The African swine fever virus isolate Belgium 2018/1 shows high virulence in European wild boar

African swine fever (ASF) is one of the most important and complex viral diseases in domestic pigs and wild boar. Over the last decade, the disease has spread to several European and Asian countries and is now one of the major threats to profitable pig production worldwide. One of the more recently affected western countries is Belgium. To date, only wild boar are affected in a rather defined area in the Luxembourg region close to France, Luxembourg and Germany. While detailed sequence analyses were recently performed, biological characterization was still pending. Here, we report on the experimental inoculation of four sub-adult wild boar to further characterize the virus and its distribution in different tissues. After oronasal inoculation with the virus strain 'Belgium 2018/1', all animals developed an acute and severe disease course with typical pathomorphological and histopathological lesions. Organs and blood samples were positive in qPCR, haemadsorption test and antigen lateral flow devices (LFD). Virus and viral genome were also detected in genitals and accessory sex glands of two boars. There were no antibodies detectable in commercial antibody ELISAs, antibody LFDs and indirect immunoperoxidase tests. Thus, the genotype II ASF virus isolate 'Belgium 2018/1' showed a highly virulent phenotype in European wild boar similar to parental viruses like Armenia 2007 and other previously characterized ASFV strains. The study also provided a large set of well-characterized sample materials for test validation and assay harmonization.

Viral-host interaction in kidney reveals strategies to escape host immunity and persistently shed virus to the urine

Hepatitis A virus is one of five types of hepatotropic viruses that cause human liver disease. A similar liver disease is also identified in ducks caused by Duck Hepatitis A virus (DHAV). Notably, many types of hepatotropic viruses can be detected in urine. However, how those viruses enter into the urine is largely unexplored. To elucidate the potential mechanism, we used the avian hepatotropic virus to investigate replication strategies and immune responses in kidney until 280 days after infection. Immunohistochemistry and qPCR were used to detect viral distribution and copies in the kidney. Double staining of CD4+ or CD8+ T cells and virus and qPCR were used to investigate T cell immune responses and expression levels of cytokines. Histopathology was detected by standard HE staining. In this study, viruses were persistently located at scattered renal tubules. No CD4+ or CD8+ T cells were recruited to the kidney, which was only accompanied by transient cytokine storms. In conclusion, the extremely scattered infection was the viral strategy to escape host immunity and may persistently shed virus into urine. The deletion of Th or Tc cell responses and transient cytokine storms indeed provide an advantageous renal environment for their persistent survival.

Distribution of Viral Antigen and Inflammatory Lesions in the Central Nervous System of Cockatiels ( Nymphicus hollandicus) Experimentally Infected with Parrot Bornavirus 2

Neurotropism is a striking characteristic of bornaviruses, including parrot bornavirus 2 (PaBV-2). Our study evaluated the distribution of inflammatory foci and viral nucleoprotein (N) antigen in the brain and spinal cord of 27 cockatiels ( Nymphicus hollandicus) following experimental infection with PaBV-2 by injection into the pectoral muscle. Tissue samples were taken at 12 timepoints between 5 and 114 days post-inoculation (dpi). Each experimental group had approximately 3 cockatiels per group and usually 1 negative control. Immunolabeling was first observed within the ventral horns of the thoracic spinal cord at 20 dpi and in the brain (thalamic nuclei and hindbrain) at 25 dpi. Both inflammation and viral antigen were restricted to the central core of the brain until 40 dpi. The virus then spread quickly at 60 dpi to both gray and white matter of all analyzed sections of the central nervous system (CNS). Encephalitis was most severe in the thalamus and hindbrain, while myelitis was most prominent in the gray matter and equally distributed in the cervical, thoracic, and lumbosacral spinal cord. Our results demonstrate a caudal to rostral spread of virus in the CNS following experimental inoculation of PABV-2 into the pectoral muscle, with the presence of viral antigen and inflammatory lesions first in the spinal cord and progressing to the brain.

LPAIV H9N2 Drives the Differential Expression of Goose Interferons and Proinflammatory Cytokines in Both In Vitro and In Vivo Studies

Geese, as aquatic birds, are an important natural reservoir of avian influenza virus (AIV). To characterize the innate antiviral immune response against AIV H9N2 strain infection in geese as well as the probable relationship between the expression of immune-related genes and the distribution of viral antigens, we investigated the levels of immune-related gene transcription both in AIV H9N2 strain-infected geese and in vitro. The patterns of viral location and the tissue distribution of CD4- and CD8α-positive cells were concurrently detected by immunohistochemical staining, which revealed respiratory and digestive organs as the primary sites of antigen-positive signals. Average AIV H9N2 viral loads were detected in the feces, Harderian gland (HG), and trachea, where higher copy numbers were detected compared with the rectum. Our results suggested the strong induction of proinflammatory cytokine expression compared with interferons (IFNs). Notably, in most tissues from the AIV H9N2 strain-infected birds, IFNα and IFNγ gene transcripts were differentially expressed. However, inverse changes in IFNα and IFNγ expression after AIV H9N2 strain infection were observed in vitro. Taken together, the results suggest that AIV H9N2 is widely distributed in multiple tissues, efficiently induces inflammatory cytokines in the HG and spleen of goslings and inversely influences type I and II IFN expression both in vivo and in vitro. The findings of this study further our understanding of host defense mechanisms and the pathogenesis of the H9N2 influenza virus in geese.

Detection of nidoviruses in samples collected from captive snakes in Europe between 2016 and 2021

BACKGROUND

Nidoviruses are increasingly detected in various snake species worldwide, but much remains to be learned about their distribution and the factors influencing their epidemiology.

METHODS

This retrospective study evaluated the results of routine nidovirus testing, by PCR, of 5210 swab samples from pet snakes from various European countries that were submitted to a commercial veterinary laboratory in Germany between 2016 and 2021.

RESULTS

The overall detection rate was 19.96%. However, the detection rate varied significantly depending on the snake species (p < 0.0001), with the highest rate in Indian pythons (Python molurus) (42.24%). Rates also varied depending on the season of sample collection (p < 0.0001), with the highest rate in winter (24.46%), and the country of sample origin (p < 0.0001), with the highest rate in Austria (36.69%). The detection rate also decreased significantly (p = 0.0003) over the 6-year observation period, from 26.43% to 17.64%.

LIMITATION

No information on clinical signs was available for most of the sampled snakes.

CONCLUSION

The present study supplies new information on the distribution of python nidoviruses (subgenus Roypretovirus) in pet snakes in Europe and indicates a dynamic situation with possible changes in prevalence over time.

A Novel Mastadenovirus from Nyctalus noctula Which Represents a Distinct Evolutionary Branch of Viruses from Bats in Europe

Bats are natural hosts of a wide variety of viruses, including adenoviruses. European bats are known to carry mastadenoviruses categorized as species B (widespread in European Vespertilionidae bats) and whose taxonomy has not been clarified. We examined fecal samples from Vespertilionidae bats (five species) captured in central Russia and found that 2/12 (16%) were positive for mastadenoviruses. The partial genome of the mastadenovirus was assembled from Pipistrellus nathusii, representing the bat adenovirus species B. The complete genome (37,915 nt) of a novel mastadenovirus was assembled from Nyctalus noctula and named BatAdV/MOW15-Nn19/Quixote. Comparative studies showed significant divergence of the Quixote genome sequence from European bat mastadenoviruses, while the only known virus showing low similarity was the isolate WA3301 from an Australian bat, and together they formed a subclade that separated from other BatAdVs. Phylogenetic and comparative analysis of the protein-coding genes provided evidence that Quixote is related to a novel species within the genus Mastadenovirus, provisionally named "K" (as the next available letter for the species). Phylogenetic analyses revealed that some earlier viruses from Western European bats, for which only partial DNA polymerase genes are known, are most likely members of the tentatively named species "K". Thus, at least two species of mastadenovirus are circulating in bats throughout Europe, from western to eastern areas.

B.1.351 SARS-CoV-2 Variant Exhibits Higher Virulence but Less Viral Shedding than That of the Ancestral Strain in Young Nonhuman Primates

We investigated the distribution, virulence, and pathogenic characteristics of mutated SARS-CoV-2 to clarify the association between virulence and the viral spreading ability of current and future circulating strains. Chinese rhesus macaques were infected with ancestral SARS-CoV-2 strain GD108 and Beta variant B.1.351 (B.1.351) and assessed for clinical signs, viral distribution, pathological changes, and pulmonary inflammation. We found that GD108 replicated more efficiently in the upper respiratory tract, whereas B.1.351 replicated more efficiently in the lower respiratory tract and lung tissue, implying a reduced viral shedding and spreading ability of B.1.351 compared with that of GD108. Importantly, B.1.351 caused more severe lung injury and dramatically elevated the level of inflammatory cytokines compared with those observed after infection with GD108. Moreover, both B.1.351 and GD108 induced spike-specific T-cell responses at an early stage of infection, with higher levels of interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α) in the B.1.351 group and higher levels of interleukin 17 (IL-17) in the GD108 group, indicating a divergent pattern in the T-cell-mediated inflammatory "cytokine storm." This study provides a basis for exploring the pathogenesis of SARS-CoV-2 variants of concern (VOCs) and establishes an applicable animal model for evaluating the efficacy and safety of vaccines and drugs. IMPORTANCE One of the priorities of the current SARS-CoV-2 vaccine and drug research strategy is to determine the changes in transmission ability, virulence, and pathogenic characteristics of SARS-CoV-2 variants. In addition, nonhuman primates (NHPs) are suitable animal models for the study of the pathogenic characteristics of SARS-CoV-2 and could contribute to the understanding of pathogenicity and transmission mechanisms. As SARS-CoV-2 variants continually emerge and the viral biological characteristics change frequently, the establishment of NHP infection models for different VOCs is urgently needed. In the study, the virulence and tissue distribution of B.1.351 and GD108 were comprehensively studied in NHPs. We concluded that the B.1.351 strain was more virulent but exhibited less viral shedding than the latter. This study provides a basis for determining the pathogenic characteristics of SARS-CoV-2 and establishes an applicable animal model for evaluating the efficacy and safety of vaccines and drugs.