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Background Human spillovers of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to dogs and the emergence of a highly contagious avian-origin H3N2 canine influenza virus have raised concerns on the role of dogs in the spread of SARS-CoV-2 and their susceptibility to existing human and avian influenza viruses, which might result in further reassortment. Methods We systematically studied the replication kinetics of SARS-CoV-2, SARS-CoV, influenza A viruses of H1, H3, H5, H7, and H9 subtypes, and influenza B viruses of Yamagata-like and Victoria-like lineages in ex vivo canine nasal cavity, soft palate, trachea, and lung tissue explant cultures and examined ACE2 and sialic acid (SA) receptor distribution in these tissues. Results There was limited productive replication of SARS-CoV-2 in canine nasal cavity and SARS-CoV in canine nasal cavity, soft palate, and lung, with unexpectedly high ACE2 levels in canine nasal cavity and soft palate. Canine tissues were susceptible to a wide range of human and avian influenza viruses, which matched with the abundance of both human and avian SA receptors. Conclusions Existence of suitable receptors and tropism for the same tissue foster virus adaptation and reassortment. Continuous surveillance in dog populations should be conducted given the many chances for spillover during outbreaks.

Background. Previous studies have established that antibody titer measured by the hemagglutination-inhibiting (HAI) assay is correlated with protection against influenza virus infection, with an HAI titer of 1:40 generally associated with 50% protection. Methods. We recruited index cases with confirmed influenza virus infection from outpatient clinics, and followed up their household contacts for 7–10 days to identify secondary infections. Serum samples collected from a subset of household contacts were tested by HAI and microneutralization (MN) assays against prevalent influenza viruses. We analyzed the data using an individual hazard-based transmission model that adjusted for age and vaccination history. Results. Compared to a reference group with antibody titers

Highly pathogenic avian influenza H5N1 viruses cause severe disease in humans, and dysregulation of cytokine responses is believed to contribute to the pathogenesis of human H5N1 disease. However, mechanisms leading to the increased induction of proinflammatory cytokines by H5N1 viruses are poorly understood. We show that the innate sensing receptor RIG-I is involved in interferon regulatory factor 3 (IRF3), NF-κB nuclear translocation, p38 activation, and the subsequent interferon (IFN) β, IFN-λ1, and tumor necrosis factor α induction during H5N1 infection. Soluble mediators from H5N1-infected human macrophages upregulate RIG-I, MDA5, and TLR3 to much higher levels than those from seasonal H1N1 in uninfected human macrophages and alveolar epithelial cells via paracrine IFNAR1/JAK but not IFN-λ receptor signaling. Compared with H1N1 virus-induced mediators, H5N1 mediators markedly enhance the cytokine response to PolyIC and to both seasonal and H5N1 virus infection in a RIG-I-dependent manner. Thus, sensitizing neighboring cells by upregulation of RIG-I contributes to the amplified cytokine cascades during H5N1 infection.

Human disease caused by highly pathogenic avian influenza (H5N1) is associated with fulminant viral pneumonia and mortality rates in excess of 60%. Cytokine dysregulation is thought to contribute to its pathogenesis. In comparison with human seasonal influenza (H1N1) viruses, clade 1, 2.1, and 2.2 H5N1 viruses induced higher levels of tumor necrosis factor-alpha in primary human macrophages. To understand viral genetic determinants responsible for this hyperinduction of cytokines, we constructed recombinant viruses containing different combinations of genes from high-cytokine (A/Vietnam/1203/04) and low-cytokine (A/WSN/33) phenotype H1N1 viruses and tested their cytokine-inducing phenotype in human macrophages. Our results suggest that the H5N1 polymerase gene segments, and to a lesser extent the NS gene segment, contribute to cytokine hyperinduction in human macrophages and that a putative H5 pandemic virus that may arise through genetic reassortment between H5N1 and one of the current seasonal influenza viruses may have a markedly altered cytokine phenotype.

In an observational study of 582 patients with laboratory-confirmed influenza virus infections and their household contacts, we found that the initiation of oseltamivir within 24 hours was associated with shorter duration of self-reported illness symptoms (56% reduction in duration; 95% confidence interval, 41%-67%). However, we did not find any association of oseltamivir treatment with duration of viral shedding by polymerase chain reaction or with the risk of household transmission.