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Usutu virus (USUV) is a flavivirus transmitted to avian species through mosquito bites that causes mass mortalities in wild and captive bird populations. However, several cases of positive dead birds have been recorded during the winter, a vector-free period. To explain how USUV "overwinters", the main hypothesis is bird-to-bird transmission, as shown for the closely related West Nile virus. To address this question, we experimentally challenged canaries with intranasal inoculation of USUV, which led to systemic dissemination of the virus, provided the inoculated dose was sufficient (>102 TCID50). We also highlighted the oronasal excretion of infectious viral particles in infected birds. Next, we co-housed infected birds with naive sentinels, to determine whether onward transmission could be reproduced experimentally. We failed to detect such transmission but demonstrated horizontal transmission by transferring sputum from an infected to a naive canary. In addition, we evaluated the cellular tropism of respiratory mucosa to USUV in vitro using a canary tracheal explant and observed only limited evidence of viral replication. Further research is then needed to assess if and how comparable bird-to-bird transmission occurs in the wild.

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Usutu virus (USUV) is a mosquito-borne flavivirus, closely related to the West Nile virus (WNV). Similar to WNV, USUV may cause infections in humans, with occasional, but sometimes severe, neurological complications. Further, USUV can be highly pathogenic in wild and captive birds and its circulation in Europe has given rise to substantial avian death. Adequate study models of this virus are still lacking but are critically needed to understand its pathogenesis and virulence spectrum. The chicken embryo is a low-cost, easy-to-manipulate and ethically acceptable model that closely reflects mammalian fetal development and allows immune response investigations, drug screening, and high-throughput virus production for vaccine development. While former studies suggested that this model was refractory to USUV infection, we unexpectedly found that high doses of four phylogenetically distinct USUV strains caused embryonic lethality. By employing immunohistochemistry and quantitative reverse transcriptase-polymerase chain reaction, we demonstrated that USUV was widely distributed in embryonic tissues, including the brain, retina, and feather follicles. We then successfully developed a primary cell line from the chorioallantoic membrane that was permissive to the virus without the need for viral adaptation. We believe the future use of these models would foster a significant understanding of USUV-induced neuropathogenesis and immune response and allow the future development of drugs and vaccines against USUV.

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Usutu virus (USUV) is a neurotropic flavivirus closely related to West Nile virus (WNV). Its enzootic cycle mainly involves mosquitoes and birds. Human infection can occur with occasional, but sometimes severe, neurological complications. Since its emergence and spread in Europe over the last two decades, USUV has been linked to significant avian outbreaks, especially among Passeriformes, including European blackbirds (Turdus merula). Strikingly, no in vivo avian model exists so far to study this arbovirus. The domestic canary (Serinus canaria) is a passerine, which is considered as a highly susceptible model of infection by WNV. Here, we experimentally challenged domestic canaries with two different doses of USUV. All inoculated birds presented detectable amounts of viral RNA in the blood and RNA shedding via feathers and droppings during the early stages of the infection, as determined by RT-qPCR. Mortality occurred in both infected groups (1/5 and 2/5, respectively) and was not necessarily correlated to a pure neurological disease. Subsequent analyses of samples from dead birds showed histopathological changes and virus tropism mimicking those reported in naturally infected birds. A robust seroconversion followed the infection in almost all the surviving canaries. Altogether, these results demonstrate that domestic canaries constitute an interesting experimental model for the study of USUV pathogenesis and transmission.

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Usutu virus (USUV) is a mosquito-borne flavivirus that shares many similarities with the closely related West Nile virus (WNV) in terms of ecology and clinical manifestations. Initially distributed in Africa, USUV emerged in Italy in 1996 and managed to co-circulate with WNV in many European countries in a similar mosquito-bird life cycle. The rapid geographic spread of USUV, the seasonal mass mortalities it causes in the European avifauna, and the increasing number of infections with neurological disease both in healthy and immunocompromised humans has stimulated interest in infection studies to delineate USUV pathogenesis. Here, we assessed the pathogenicity of two USUV isolates from a recent Belgian outbreak in immunocompetent mice. The intradermal injection of USUV gave rise to disorientation and paraplegia and was associated with neuronal death in the brain and spinal cord in a single mouse. Intranasal inoculation of USUV could also establish the infection; viral RNA was detected in the brain 15 days post-infection. Overall, this pilot study probes the suitability of this murine model for the study of USUV neuroinvasiveness and the possibility of direct transmission in mammals.

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Wildlife surveillance allowed the monitoring of the zoonotic mosquito-borne Usutu virus (USUV) in birds and bats (Pipistrellus pipistrellus) in southern Belgium in 2017 and 2018. USUV-RNA was detected in 69 birds (of 253) from 15 species, among which 7 species had not previously been reported to be susceptible to the infection. Similarly, 2 bats (of 10) were detected positive by reverse transcriptase quantitative polymerase chain reaction (RT-qPCR). USUV-associated lesions were mainly found in Eurasian Blackbirds (Turdus merula), in which USUV antigens were demonstrated by immunohistochemistry in the brain, heart, liver, kidney, intestine, and lung. Partial nonstructural protein 5 gene-based phylogenetic analysis showed several identical or closely related strains from 2016, 2017, and 2018 clustering together within Europe 3 or Africa 3 lineages. Further, one USUV strain detected in a common chaffinch (Fringilla coelebs) manifested a close genetic relationship with the European 1 strains circulating in Hungary and Austria. Our data provide evidence of USUV endemization in southern Belgium in local birds and bats, extension of the host range of the virus and ongoing virus introduction from abroad, likely by migratory birds. Our results highlight the need for vigilance in the forthcoming years toward new virus-associated outbreaks in birds and possible human infections in Belgium.

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While fatal infections caused by the Usutu virus appeared to concern only passerines (especially the blackbird) and Strigiformes (especially the great gray owl), we report herein that the virus also naturally causes a fatal disease in an anseriforme species, the common scoter (Melanitta nigra).

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We surveyed morphologic alterations in calves in Belgium that were naturally infected in utero by Schmallenberg virus (SBV) and born with deformities during January-March 2012. SBV-specific RNA was distributed unevenly in different tissues. Natural intrauterine SBV infection of calves might cause serious damage to the central nervous system and muscles.

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Respiratory syncytial virus (RSV), a prominent cause of airway morbidity in children, maintains an excessive hospitalization rate despite decades of research. Host factors are assumed to influence the disease severity. As a first step toward identifying the underlying resistance mechanisms, we recently showed that inbred mouse strains differ dramatically as regards their susceptibility to pneumonia virus of mice (PVM), the murine counterpart of RSV. PVM infection in mice has been shown to faithfully mimic the severe RSV disease in human infants. This study aimed at dissecting the remarkable PVM-resistance shown by the SJL/J strain. To characterize its genetic component, we assessed clinical, physiopathological, and virological resistance/susceptibility traits in large first (F1) and second (F2) generations obtained by crossing the SJL/J (resistant) and 129/Sv (susceptible) strains. Then, to acquire conclusive in vivo evidence in support of the hypothesis that certain radiosensitive hematopoietic cells might play a significant role in PVM-resistance, we monitored the same resistance/susceptibility traits in mock- and γ-irradiated SJL/J mice. Segregation analysis showed that (i) PVM-resistance is polygenic, (ii) the resistance alleles are recessive, and (iii) all resistance-encoding alleles are concentrated in SJL/J. Furthermore, there was no alteration of SJL/J PVM-resistance after immunosuppression by γ-irradiation, which suggests that adaptive immunity is not involved. We conclude that host resistance to pneumoviruses should be amenable to genetic dissection in this mouse model and that radioresistant lung epithelial cells and/or alveolar macrophages may control the clinical severity of pneumovirus-associated lung disease.

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The study describes cytochrome P450 1A1 (CYPA1) expression in the skin of different cetacean species (Megaptera novaeangliae, n=15; Stenella attenuata, n=7 and Stenella longirostris, n=24) from the Mozambique Channel island of Mayotte. Immunohistochemical examination was performed with a monoclonal antibody against scup cytochrome CYPA1. The sex was determined using a molecular approach consisting in the genotyping sex-specific genes. CYPA1 was detected at the junction between epidermis and blubber on dolphins only, mostly in the endothelial cells. Similar observation was obtained in the dermis of one M. novaeangliae. Immunohistochemical slides were scored to evaluate the expression of the CYPA1 and a higher expression was observed in S. longirostris, suggesting a higher exposure to pollutants for this species. The difference of expression between sexes was not significant.

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We describe Brucella sp. infection and associated lesions in a harbor porpoise (Phocoena phocoena) found on the coast of Belgium. The infection was diagnosed by immunohistochemistry, transmission electron microscopy, and bacteriology, and the organism was identified as B. ceti. The infection's location in the porpoise raises questions of abortion and zoonotic risks.

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Gammaherpesviruses are archetypal pathogenic persistent viruses. The known human gammaherpesviruses (Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus) are host-specific and therefore lack a convenient in vivo infection model. This makes related animal gammaherpesviruses an important source of information. Infection by murid herpesvirus 4 (MuHV-4), a virus originally isolated from bank voles (Myodes glareolus), was studied here. MuHV-4 infection of inbred laboratory mouse strains (Mus musculus) is commonly used as a general model of gammaherpesvirus pathogenesis. However, MuHV-4 has not been isolated from house mice, and no systematic comparison has been made between experimental MuHV-4 infections of mice and bank voles. This study therefore characterized MuHV-4 (strain MHV-68) infection of bank voles through global luciferase imaging and classical virological methods. As in mice, intranasal virus inoculation led to productive replication in bank vole lungs, accompanied by massive cellular infiltrates. However, the extent of lytic virus replication was approximately 1000-fold lower in bank voles than in mice. Peak latency titres in lymphoid tissue were also lower, although latency was still established. Finally, virus transmission was tested between animals maintained in captivity. However, as observed in mice, MuHV-4 was not transmitted between voles under these conditions. In conclusion, this study revealed that, despite quantitative differences, replication and the latency sites of MuHV-4 are comparable in bank voles and mice. Therefore, it appears that, so far, Mus musculus represents a suitable host for studying gammaherpesvirus pathogenesis with MuHV-4. Establishing transmission conditions in captivity will be a vital step for further research in this field.

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BACKGROUND: The morphopathological picture of a subset of equine myopathies is compatible with a primary mitochondrial disease, but functional confirmation in vivo is still pending. The cationic dye JC-1 exhibits potential-dependent accumulation in mitochondria that is detectable by a fluorescence shift from green to orange. As a consequence, mitochondrial membrane potential can be optically measured by the orange/green fluorescence intensity ratio. A flow cytometric standardized analytic procedure of the mitochondrial function of equine peripheral blood mononuclear cells is proposed along with a critical appraisal of the crucial questions of technical aspects, reproducibility, effect of time elapsed between blood sampling and laboratory processing and reference values. RESULTS: The JC-1-associated fluorescence orange and green values and their ratio were proved to be stable over time, independent of age and sex and hypersensitive to intoxication with a mitochondrial potential dissipator. Unless time elapsed between blood sampling and laboratory processing does not exceed 5 hours, the values retrieved remain stable. Reference values for clinically normal horses are given. CONCLUSION: Whenever a quantitative measurement of mitochondrial function in a horse is desired, blood samples should be taken in sodium citrate tubes and kept at room temperature for a maximum of 5 hours before the laboratory procedure detailed here is started. The hope is that this new test may help in confirming, studying and preventing equine myopathies that are currently imputed to mitochondrial dysfunction.

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