MPXV transmission after intraperitoneal, rectal, vaginal, aerosol and transdermal inoculation with an early 2022 human outbreak isolate (Clade IIb). Virus shedding and tissue replication were route dependent and occurred in the presence of self-resolving localized skin, lung, reproductive tract or rectal lesions. Mucosal inoculation via the rectal, vaginal and aerosol routes led to increased shedding, replication and a pro-inflammatory T cell profile compared with skin inoculation. Contact transmission was higher from rectally inoculated animals. This suggests that transmission might be sustained by increased susceptibility of the anal and genital mucosae for infection and subsequent virus release.

A bivalent Adenovirus-Vectored Vaccine induces a robust humoral response, but does not protect cynomolgus macaques against a lethal challenge with Sudan virus.

The most recent Sudan virus (SUDV) outbreak in Uganda was first detected in September 2022 and resulted in 164 laboratory-confirmed cases and 77 deaths. There are no approved vaccines against SUDV. Here, we investigated the protective efficacy of ChAdOx1-biEBOV in cynomolgus macaques using a prime or a prime-boost regimen. ChAdOx1-biEBOV is a replication-deficient simian adenovirus vector encoding SUDV and Ebola virus (EBOV) glycoproteins (GPs). Intramuscular vaccination induced SUDV and EBOV GP-specific IgG responses and neutralizing antibodies. Upon challenge with SUDV, vaccinated animals showed signs of disease like those observed in control animals, and no difference in survival outcomes were measured among all three groups. Viral load in blood samples and in tissue samples obtained after necropsy were not significantly different between groups. Overall, this study highlights the importance of evaluating vaccines in multiple animal models and demonstrates the importance of understanding protective efficacy in both animal models and human hosts.

Sex differences and individual variability in the captive Jamaican fruit bat (Artibeus jamaicensis) intestinal microbiome and metabolome.

The intestinal microbiome plays an important role in mammalian health, disease, and immune function. In light of this function, recent studies have aimed to characterize the microbiomes of various bat species, which are noteworthy for their roles as reservoir hosts for several viruses known to be highly pathogenic in other mammals. Despite ongoing bat microbiome research, its role in immune function and disease, especially the effects of changes in the microbiome on host health, remains nebulous. Here, we describe a novel methodology to investigate the intestinal microbiome of captive Jamaican fruit bats (Artibeus jamaicensis). We observed a high degree of individual variation in addition to sex- and cohort-linked differences. The intestinal microbiome was correlated with intestinal metabolite composition, possibly contributing to differences in immune status. This work provides a basis for future infection and field studies to examine in detail the role of the intestinal microbiome in antiviral immunity.

Host and viral determinants of airborne transmission of SARS-CoV-2 in the Syrian hamster.

It remains poorly understood how SARS-CoV-2 infection influences the physiological host factors important for aerosol transmission. We assessed breathing pattern, exhaled droplets, and infectious virus after infection with Alpha and Delta variants of concern (VOC) in the Syrian hamster. Both VOCs displayed a confined window of detectable airborne virus (24-48 hr), shorter than compared to oropharyngeal swabs. The loss of airborne shedding was linked to airway constriction resulting in a decrease of fine aerosols (1-10 µm) produced, which are suspected to be the major driver of airborne transmission. Male sex was associated with increased viral replication and virus shedding in the air. Next, we compared the transmission efficiency of both variants and found no significant differences. Transmission efficiency varied mostly among donors, 0-100% (including a superspreading event), and aerosol transmission over multiple chain links was representative of natural heterogeneity of exposure dose and downstream viral kinetics. Co-infection with VOCs only occurred when both viruses were shed by the same donor during an increased exposure timeframe (24-48 hr). This highlights that assessment of host and virus factors resulting in a differential exhaled particle profile is critical for understanding airborne transmission.

Infection- or AZD1222 vaccine-mediated immunity reduces SARS-CoV-2 transmission but increases Omicron competitiveness in hamsters.

Limited data is available on the effect of vaccination and previous virus exposure on the nature of SARS-CoV-2 transmission and immune-pressure on variants. To understand the impact of pre-existing immunity on SARS-CoV-2 airborne transmission efficiency, we perform a transmission chain experiment using naïve, intranasally or intramuscularly AZD1222 vaccinated, and previously infected hamsters. A clear gradient in transmission efficacy is observed: Transmission in hamsters vaccinated via the intramuscular route was reduced over three airborne chains (approx. 60%) compared to naïve animals, whereas transmission in previously infected hamsters and those vaccinated via the intranasal route was reduced by 80%. We also find that the Delta B.1.617.2 variant outcompeted Omicron B.1.1.529 after dual infection within and between hosts in naïve, vaccinated, and previously infected transmission chains, yet an increase in Omicron B.1.1.529 competitiveness is observed in groups with pre-existing immunity against Delta B.1.617.2. This correlates with an increase in the strength of the humoral response against Delta B.1.617.2, with the strongest response seen in previously infected animals. These data highlight the continuous need to improve vaccination strategies and address the additional evolutionary pressure pre-existing immunity may exert on SARS-CoV-2.

Stability of Monkeypox Virus in Body Fluids and Wastewater.

An outbreak of human mpox infection in nonendemic countries appears to have been driven largely by transmission through body fluids or skin-to-skin contact during sexual activity. We evaluated the stability of monkeypox virus (MPXV) in different environments and specific body fluids and tested the effectiveness of decontamination methodologies. MPXV decayed faster at higher temperatures, and rates varied considerably depending on the medium in which virus was suspended, both in solution and on surfaces. More proteinaceous fluids supported greater persistence. Chlorination was an effective decontamination technique, but only at higher concentrations. Wastewater was more difficult to decontaminate than plain deionized water; testing for infectious MPXV could be a helpful addition to PCR-based wastewater surveillance when high levels of viral DNA are detected. Our findings suggest that, because virus stability is sufficient to support environmental MPXV transmission in healthcare settings, exposure and dose-response will be limiting factors for those transmission routes.

Host and viral determinants of airborne transmission of SARS-CoV-2 in the Syrian hamster.

It remains poorly understood how SARS-CoV-2 infection influences the physiological host factors important for aerosol transmission. We assessed breathing pattern, exhaled droplets, and infectious virus after infection with Alpha and Delta variants of concern (VOC) in the Syrian hamster. Both VOCs displayed a confined window of detectable airborne virus (24-48 h), shorter than compared to oropharyngeal swabs. The loss of airborne shedding was linked to airway constriction resulting in a decrease of fine aerosols (1-10µm) produced, which are suspected to be the major driver of airborne transmission. Male sex was associated with increased viral replication and virus shedding in the air. Next, we compared the transmission efficiency of both variants and found no significant differences. Transmission efficiency varied mostly among donors, 0-100% (including a superspreading event), and aerosol transmission over multiple chain links was representative of natural heterogeneity of exposure dose and downstream viral kinetics. Co-infection with VOCs only occurred when both viruses were shed by the same donor during an increased exposure timeframe (24-48 h). This highlights that assessment of host and virus factors resulting in a differential exhaled particle profile is critical for understanding airborne transmission.

Severe acute respiratory disease in American mink experimentally infected with SARS-CoV-2.

An animal model that fully recapitulates severe COVID-19 presentation in humans has been a top priority since the discovery of SARS-CoV-2 in 2019. Although multiple animal models are available for mild to moderate clinical disease, models that develop severe disease are still needed. Mink experimentally infected with SARS-CoV-2 developed severe acute respiratory disease, as evident by clinical respiratory disease, radiological, and histological changes. Virus was detected in nasal, oral, rectal, and fur swabs. Deep sequencing of SARS-CoV-2 from oral swabs and lung tissue samples showed repeated enrichment for a mutation in the gene encoding nonstructural protein 6 in open reading frame 1ab. Together, these data indicate that American mink develop clinical features characteristic of severe COVID-19 and, as such, are uniquely suited to test viral countermeasures.

Avatar Mice Underscore the Role of the T Cell-Dendritic Cell Crosstalk in Ebola Virus Disease and Reveal Mechanisms of Protection in Survivors.

Ebola virus disease (EVD) is a complex infectious disease characterized by high inflammation, multiorgan failure, the dysregulation of innate and adaptive immune responses, and coagulation abnormalities. Evidence accumulated over the last 2 decades indicates that, during fatal EVD, the infection of antigen-presenting cells (APC) and the dysregulation of T cell immunity preclude a successful transition between innate and adaptive immunity, which constitutes a key disease checkpoint. In order to better understand the contribution of the APC-T cell crosstalk to EVD pathophysiology, we have developed avatar mice transplanted with human, donor-specific APCs and T cells. Here, we show that the transplantation of T cells and APCs from Ebola virus (EBOV)-naive individuals into avatar mice results in severe disease and death and that this phenotype is dependent on T cell receptor (TCR)-major histocompatibility complex (MCH) recognition. Conversely, avatar mice were rescued from death induced by EBOV infection after the transplantation of both T cells and plasma from EVD survivors. These results strongly suggest that protection from EBOV reinfection requires both cellular and humoral immune memory responses. IMPORTANCE The crosstalk between dendritic cells and T cells marks the transition between innate and adaptive immune responses, and it constitutes an important checkpoint in EVD. In this study, we present a mouse avatar model in which T cell and dendritic cell interactions from a specific donor can be studied during EVD. Our findings indicate that T cell receptor-major histocompatibility complex-mediated T cell-dendritic cell interactions are associated with disease severity, which mimics the main features of severe EVD in these mice. Resistance to an EBOV challenge in the model was achieved via the transplantation of both survivor T cells and plasma.

Atypical and Unique Transmission of Monkeypox Virus during the 2022 Outbreak: An Overview of the Current State of Knowledge.

An ongoing monkeypox outbreak in non-endemic countries has resulted in the declaration of a public health emergency of international concern by the World Health Organization (WHO). Though monkeypox has long been endemic in regions of sub-Saharan Africa, relatively little is known about its ecology, epidemiology, and transmission. Here, we consider the relevant research on both monkeypox and smallpox, a close relative, to make inferences about the current outbreak. Undetected circulation combined with atypical transmission and case presentation, including mild and asymptomatic disease, have facilitated the spread of monkeypox in non-endemic regions. A broader availability of diagnostics, enhanced surveillance, and targeted education, combined with a better understanding of the routes of transmission, are critical to identify at-risk populations and design science-based countermeasures to control the current outbreak.

UV-C Light Completely Blocks Aerosol Transmission of Highly Contagious SARS-CoV-2 Variants WA1 and Delta in Hamsters.

Behavioral and medical control measures have not been effective in containing the spread of SARS-CoV-2 in large part due to the unwillingness of populations to adhere to "best practices". Ultraviolet light with wavelengths of between 200 and 280 nm (UV-C) and, in particular, germicidal ultraviolet light, which refers to wavelengths around 254 nm, have the potential to unobtrusively reduce the risk of SARS-CoV-2 transmission in enclosed spaces. We investigated the effectiveness of a strategy using UV-C light to prevent airborne transmission of the virus in a hamster model. Treatment of environmental air with 254 nm UV-C light prevented transmission of SARS-CoV-2 between individuals in a model using highly susceptible Syrian golden hamsters. The prevention of transmission of SARS-CoV-2 in a natural system by treating elements of the surrounding environment is one more weapon in the arsenal to combat COVID. The results presented indicate that coupling mitigation strategies utilizing UV-C light, along with current methods to reduce transmission risk, have the potential to allow a return to normal indoor activities.

Infection- or vaccine mediated immunity reduces SARS-CoV-2 transmission, but increases competitiveness of Omicron in hamsters.

Omicron has demonstrated a competitive advantage over Delta in vaccinated people. To understand this, we designed a transmission chain experiment using naïve, intranasally (IN) or intramuscularly (IM) vaccinated, and previously infected (PI) hamsters. Vaccination and previous infection protected animals from disease and virus replication after Delta and Omicron dual challenge. A gradient in transmission blockage was observed: IM vaccination displayed moderate transmission blockage potential over three airborne chains (approx. 70%), whereas, IN vaccination and PI blocked airborne transmission in >90%. In naïve hamsters, Delta completely outcompeted Omicron within and between hosts after dual infection in onward transmission. Although Delta also outcompeted Omicron in the vaccinated and PI transmission chains, an increase in Omicron competitiveness was observed in these groups. This correlated with the increase in the strength of the humoral response against Delta, with the strongest response seen in PI animals. These data highlight the continuous need to assess the emergence and spread of novel variants in populations with pre-existing immunity and address the additional evolutionary pressure this may exert on the virus.

OraSure InteliSwab™ Rapid Antigen Test Performance with the SARS-CoV-2 Variants of Concern-Alpha, Beta, Gamma, Delta, and Omicron.

The emergence of SARS-CoV-2 in the human population and the resulting COVID-19 pandemic have led to the development of various diagnostic tests. The OraSure InteliSwab™ COVID-19 Rapid Test is a recently developed and FDA emergency use-authorized rapid antigen-detecting test that functions as a lateral flow device targeting the nucleocapsid protein. Due to SARS-CoV-2 evolution, there is a need to evaluate the sensitivity of rapid antigen-detecting tests for new variants, especially variants of concern such as Omicron. In this study, the sensitivity of the OraSure InteliSwab™ Test was investigated using cultured strains of the known variants of concern (VOCs, Alpha, Beta, Gamma, Delta, and Omicron) and the ancestral lineage (lineage A). Based on dilution series in cell culture medium, an approximate limit of detection for each variant was determined. The OraSure InteliSwab™ Test showed an overall comparable performance using recombinant nucleocapsid protein and different cultured variants, with recorded limits of detection ranging between 3.77 × 105 and 9.13 × 105 RNA copies/mL. Finally, the sensitivity was evaluated using oropharyngeal swabs from Syrian golden hamsters inoculated with the six VOCs. Ultimately, the OraSure InteliSwab™ COVID-19 Rapid Test showed no decrease in sensitivity between the ancestral SARS-CoV-2 strain and any VOCs including Omicron.

OraSure InteliSwab ® Rapid Antigen Test performance with the SARS-CoV-2 Variants of Concern Alpha, Beta, Gamma, Delta, and Omicron.

The emergence of SARS-CoV-2 in the human population and the resulting COVID-19 pandemic has led to the development of various diagnostic tests. The OraSure InteliSwab ® COVID-19 Rapid Test is a recently developed and FDA emergency use authorized rapid antigen-detecting test that functions as a lateral flow device targeting the nucleocapsid protein. Due to SARS-CoV-2 evolution, there is a need to evaluate the sensitivity of rapid antigen-detecting tests for new variants, especially variants of concern like Omicron. In this study, the sensitivity of the OraSure InteliSwab ® Test was investigated using cultured strains of the known variants of concern (VOCs, Alpha, Beta, Gamma, Delta, and Omicron) and the ancestral lineage (lineage A). Based on dilution series in cell culture medium, an approximate limit of detection for each variant was determined. The OraSure InteliSwab ® Test showed an overall comparable performance using recombinant nucleocapsid protein and different cultured variants with recorded limits of detection ranging between 3.77 × 10 5 and 9.13 × 10 5 RNA copies/mL. Finally, the sensitivity was evaluated using oropharyngeal swabs from Syrian golden hamsters inoculated with the 6 VOCs. Ultimately, the OraSure InteliSwab ® COVID-19 Rapid Test showed no decrease in sensitivity between the ancestral SARS-CoV-2 strain and any VOCs including Omicron.

Age-related differences in immune dynamics during SARS-CoV-2 infection in rhesus macaques.

Advanced age is a key predictor of severe COVID-19. To gain insight into this relationship, we used the rhesus macaque model of SARS-CoV-2 infection. Eight older and eight younger macaques were inoculated with SARS-CoV-2. Animals were evaluated using viral RNA quantification, clinical observations, thoracic radiographs, single-cell transcriptomics, multiparameter flow cytometry, multiplex immunohistochemistry, cytokine detection, and lipidomics analysis at predefined time points in various tissues. Differences in clinical signs, pulmonary infiltrates, and virus replication were limited. Transcriptional signatures of inflammation-associated genes in bronchoalveolar lavage fluid at 3 dpi revealed efficient mounting of innate immune defenses in both cohorts. However, age-specific divergence of immune responses emerged during the post-acute phase. Older animals exhibited sustained local inflammatory innate responses, whereas local effector T-cell responses were induced earlier in the younger animals. Circulating lipid mediator and cytokine levels highlighted increased repair-associated signals in the younger animals, and persistent pro-inflammatory responses in the older animals. In summary, despite similar disease outcomes, multi-omics profiling suggests that age may delay or impair antiviral cellular immune responses and delay efficient return to immune homeostasis.

Increased small particle aerosol transmission of B.1.1.7 compared with SARS-CoV-2 lineage A in vivo.

The major transmission route for SARS-CoV-2 is airborne. However, previous studies could not elucidate the contribution between large droplets and aerosol transmission of SARS-CoV-2 and its variants. Here, we designed and validated an optimized transmission caging setup, which allows for the assessment of aerosol transmission efficiency at various distances. At a distance of 2 m, only particles of <5 µm traversed between cages. Using this setup, we investigated the relative efficiency of aerosol transmission between the SARS-CoV-2 Alpha variant (B.1.1.7) and lineage A in Syrian hamsters. Aerosol transmission of both variants was confirmed in all sentinels after 24 h of exposure as demonstrated by respiratory virus shedding and seroconversion. Productive transmission also occurred after 1 h of exposure, highlighting the efficiency of this transmission route. Interestingly, after donors were infected with a mix of both variants, the Alpha variant outcompeted the lineage A variant in an airborne transmission chain. Overall, these data indicate that a lower infectious dose of the Alpha variant, compared to lineage A, could be sufficient for successful transmission. This highlights the continuous need to assess emerging variants and the development for pre-emptive transmission mitigation strategies.

UV-C light completely blocks highly contagious Delta SARS-CoV-2 aerosol transmission in hamsters.

Behavioral and medical control measures are not effective in containing the spread of SARS-CoV-2. Here we report on the effectiveness of a preemptive environmental strategy using UV-C light to prevent airborne transmission of the virus in a hamster model and show that UV-C exposure completely prevents airborne transmission between individuals.

Ecology, evolution and spillover of coronaviruses from bats.

In the past two decades, three coronaviruses with ancestral origins in bats have emerged and caused widespread outbreaks in humans, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Since the first SARS epidemic in 2002-2003, the appreciation of bats as key hosts of zoonotic coronaviruses has advanced rapidly. More than 4,000 coronavirus sequences from 14 bat families have been identified, yet the true diversity of bat coronaviruses is probably much greater. Given that bats are the likely evolutionary source for several human coronaviruses, including strains that cause mild upper respiratory tract disease, their role in historic and future pandemics requires ongoing investigation. We review and integrate information on bat-coronavirus interactions at the molecular, tissue, host and population levels. We identify critical gaps in knowledge of bat coronaviruses, which relate to spillover and pandemic risk, including the pathways to zoonotic spillover, the infection dynamics within bat reservoir hosts, the role of prior adaptation in intermediate hosts for zoonotic transmission and the viral genotypes or traits that predict zoonotic capacity and pandemic potential. Filling these knowledge gaps may help prevent the next pandemic.