Barcoded SARS-CoV-2 viruses define the impact of time and route of transmission on the transmission bottleneck in a Syrian hamster model.

The transmission bottleneck, defined as the number of viruses that transmit from one host to infect another, is an important determinant of the rate of virus evolution and the level of immunity required to protect against virus transmission. Despite its importance, SARS-CoV-2's transmission bottleneck remains poorly characterized, in part due to a lack of quantitative measurement tools. To address this, we adapted a SARS-CoV-2 reverse genetics system to generate a pool of >200 isogenic SARS-CoV-2 viruses harboring specific 6-nucleotide barcodes inserted in ORF10, a non-translated ORF. We directly inoculated donor Syrian hamsters intranasally with this barcoded virus pool and exposed a paired naïve contact hamster to each donor. Following exposure, the nasal turbinates, trachea, and lungs were collected, viral titers were measured, and the number of barcodes in each tissue were enumerated to quantify the transmission bottleneck. The duration and route (airborne, direct contact, and fomite) of exposure were varied to assess their impact on the transmission bottleneck. In airborne-exposed hamsters, the transmission bottleneck increased with longer exposure durations. We found that direct contact exposure produced the largest transmission bottleneck (average 27 BCs), followed by airborne exposure (average 16 BCs) then fomite exposure (average 8 BCs). Interestingly, we detected unique BCs in both the upper and lower respiratory tract of contact animals from all routes of exposure, suggesting that SARS-CoV-2 can directly infect hamster lungs. Altogether, these findings highlight the utility of barcoded viruses as tools to rigorously study virus transmission. In the future, barcoded SARS-CoV-2 will strengthen studies of immune factors that influence virus transmission.

UV-C Light Intervention as a Barrier against Airborne Transmission of SARS-CoV-2.

BACKGROUND: SARS-CoV-2 continues to impact human health globally, with airborne transmission being a significant mode of transmission. In addition to tools like vaccination and testing, countermeasures that reduce viral spread in indoor settings are critical. This study aims to assess the efficacy of UV-C light, utilizing the Violett sterilization device, as a countermeasure against airborne transmission of SARS-CoV-2 in the highly susceptible Golden Syrian hamster model. METHODS: Two cohorts of naïve hamsters were subjected to airborne transmission from experimentally infected hamsters; one cohort was exposed to air treated with UV-C sterilization, while the other cohort was exposed to untreated air. RESULTS: Treatment of air with UV-C light prevented the airborne transmission of SARS-CoV-2 from the experimentally exposed hamster to naïve hamsters. Notably, this protection was sustained over a multi-day exposure period during peak viral shedding by hamsters. CONCLUSIONS: These findings demonstrate the efficacy of the UV-C light to mitigate against airborne SARS-CoV-2 transmission. As variants continue to emerge, UV-C light holds promise as a tool for reducing infections in diverse indoor settings, ranging from healthcare facilities to households. This study reinforces the urgency of implementing innovative methods to reduce airborne disease transmission and safeguard public health against emerging biological threats.

Characterization of a SARS-CoV-2 EG.5.1 clinical isolate in vitro and in vivo.

EG.5.1 is a subvariant of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron XBB variant that is rapidly increasing in prevalence worldwide. However, the pathogenicity, transmissibility, and immune evasion properties of isolates of EG.5.1 are largely unknown. Here, we show that there are no obvious differences in growth ability and pathogenicity between EG.5.1 and XBB.1.5 in hamsters. We also demonstrate that, like XBB.1.5, EG.5.1 is transmitted more efficiently between hamsters compared to its predecessor, BA.2. In contrast, unlike XBB.1.5, we detect EG.5.1 in the lungs of four of six exposed hamsters, suggesting that the virus properties of EG.5.1 are different from those of XBB.1.5. Finally, we find that the neutralizing activity of plasma from convalescent individuals against EG.5.1 was slightly, but significantly, lower than that against XBB.1.5 or XBB.1.9.2. Our data suggest that the different virus properties after transmission and the altered antigenicity of EG.5.1 may be driving its increasing prevalence over XBB.1.5 in humans.

Hypoxia-regulated secretion of IL-12 enhances antitumor activity and safety of CD19 CAR-T cells in the treatment of DLBCL.

CD19-targeted chimeric antigen receptor-modified T (CD19 CAR-T) cell therapy has been demonstrated as one of the most promising therapeutic strategies for treating B cell malignancies. However, it has shown limited treatment efficacy for diffuse large B cell lymphoma (DLBCL). This is, in part, due to the tumor heterogeneity and the hostile tumor microenvironment. Human interleukin-12 (IL-12), as a potent antitumor cytokine, has delivered encouraging outcomes in preclinical studies of DLBCL. However, potentially lethal toxicity associated with systemic administration precludes its clinical application. Here, an armed CD19 CAR expressing hypoxia-regulated IL-12 was developed (CAR19/hIL12ODD). In this vector, IL-12 secretion was restricted to hypoxic microenvironments within the tumor site by fusion of IL-12 with the oxygen degradation domain (ODD) of HIF1α. In vitro, CAR19/hIL12ODD-T cells could only secrete bioactive IL-12 under hypoxic conditions, accompanied by enhanced proliferation, robust IFN-γ secretion, increased abundance of CD4+, and central memory T cell phenotype. In vivo, adoptive transfer of CAR19/hIL12ODD-T cells significantly enhanced regression of large, established DLBCL xenografts in a novel immunodeficient Syrian hamster model. Notably, this targeted and controlled IL-12 treatment was without toxicity in this model. Taken together, our results suggest that armed CD19 CARs with hypoxia-controlled IL-12 (CAR19/hIL12ODD) might be a promising and safer approach for treating DLBCL.

Evaluation of Ayush-64 (a Polyherbal Formulation) and Its Ingredients in the Syrian Hamster Model for SARS-CoV-2 Infection Reveals the Preventative Potential of Alstonia scholaris.

In the current study, we evaluated the efficacy of Ayush-64 (A64), a polyherbal formulation containing Alstonia scholaris (L.) R. Br. (A. scholaris), Caesalpinia crista L. (C. crista), Picrorhiza kurroa Royle ex Benth (P. kurroa), and Swertia chirata (Roxb.) H. Karst. (S. chirata) against COVID-19 in a Syrian hamster infection model. Preventative use of A64 resulted in the late-phase recovery of body weight loss in severe acquired respiratory syndrome coronavirus-2 (SARS-CoV-2)-infected hamsters, suppression of pro-inflammatory cytokines, and blunted pulmonary pathology. In addition, we also investigated the efficacy of individual ingredients of A64, viz., A. scholaris, C. crista, P. kurroa, and S. chirata, in the hamster model. The hamster challenge data showed robust anti-viral and immunomodulatory potential in A. scholaris, followed by P. kurroa. However, C. crista and S. chirata of A64 showed prominent immunomodulatory potential without limiting the lung viral load. In order to better understand the immunomodulatory potential of these herbal extracts, we used an in vitro assay of helper T cell differentiation and found that A. scholaris mediated a more profound suppression of Th1, Th2, and Th17 cell differentiation as compared to A64 and other ingredients. Taken together, our animal study data identifies the ameliorative potential of A64 in mitigating coronavirus disease-19 (COVID-19) pulmonary pathology. A. scholaris, a constituent extract of A64, showed relatively higher anti-viral and immunomodulatory potential against COVID-19. The present study warrants further investigations to identify the active pharmaceutical ingredients of A. scholaris for further studies.

Protective role of stratum corneum in percutaneous Leptospira infection in a hamster model.

Leptospira enters humans and animals through injured skin or mucous membranes by direct or indirect contact with urine excreted from infected reservoirs. Individuals with cut or scratched skin are at high risk of infection and are recommended to be protected from contact with Leptospira, but the risk of infection via skin without apparent wounds is unknown. We hypothesized that the stratum corneum of the epidermis might prevent percutaneous invasion of leptospires. We established a stratum corneum deficient model of hamsters using the tape stripping method. The mortality rate of hamsters lacking stratum corneum that were exposed to Leptospira was higher than that of controls with shaved skin, and was not significantly different from an epidermal wound group. These results indicated that the stratum corneum plays a critical role in protecting the host against leptospiral entry. We also examined the migration of leptospires through the monolayer of HaCaT cells (human keratinocyte cell line) using Transwell. The number of pathogenic leptospires penetrating the HaCaT cell monolayers was higher than that of non-pathogenic leptospires. Furthermore, scanning and transmission electron microscopic observations revealed that the bacteria penetrated the cell monolayers through both intracellular and intercellular routes. This suggested that pathogenic Leptospira can migrate easily through keratinocyte layers and is associated with virulence. Our study further highlights the importance of the stratum corneum as a critical barrier against the invasion of Leptospira found in contaminated soil and water. Hence, preventative measures against contact infection should be taken, even without visible skin wounds.

Challenges and Strategies for Developing Recombinant Vaccines against Leptospirosis: Role of Expression Platforms and Adjuvants in Achieving Protective Efficacy.

The first leptospiral recombinant vaccine was developed in the late 1990s. Since then, progress in the fields of reverse vaccinology (RV) and structural vaccinology (SV) has significantly improved the identification of novel surface-exposed and conserved vaccine targets. However, developing recombinant vaccines for leptospirosis faces various challenges, including selecting the ideal expression platform or delivery system, assessing immunogenicity, selecting adjuvants, establishing vaccine formulation, demonstrating protective efficacy against lethal disease in homologous challenge, achieving full renal clearance using experimental models, and reproducibility of protective efficacy against heterologous challenge. In this review, we highlight the role of the expression/delivery system employed in studies based on the well-known LipL32 and leptospiral immunoglobulin-like (Lig) proteins, as well as the choice of adjuvants, as key factors to achieving the best vaccine performance in terms of protective efficacy against lethal infection and induction of sterile immunity.

Activity of Sotrovimab against BQ.1.1 and XBB.1 Omicron sublineages in a hamster model.

The successive emergence of SARS-CoV-2 Omicron variants has completely changed the modalities of use of therapeutic monoclonal antibodies. Recent in vitro studies indicated that only Sotrovimab has maintained partial activity against BQ.1.1 and XBB.1. In the present study, we used the hamster model to determine whether Sotrovimab retains antiviral activity against these Omicron variants in vivo. Our results show that at exposures consistent with those observed in humans, Sotrovimab remains active against BQ.1.1 and XBB.1, although for BQ.1.1 the efficacy is lower than that observed against the first globally dominant Omicron sublineages BA.1 and BA.2.

Efficacy of Plant-Made Human Recombinant ACE2 against COVID-19 in a Golden Syrian Hamster Model.

Coronavirus disease 2019 (COVID-19) is a novel infectious respiratory disease caused by SARS-CoV-2. We evaluated the efficacy of a plant-based human recombinant angiotensin-converting enzyme 2 (hrACE2) and hrACE2-foldon (hrACE2-Fd) protein against COVID-19. In addition, we analyzed the antiviral activity of hrACE2 and hrACE2-Fd against SARS-CoV-2 using real-time reverse-transcription PCR and plaque assays. The therapeutic efficacy was detected using the Golden Syrian hamster model infected with SARS-CoV-2. Both hrACE2 and hrACE2-Fd inhibited SARS-CoV-2 by 50% at concentrations below the maximum plasma concentration, with EC50 of 5.8 µg/mL and 6.2 µg/mL, respectively. The hrACE2 and hrACE2-Fd injection groups showed a tendency for decreased viral titers in nasal turbinate tissues on day 3 after virus inoculation; however, this decrease was not detectable in lung tissues. Histopathological examination on day 9 after virus inoculation showed continued inflammation in the SARS-CoV-2 infection group, whereas decreased inflammation was observed in both the hrACE2 and hrACE2-Fd injection groups. No significant changes were observed at other time points. In conclusion, the potential therapeutic efficacy of plant-based proteins, hrACE2 and hrACE2-Fd, against COVID-19 was confirmed in a SARS-CoV-2-inoculated Golden Syrian hamster model. Further preclinical studies on primates and humans are necessary to obtain additional evidence and determine the effectiveness of these therapies.

G4-binding drugs, chlorpromazine and prochlorperazine, repurposed against COVID-19 infection in hamsters.

The COVID-19 pandemic caused by SARS-CoV-2 has caused millions of infections and deaths worldwide. Limited treatment options and the threat from emerging variants underline the need for novel and widely accessible therapeutics. G-quadruplexes (G4s) are nucleic acid secondary structures known to affect many cellular processes including viral replication and transcription. We identified heretofore not reported G4s with remarkably low mutation frequency across >5 million SARS-CoV-2 genomes. The G4 structure was targeted using FDA-approved drugs that can bind G4s - Chlorpromazine (CPZ) and Prochlorperazine (PCZ). We found significant inhibition in lung pathology and lung viral load of SARS-CoV-2 challenged hamsters when treated with CPZ or PCZ that was comparable to the widely used antiviral drug Remdesivir. In support, in vitro G4 binding, inhibition of reverse transcription from RNA isolated from COVID-infected humans, and attenuated viral replication and infectivity in Vero cell cultures were clear in case of both CPZ and PCZ. Apart from the wide accessibility of CPZ/PCZ, targeting relatively invariant nucleic acid structures poses an attractive strategy against viruses like SARS-CoV-2, which spread fast and accumulate mutations quickly.

Protection from COVID-19 disease in hamsters vaccinated with subunit SARS-CoV-2 S1 mucosal vaccines adjuvanted with different adjuvants.

Introduction: Adjuvant plays an important role in directing the immune responses induced by vaccines. In previous studies, we have shown that a mucosal SARS-CoV-2 S1 subunit vaccine adjuvanted with a combination of CpG, Poly I:C and IL-15 (named CP15) induced effective mucosal and systemic immunity and conferred nearly sterile protection against SARS-CoV-2 viral replication in macaque models. Methods: In this study, we used a hamster model, which mimics the human scenario and reliably exhibits severe SARS-CoV-2 disease similar to hospitalized patients, to investigate the protection efficacy of the vaccines against COVID-19 disease. We compared the weight loss, viral loads (VLs), and clinical observation scores of three different vaccine regimens. All three regimens consisted of priming/boosting with S1 subunit vaccines, but adjuvanted with alum and/or CP15 administrated by either intramuscular (IM) or intranasal (IN) routes: Group 1 was adjuvanted with alum/alum administrated IM/IM; Group 2 was alum-IM/CP15-IN; and Group 3 was CP15-IM/CP15-IN. Results: After challenge with SARS-CoV-2 WA strain, we found that the alum/CP15 group showed best protection against weight loss, while the CP15 group demonstrated best reduction of oral SARS-CoV-2 VLs, suggesting that the protection profiles were different. Sex differences for VL and clinical scores were observed. Humoral immunity was induced but not correlated with protection. Moreover, S1-specific binding antibody titers against beta, omicron BA.1, and BA.2 variants showed 2.6-, 4.9- and 2.8- fold reduction, respectively, compared to the Wuhan strain. Discussion: Overall, the data suggested that adjuvants in subunit vaccines determine the protection profiles after SARS-CoV-2 infection and that nasal/oral mucosal immunization can protect against systemic COVID-19 disease.

Clostridioides difficile Binary Toxin Binding Component Increases Virulence in a Hamster Model.

Background: Clostridioides difficile is the leading cause of hospital-acquired gastrointestinal infection, in part due to the existence of binary toxin (CDT)-expressing hypervirulent strains. Although the effects of the CDT holotoxin on disease pathogenesis have been previously studied, we sought to investigate the role of the individual components of CDT during in vivo infection. Methods: To determine the contribution of the separate components of CDT during infection, we developed strains of C difficile expressing either CDTa or CDTb individually. We then infected both mice and hamsters with these novel mutant strains and monitored them for development of severe illness. Results: Although expression of CDTb without CDTa did not induce significant disease in a mouse model of C difficile infection, we found that complementation of a CDT-deficient C difficile strain with CDTb alone restored virulence in a hamster model of C difficile infection. Conclusions: Overall, this study demonstrates that the binding component of C difficile binary toxin, CDTb, contributes to virulence in a hamster model of infection.

Pharmacological potential of Withania somnifera (L.) Dunal and Tinospora cordifolia (Willd.) Miers on the experimental models of COVID-19, T cell differentiation, and neutrophil functions.

Cytokine release syndrome (CRS) due to severe acute respiratory coronavirus-2 (SARS-CoV-2) infection leads to life-threatening pneumonia which has been associated with coronavirus disease (COVID-19) pathologies. Centuries-old Asian traditional medicines such as Withania somnifera (L.) Dunal (WS) and Tinospora cordifolia (Willd.) Miers (TC) possess potent immunomodulatory effects and were used by the AYUSH ministry, in India during the COVID-19 pandemic. In the present study, we investigated WS and TC's anti-viral and immunomodulatory efficacy at the human equivalent doses using suitable in vitro and in vivo models. While both WS and TC showed immuno-modulatory potential, WS showed robust protection against loss in body weight, viral load, and pulmonary pathology in the hamster model of SARS-CoV2. In vitro pretreatment of mice and human neutrophils with WS and TC had no adverse effect on PMA, calcium ionophore, and TRLM-induced ROS generation, phagocytosis, bactericidal activity, and NETs formation. Interestingly, WS significantly suppressed the pro-inflammatory cytokines-induced Th1, Th2, and Th17 differentiation. We also used hACE2 transgenic mice to further investigate the efficacy of WS against acute SARS-CoV2 infection. Prophylactic treatment of WS in the hACE2 mice model showed significant protection against body weight loss, inflammation, and the lung viral load. The results obtained indicate that WS promoted the immunosuppressive environment in the hamster and hACE2 transgenic mice models and limited the worsening of the disease by reducing inflammation, suggesting that WS might be useful against other acute viral infections. The present study thus provides pre-clinical efficacy data to demonstrate a robust protective effect of WS against COVID-19 through its broader immunomodulatory activity.

Low doses of 3-phenyl-lawsone or meglumine antimoniate delivery by tattooing route are successful in reducing parasite load in cutaneous lesions of Leishmania (Viannia) braziliensis-infected hamsters.

Current therapeutic ways adopted for the treatment of leishmaniasis are toxic and expensive including parasite resistance is a growing problem. Given this scenario, it is urgent to explore treatment alternatives for leishmaniasis. The aim of this study was to evaluate the effect of 3-phenyl-lawsone (3-PL) naphthoquinone on Leishmania (Viannia) braziliensis infection, both in vitro and in vivo, using two local routes of administration: subcutaneous (higher dose) and tattoo (lower dose). In vitro 3-PL showed low toxicity for macrophages (CC50 >3200 µM/48h) and activity against intracellular amastigotes (IC50 = 193 ± 19 µM/48h) and promastigotes (IC50 = 116 ± 26 µM/72h), in which induced increased ROS generation. Additionally, 3-PL up-regulated the production of cytokines such as tumor necrosis factor alpha (TNF-α), monocyte chemotactic protein 1 (MCP-1), interleukin-6 (IL-6) and IL-10 in infected macrophages. However, the anti-amastigote action was independent of nitric oxide production. Treatment of hamsters infected with L. (V.) braziliensis from one week after infection with 3-PL by subcutaneous (25 µg/Kg) or tattooing (2.5 µg/Kg) route, during 3 weeks (3 times/week) or 2 weeks (2 times/week) significantly decreased the parasite load (p<0.001) in the lesion. The reduction of parasite load by 3-PL treatment was comparable to reference drug meglumine antimoniate administered by the same routes (subcutaneous 1mg/Kg and tattoo 0.1mg/Kg). In addition, treatment started from five weeks after infection with 3-PL per tattoo also decreased the parasite load. These results show the anti-leishmanial effect of 3-PL against L. (V.) braziliensis and its efficacy by subcutaneous (higher dose) and tattoo (lower dose) routes. In addition, this study shows that drug delivery by tattooing the lesion allows the use of lower doses than the conventional subcutaneous route, which may support the development of a new therapeutic strategy that can be adopted for leishmaniasis.

Protection from COVID-19 with a VSV-based vaccine expressing the spike and nucleocapsid proteins.

Successful vaccine efforts countering the COVID-19 pandemic are centralized around the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) protein as viral antigen and have greatly reduced the morbidity and mortality associated with COVID-19. Since the start of this pandemic, SARS-CoV-2 has evolved resulting in new variants of concern (VOC) challenging the vaccine-established immunologic memory. We show that vaccination with a vesicular stomatitis virus (VSV)-based vaccine expressing the SARS-CoV-2 S plus the conserved nucleocapsid (N) protein was protective in a hamster challenge model when a single dose was administered 28 or 10 days prior to challenge, respectively. In this study, only intranasal vaccination resulted in protection against challenge with multiple VOC highlighting that the addition of the N protein indeed improved protective efficacy. This data demonstrates the ability of a VSV-based dual-antigen vaccine to reduce viral shedding and protect from disease caused by SARS-CoV-2 VOC.

Prophylactic treatment of Glycyrrhiza glabra mitigates COVID-19 pathology through inhibition of pro-inflammatory cytokines in the hamster model and NETosis.

Severe coronavirus disease (COVID-19) is accompanied by acute respiratory distress syndrome and pulmonary pathology, and is presented mostly with an inflammatory cytokine release, a dysregulated immune response, a skewed neutrophil/lymphocyte ratio, and a hypercoagulable state. Though vaccinations have proved effective in reducing the COVID-19-related mortality, the limitation of the use of vaccine against immunocompromised individuals, those with comorbidity, and emerging variants remains a concern. In the current study, we investigate for the first time the efficacy of the Glycyrrhiza glabra (GG) extract, a potent immunomodulator, against SARS-CoV-2 infection in hamsters. Prophylactic treatment with GG showed protection against loss in body weight and a 35%-40% decrease in lung viral load along with reduced lung pathology in the hamster model. Remarkably, GG reduced the mRNA expression of pro-inflammatory cytokines and plasminogen activator inhibitor-1 (PAI-1). In vitro, GG acted as a potent immunomodulator by reducing Th2 and Th17 differentiation and IL-4 and IL-17A cytokine production. In addition, GG also showed robust potential to suppress ROS, mtROS, and NET generation in a concentration-dependent manner in both human polymorphonuclear neutrophils (PMNs) and murine bone marrow-derived neutrophils (BMDNs). Taken together, we provide evidence for the protective efficacy of GG against COVID-19 and its putative mechanistic insight through its immunomodulatory properties. Our study provides the proof of concept for GG efficacy against SARS-CoV-2 using a hamster model and opens the path for further studies aimed at identifying the active ingredients of GG and its efficacy in COVID-19 clinical cases.

Potent monoclonal antibodies neutralize Omicron sublineages and other SARS-CoV-2 variants.

The emergence and global spread of the SARS-CoV-2 Omicron variants, which carry an unprecedented number of mutations, raise serious concerns due to the reduced efficacy of current vaccines and resistance to therapeutic antibodies. Here, we report the generation and characterization of two potent human monoclonal antibodies, NA8 and NE12, against the receptor-binding domain of the SARS-CoV-2 spike protein. NA8 interacts with a highly conserved region and has a breadth of neutralization with picomolar potency against the Beta variant and the Omicron BA.1 and BA.2 sublineages and nanomolar potency against BA.2.12.1 and BA.4. Combination of NA8 and NE12 retains potent neutralizing activity against the major SARS-CoV-2 variants of concern. Cryo-EM analysis provides the structural basis for the broad and complementary neutralizing activity of these two antibodies. We confirm the in vivo protective and therapeutic efficacies of NA8 and NE12 in the hamster model. These results show that broad and potent human antibodies can overcome the continuous immune escape of evolving SARS-CoV-2 variants.

Different inoculum of Leishmania braziliensis concentrations influence immunopathogenesis and clinical evolution in the ear dermis hamster model of cutaneous leishmaniasis.

The golden hamster (Mesocricetus auratus) is commonly used as a promising model for Leishmania braziliensis infection developing skin-ulcerated lesions. However, different protocols using high concentration of parasites inoculated in the footpad result in severe clinical disease. Here, we further investigate the outcome of the site of infection and concentration of L. braziliensis parasites inoculated on the immunopathogenesis and clinical evolution. Initially, hamsters were infected in the ear dermis or hind footpad with a concentration of 1 × 105 parasites. Animals infected in the ear dermis developed a disease, with an increased parasite load that more closely resembled human cutaneous leishmaniasis lesions comparing to the group infected in the footpad. Next, we evaluated if different parasite concentrations (104 , 105 and 106 ) inoculated in the ear dermis would impact the course and clinical aspects of infection. Hamsters infected with 104 and 105 parasites developed mild lesions compared to the group infected with 106 that presented severe and persistent lesions. The parasite load varied between the different parasite concentrations. The inflammatory response was more intense when infection was initiated with 106 parasites accompanied by an increased initial expression of IL-4, IL-10 and arginase in the lymph node followed by expression of both pro-and anti-inflammatory cytokines comparing to groups infected with 104 and 105 parasites. In conclusion, the number of parasites inoculated, and the initial site of infection could influence the inflammatory response, and clinical presentation. Our results suggest that the ear dermis infection model induces a chronic disease that relates to immunopathological aspects of CL natural infection.

Activity of omadacycline in vitro against Clostridioides difficile and preliminary efficacy assessment in a hamster model of C. difficile-associated diarrhoea.

OBJECTIVES: Antibiotics are associated with increased risk of Clostridioides difficile infection, which has limited treatment options. We assessed in vitro activity of omadacycline (an aminomethylcycline antibiotic) against the C. difficile infection strain and efficacy in a hamster model of C. difficile-associated diarrhoea. METHODS: Omadacycline, clindamycin, tigecycline, vancomycin, and metronidazole minimum inhibitory concentrations (MICs) for the infection-model strain (C. difficile ATCC 43596) were determined. Hamsters were pretreated with subcutaneous clindamycin (10 mg/kg) and infected 24 h later with C. difficile ATCC 43596; 24 h post infection, they received oral omadacycline (50 mg/kg/day), vancomycin (50 mg/kg/day), or vehicle for 5 days. Efficacy was reported as survival. RESULTS: Omadacycline was as active as tigecycline, vancomycin, and metronidazole (MIC 0.06 mg/L); clindamycin showed no activity. Median survival in hamsters was: 12 days, omadacycline; 2 days, vancomycin; 4 days, clindamycin pretreatment only. CONCLUSION: Omadacycline exhibited potent in vitro activity against C. difficile and showed efficacy in a model of C. difficile-associated diarrhoea.

Ivermectin Does Not Protect against SARS-CoV-2 Infection in the Syrian Hamster Model.

Ivermectin, an FDA-approved antiparasitic drug, has been reported to have in vitro activity against SARS-CoV-2. Increased off-label use of ivermectin for COVID-19 has been reported. We here assessed the effect of ivermectin in Syrian hamsters infected with the SARS-CoV-2 Beta (B.1.351) variant. Infected animals received a clinically relevant dose of ivermectin (0.4 mg/kg subcutaneously dosed) once daily for four consecutive days after which the effect was quantified. Ivermectin monotherapy did not reduce lung viral load and even significantly worsened SARS-CoV-2-induced lung pathology. Additionally, it did not potentiate the activity of molnupiravir (LagevrioTM) when combined with this drug. This study contributes to the growing body of evidence that ivermectin does not result in a beneficial effect in the treatment of COVID-19. These findings are important given the increasing, dangerous off-label use of ivermectin for the treatment of COVID-19.