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Anosmia was identified as a hallmark of COVID-19 early in the pandemic, however, with the emergence of variants of concern, the clinical profile induced by SARS-CoV-2 infection has changed, with anosmia being less frequent. Here, we assessed the clinical, olfactory and neuroinflammatory conditions of golden hamsters infected with the original Wuhan SARS-CoV-2 strain, its isogenic ORF7-deletion mutant and three variants: Gamma, Delta, and Omicron/BA.1. We show that infected animals develop a variant-dependent clinical disease including anosmia, and that the ORF7 of SARS-CoV-2 contributes to the induction of olfactory dysfunction. Conversely, all SARS-CoV-2 variants are neuroinvasive, regardless of the clinical presentation they induce. Taken together, this confirms that neuroinvasion and anosmia are independent phenomena upon SARS-CoV-2 infection. Using newly generated nanoluciferase-expressing SARS-CoV-2, we validate the olfactory pathway as a major entry point into the brain in vivo and demonstrate in vitro that SARS-CoV-2 travels retrogradely and anterogradely along axons in microfluidic neuron-epithelial networks. Here, Dias de Melo et al. assess the clinical, olfactory, and neuroinflammatory conditions of golden hamsters infected with SARS-CoV-2 wt and VOCs and report that viruses can infect neurons, travel inside axons, and invade the central nervous system.

The currently licensed anti-tuberculosis (TB) vaccine, Mycobacterium bovis BCG, provides limited protection against pulmonary TB in adolescents and adults, the main cause of TB transmission and mortality. To obtain an improved BCG-based vaccine candidate with increased immune signalling but still low virulence, we have previously generated a recombinant BCG strain named BCG::ESX-1 Mmar , which is heterologously expressing ESX-1 functions of Mycobacterium marinum and thereby modulates the host innate immune responses via phagosomal rupture-associated induction of type I interferon production and enhanced inflammasome activity, leading to superior protection against TB disease in murine infection models. As protection may also vary with the route of vaccination, here, we have explored aerosol vaccination relative to subcutaneous vaccination, using BCG Pasteur and BCG::ESX-1 Mmar . We found that mice vaccinated via the aerosol route with BCG Pasteur or BCG::ESX-1 Mmar both yielded higher frequencies of CD4 + and CD8 + Th1 activated effectors and T effector memory cells in the lungs compared to subcutaneously immunised mice, whereas comparable polyfunctional Th1 (IL-2, TNF-α and IFN-γ) cytokine-producing subsets were observed in the spleens of all vaccinated mice. Significantly higher IL-17A responses without severe lung pathology were seen in the lungs of aerosol-vaccinated mice associated to local and transient inflammatory cytokine responses and immune cell infiltrations. In contrast to the subcutaneous route, aerosol vaccination elicited high amounts of humoral IgG and IgA responses in the bronchoalveolar lavage fluid and induced a substantial number of lung CD4 + and CD8 + T cells expressing CD69 + CD103 + tissue-residency markers. These effects led to significant improved protection against M. tuberculosis and reduced lung pathology in aerosol-vaccinated mice compared to subcutaneously vaccinated mice. Moreover, BCG::ESX-1 Mmar vaccine induced enhanced T-cell immunity and superior protection compared to parental BCG Pasteur for both vaccination routes and thereby represents an interesting candidate for developing improved vaccination strategies against TB.

Several COVID-19 vaccines have now been deployed to tackle the SARS-CoV-2 pandemic, most of them based on messenger RNA or adenovirus vectors.The duration of protection afforded by these vaccines is unknown, as well as their capacity to protect from emerging new variants. To provide sufficient coverage for the world population, additional strategies need to be tested. The live pediatric measles vaccine (MV) is an attractive approach, given its extensive safety and efficacy history, along with its established large-scale manufacturing capacity. We develop an MV-based SARS-CoV-2 vaccine expressing the prefusion-stabilized, membrane-anchored full-length S antigen, which proves to be efficient at eliciting strong Th1-dominant T-cell responses and high neutralizing antibody titers. In both mouse and golden Syrian hamster models, these responses protect the animals from intranasal infectious challenge. Additionally, the elicited antibodies efficiently neutralize in vitro the three currently circulating variants of SARS-CoV-2. Here the authors generate a measles virus-based vaccine expressing SARSCoV-2 spike protein and show immunogenicity and protection in mice and hamsters, including neutralization of circulating variants of concerns in vitro.

Following infection with SARS-CoV-2, patients may experience with one or more symptoms that appear or persist over time. Neurological symptoms associated with long COVID include anxiety, depression, and memory impairment. However, the exact underlying mechanisms are not yet fully understood. Using golden hamsters as a model, we provide further evidence that SARS-CoV-2 is neuroinvasive and can persistently infect the brain, as viral RNA and replicative virus are detected in the brainstem 80 days after the initial infection. Infected hamsters exhibit a neurodegenerative signature in the brainstem, characterized by overexpression of innate immunity genes, and altered expression of genes involved in the dopaminergic and glutamatergic synapses, in energy metabolism, and in proteostasis. These infected animals exhibit persistent depression-like behavior, impaired short-term memory, and late-onset signs of anxiety. Finally, we provide evidence that viral and immunometabolic mechanisms coexist in the brainstem of SARS-CoV-2-infected hamsters, contributing to the manifestation of neuropsychiatric and cognitive symptoms. SARS-CoV-2 persists in the brainstem long after the initial infection has passed. Infected animals exhibit symptoms of anxiety, depression, and memory impairment as well as changes in the brain that can be related to neurodegenerative processes.

The bacterial and fungal communities associated with dandruff were investigated using culture-independent methodologies in the French subjects. The major bacterial and fungal species inhabiting the scalp subject's were identified by cloning and sequencing of the conserved ribosomal unit regions (16S for bacterial and 28S-ITS for fungal) and were further quantified by quantitative PCR. The two main bacterial species found on the scalp surface were Propionibacterium acnes and Staphylococcus epidermidis, while Malassezia restricta was the main fungal inhabitant. Dandruff was correlated with a higher incidence of M. restricta and S. epidermidis and a lower incidence of P. acnes compared to the control population (p<0.05). These results suggested for the first time using molecular methods, that dandruff is linked to the balance between bacteria and fungi of the host scalp surface.

Infectious diseases have been paramount among the threats to health and survival throughout human evolutionary history. Natural selection is therefore expected to act strongly on host defense genes, particularly on innate immunity genes whose products mediate the direct interaction between the host and the microbial environment. In insects and mammals, the Toll-like receptors (TLRs) appear to play a major role in initiating innate immune responses against microbes. In humans, however, it has been speculated that the set of TLRs could be redundant for protective immunity. We investigated how natural selection has acted upon human TLRs, as an approach to assess their level of biological redundancy. We sequenced the ten human TLRs in a panel of 158 individuals from various populations worldwide and found that the intracellular TLRs -- activated by nucleic acids and particularly specialized in viral recognition -- have evolved under strong purifying selection, indicating their essential non-redundant role in host survival. Conversely, the selective constraints on the TLRs expressed on the cell surface -- activated by compounds other than nucleic acids -- have been much more relaxed, with higher rates of damaging nonsynonymous and stop mutations tolerated, suggesting their higher redundancy. Finally, we tested whether TLRs have experienced spatially-varying selection in human populations and found that the region encompassing TLR10-TLR1-TLR6 has been the target of recent positive selection among non-Africans. Our findings indicate that the different TLRs differ in their immunological redundancy, reflecting their distinct contributions to host defense. The insights gained in this study foster new hypotheses to be tested in clinical and epidemiological genetics of infectious disease.

Human leukocyte antigen-G (HLA-G) is an immunomodulatory molecule known to play a crucial role in immune tolerance and regulation. In the context of human African trypanosomiasis (HAT), higher soluble HLA-G levels were detected in the plasma of confirmed cases, representing a serological marker of T. b. gambiense infection. As trypanosomes also invade extravascular tissues, especially the skin, this study explored the potential role of HLA-G in the dermal immune response during T. b. gambiense infection. Blood and skin samples from 50 seronegative individuals, 45 seropositive suspects and 36 confirmed HAT cases, collected between 2018 and 2022 in endemic foci of Guinea and Côte d’Ivoire, were analyzed. Plasmatic and dermal levels of HLA-G proteins were quantified by ELISA and immuno-histochemistry, respectively, and compared to the trypanosome detection results in the same samples. The implication of soluble HLA-G plasma level as a biomarker of T. b. gambiense infection was confirmed. In the dermis, HLA-G isoforms were expressed either with a granular distribution or with in diffuse halos. Granular patterns of dermal HLA-G were directly associated with the presence of trypanosomes in the dermis. The presence of diffuse halos was correlated to higher sHLA-G levels in the plasma. In total, this study provides the first evidence of the involvement of HLA-G in the extravascular immune response against parasites, especially in the skin. It shows that HLA-G distribution in the extravascular compartment also represents a biomarker of trypanosome infection.

The skin is an anatomical reservoir for African trypanosomes, yet the prevalence of extravascular parasite carriage in the population at risk of gambiense Human African Trypanosomiasis (gHAT) remains unclear. Here, we conducted a prospective observational cohort study in the HAT foci of Forecariah and Boffa, Republic of Guinea. Of the 18,916 subjects serologically screened for gHAT, 96 were enrolled into our study. At enrolment and follow-up visits, participants underwent a dermatological examination and had blood samples and superficial skin snip biopsies taken for examination by molecular and immuno-histological methods. In seropositive individuals, dermatological symptoms were significantly more frequent as compared to seronegative controls. Trypanosoma brucei DNA was detected in the blood of 67% of confirmed cases (22/33) and 9% of unconfirmed seropositive individuals (3/32). However, parasites were detected in the extravascular dermis of up to 71% of confirmed cases (25/35) and 41% of unconfirmed seropositive individuals (13/32) by PCR and/or immuno-histochemistry. Six to twelve months after treatment, trypanosome detection in the skin dropped to 17% of confirmed cases (5/30), whereas up to 25% of unconfirmed, hence untreated, seropositive individuals (4/16) were still found positive. Dermal trypanosomes were observed in subjects from both transmission foci, however, the occurrence of pruritus and the PCR positivity rates were significantly higher in unconfirmed seropositive individuals in Forecariah. The lower sensitivity of superficial skin snip biopsies appeared critical for detecting trypanosomes in the basal dermis. These results are discussed in the context of the planned elimination of gHAT.

In the population at risk of gambiense human African trypanosomiasis (gHAT), the prevalence of extravascular parasite carriage remains unclear. Here, we conducted an observational clinical study in the hypo-endemic gHAT foci of Sinfra and Bonon in Côte d’Ivoire from 2019 to 2022. A total of 74 individuals were enrolled, including 45 suspects previously found positive at least once in a serological test for gHAT and followed by the national elimination programme of Côte d’Ivoire, as well as 29 seronegative controls. No significant differences between groups were observed for any epidemiological parameters and any clinical parameters at enrolment. Whereas trypanosome DNA was detected in the blood of 0/29 controls and 2/45 suspects, the presence of extravascular dermal trypanosomes was confirmed by immuno-histochemistry (fixed trypanosome cells) and/or PCR (trypanosome DNA) in about 1/3 of the suspects (14/45, 31%). However, no gambiense -specific test was found positive in the present study. Hence, the skin could represent an anatomical reservoir for African trypanosomes sustaining a low level of transmission in hypo-endemic foci.