Influenza A virus (IAV) infection of the respiratory tract can cause both respiratory and non-respiratory symptoms. Gastrointestinal (GI) symptoms such as diarrhea, vomiting, and abdominal pain can occur in persons with seasonal influenza A or novel IAV infections, but the extent to which IAVs can infect and replicate in GI tissues is understudied. The ongoing outbreak of A(H5N1) IAV in US dairy cattle associated with sporadic human infections has highlighted the potential public health threat posed by the introduction of infectious virus into materials that may be consumed by humans, such as milk. Here, we review epidemiologic reports documenting the frequency of GI complications in humans infected with seasonal and novel IAVs and present laboratory studies supporting the capacity of IAV to replicate in mammalian GI tissues, with an emphasis on A(H5N1) viruses. Studies assessing the ability of IAV to cause mammalian infection following consumption of virus-containing material are also presented. Collectively, these studies suggest that gastric exposure represents a potential non-respiratory route for A(H5N1) IAVs in mammals that can lead to infection and support that IAV may be detected in mammalian intestinal tissues following multiple exposure routes.

Pimodivir exerts an antiviral effect on the early stages of influenza A virus replication by inhibiting the cap-binding function of polymerase basic protein 2 (PB2). In this study, we used a combination of sequence analysis and phenotypic methods to evaluate pimodivir susceptibility of influenza A viruses collected from humans and other hosts. Screening PB2 sequences for substitutions previously associated with reduced pimodivir susceptibility revealed a very low frequency among seasonal viruses circulating in the U.S. during 2015-2020 (<0.01%; 3/11,934) and among non-seasonal viruses collected in various countries during the same period (0.2%; 18/8971). Pimodivir potently inhibited virus replication in two assays, a single-cycle HINT and a multi-cycle FRA, with IC(50) values in a nanomolar range. Median IC(50) values determined by HINT were similar for both subtypes of seasonal viruses, A (H1N1)pdm09 and A (H3N2), across three seasons. Human seasonal viruses with PB2 substitutions S324C, S324R, or N510K displayed a 27-317-fold reduced pimodivir susceptibility. In addition, pimodivir was effective at inhibiting replication of a diverse group of animal-origin viruses that have pandemic potential, including avian viruses of A (H5N6) and A (H7N9) subtypes. A rare PB2 substitution H357N was identified in an A (H4N2) subtype poultry virus that displayed >100-fold reduced pimodivir susceptibility. Our findings demonstrate a broad inhibitory activity of pimodivir and expand the existing knowledge of amino acid substitutions that can reduce susceptibility to this investigational antiviral.

We investigated unusual crow mortality in Bangladesh during January-February 2011 at two sites. Crows of two species, Corvus splendens and C. macrorhynchos, were found sick and dead during the outbreaks. In selected crow roosts, morbidity was ~1 % and mortality was ~4 % during the investigation. Highly pathogenic avian influenza virus H5N1 clade 2.3.2.1 was isolated from dead crows. All isolates were closely related to A/duck/India/02CA10/2011 (H5N1) with 99.8 % and A/crow/Bangladesh/11rs1984-15/2011 (H5N1) virus with 99 % nucleotide sequence identity in their HA genes. The phylogenetic cluster of Bangladesh viruses suggested a common ancestor with viruses found in poultry from India, Myanmar and Nepal. Histopathological changes and immunohistochemistry staining in brain, pancreas, liver, heart, kidney, bursa of Fabricius, rectum, and cloaca were consistent with influenza virus infection. Through our limited investigation in domesticated birds near the crow roosts, we did not identify any samples that tested positive for influenza virus A/H5N1. However, environmental samples collected from live-bird markets near an outbreak site during the month of the outbreaks tested very weakly positive for influenza virus A/H5N1 in clade 2.3.2.1-specific rRT-PCR. Continuation of surveillance in wild and domestic birds may identify evolution of new avian influenza virus and associated public-health risks.