Cross talk between animal and human influenza viruses

Exploring Potential Intermediates in the Cross-Species Transmission of Influenza A Virus to Humans

The influenza A virus (IAV) has been a major cause of several pandemics, underscoring the importance of elucidating its transmission dynamics. This review investigates potential intermediate hosts in the cross-species transmission of IAV to humans, focusing on the factors that facilitate zoonotic events. We evaluate the roles of various animal hosts, including pigs, galliformes, companion animals, minks, marine mammals, and other animals, in the spread of IAV to humans.

Risk Assessment of the Possible Intermediate Host Role of Pigs for Coronaviruses with a Deep Learning Predictor

Swine coronaviruses (CoVs) have been found to cause infection in humans, suggesting that Suiformes might be potential intermediate hosts in CoV transmission from their natural hosts to humans. The present study aims to establish convolutional neural network (CNN) models to predict host adaptation of swine CoVs. Decomposing of each ORF1ab and Spike sequence was performed with dinucleotide composition representation (DCR) and other traits. The relationship between CoVs from different adaptive hosts was analyzed by unsupervised learning, and CNN models based on DCR of ORF1ab and Spike were built to predict the host adaptation of swine CoVs. The rationality of the models was verified with phylogenetic analysis. Unsupervised learning showed that there is a multiple host adaptation of different swine CoVs. According to the adaptation prediction of CNN models, swine acute diarrhea syndrome CoV (SADS-CoV) and porcine epidemic diarrhea virus (PEDV) are adapted to Chiroptera, swine transmissible gastroenteritis virus (TGEV) is adapted to Carnivora, porcine hemagglutinating encephalomyelitis (PHEV) might be adapted to Primate, Rodent, and Lagomorpha, and porcine deltacoronavirus (PDCoV) might be adapted to Chiroptera, Artiodactyla, and Carnivora. In summary, the DCR trait has been confirmed to be representative for the CoV genome, and the DCR-based deep learning model works well to assess the adaptation of swine CoVs to other mammals. Suiformes might be intermediate hosts for human CoVs and other mammalian CoVs. The present study provides a novel approach to assess the risk of adaptation and transmission to humans and other mammals of swine CoVs.

Different Biophysical Properties of Cell Surface α2,3- and α2,6-Sialoglycans Revealed by Electron Paramagnetic Resonance Spectroscopic Studies

Sialoglycans on HeLa cells were labeled with a nitroxide spin radical through enzymatic glycoengineering (EGE)-mediated installation of azide-modified sialic acid (Neu5Ac9N₃) and then click reaction-based attachment of a nitroxide spin radical. α2,6-Sialyltransferase (ST) Pd2,6ST and α2,3-ST CSTII were used for EGE to install α2,6- and α2,3-linked Neu5Ac9N₃, respectively. The spin-labeled cells were analyzed by X-band continuous wave (CW) electron paramagnetic resonance (EPR) spectroscopy to gain insights into the dynamics and organizations of cell surface α2,6- and α2,3-sialoglycans. Simulations of the EPR spectra revealed average fast- and intermediate-motion components for the spin radicals in both sialoglycans. However, α2,6- and α2,3-sialoglycans in HeLa cells possess different distributions of the two components, e.g., a higher average population of the intermediate-motion component for α2,6-sialoglycans (78%) than that for α2,3-sialoglycans (53%). Thus, the average mobility of spin radicals in α2,3-sialoglycans was higher than that in α2,6-sialoglycans. Given the fact that a spin-labeled sialic acid residue attached to the 6-O-position of galactose/N-acetyl-galactosamine would experience less steric hindrance and show more flexibility than that attached to the 3-O-position, these results may reflect the differences in local crowding/packing that restrict the spin-label and sialic acid motion for α2,6-linked sialoglycans. The studies further suggest that Pd2,6ST and CSTII may have different preferences for glycan substrates in the complex environment of the extracellular matrix. The discoveries of this work are biologically important as they are useful for interpreting the different functions of α2,6- and α2,3-sialoglycans and indicate the possibility of using Pd2,6ST and CSTII to target different glycoconjugates on cells.

IL-4Rα blockade reduces influenza-associated morbidity in a murine model of allergic asthma

Background

Asthma was identified as the most common comorbidity in hospitalized patients during the 2009 H1N1 influenza pandemic. We determined using a murine model of allergic asthma whether these mice experienced increased morbidity from pandemic H1N1 (pH1N1) viral infection and whether blockade of interleukin-4 receptor α (IL-4Rα), a critical mediator of T_h2 signalling, improved their outcomes.

Methods

Male BALB/c mice were intranasally sensitized with house dust mite antigen (Der p 1) for 2 weeks; the mice were then inoculated intranasally with a single dose of pandemic H1N1 (pH1N1). The mice were administered intraperitoneally anti-IL-4Rα through either a prophylactic or a therapeutic treatment strategy.

Results

Infection with pH1N1 of mice sensitized to house dust mite (HDM) led to a 24% loss in weight by day 7 of infection (versus 14% in non-sensitized mice; p < .05). This was accompanied by increased viral load in the airways and a dampened anti-viral host responses to the infection. Treatment of HDM sensitized mice with a monoclonal antibody against IL-4Rα prior to or following pH1N1 infection prevented the excess weight loss, reduced the viral load in the lungs and ameliorated airway eosinophilia and systemic inflammation related to the pH1N1 infection.

Conclusion

Together, these data implicate allergic asthma as a significant risk factor for H1N1-related morbidity and reveal a potential therapeutic role for IL-4Rα signalling blockade in reducing the severity of influenza infection in those with allergic airway disease.

Systemic mycoses: a potential alert for complications in COVID-19 patients

As the global COVID-19 pandemic spreads worldwide, new challenges arise in the clinical landscape. The need for reliable diagnostic methods, treatments and vaccines for COVID-19 is the major worldwide urgency. While these goals are especially important, the growing risk of co-infections is a major threat not only to the health systems but also to patients' lives. Although there is still not enough published statistical data, co-infections in COVID-19 patients found that a significant number of patients hospitalized with COVID-19 developed secondary systemic mycoses that led to serious complications and even death. This review will discuss some of these important findings with the major aim to warn the population about the high risk of concomitant systemic mycoses in individuals weakened by COVID-19.

COVID-19 in Light of Seasonal Respiratory Infections

A wide diversity of zoonotic viruses that are capable of overcoming host range barriers facilitate the emergence of new potentially pandemic viruses in the human population. When faced with a new virus that is rapidly emerging in the human population, we have a limited knowledge base to work with. The pandemic invasion of the new SARS-CoV-2 virus in 2019 provided a unique possibility to quickly learn more about the pathogenesis of respiratory viruses. In this review, the impact of pandemics on the circulation of seasonal respiratory viruses is considered. The emergence of novel respiratory viruses has often been accompanied by the disappearance of existing circulating strains. Some issues arising from the spread of pandemic viruses and underlying the choices of a strategy to fight the coronavirus infection are discussed.

New Points of Departure for More Global Influenza Vaccine Use

Each year, influenza causes a significant acute respiratory disease burden. In addition, influenza pandemics periodically occur. Annual vaccination is the best tool for influenza prevention, but its effectiveness can vary from year to year. The narrow specificity of conventional vaccines and the drug resistance of currently circulating viruses reduce the effectiveness of prophylaxis and treatment and require the development of new broad-spectrum preparations. Furthermore, the challenge of creating a highly effective universal influenza vaccine takes on renewed intensity in the face of the COVID-19 pandemic.

Genetic and serologic surveillance of canine (CIV) and equine (EIV) influenza virus in Nuevo León State, México

BACKGROUND

Despite the uncontrolled distribution of the Influenza A virus through wild birds, the detection of canine influenza virus and equine influenza virus in Mexico was absent until now. Recently, outbreaks of equine and canine influenza have been reported around the world; the virus spreads quickly among animals and there is potential for zoonotic transmission.

METHODS

Amplification of the Influenza A virus matrix gene from necropsies, nasal and conjunctival swabs from trash service horses and pets/stray dogs was performed through RT-PCR. The seroprevalence was carried out through Sandwich enzyme-linked immunosorbent assay system using the M1 recombinant protein and polyclonal antibodies anti-M1.

RESULTS

The matrix gene was amplified from 13 (19.11%) nasal swabs, two (2.94%) conjunctival swabs and five (7.35%) lung necropsies, giving a total of 20 (29.41%) positive samples in a pet dog population. A total of six (75%) positive samples of equine nasal swab were amplified. Sequence analysis showed 96-99% identity with sequences of Influenza A virus matrix gene present in H1N1, H1N2 and H3N2 subtypes. The phylogenetic analysis of the sequences revealed higher identity with matrix gene sequences detected from zoonotic isolates of subtype H1N1/2009. The detection of anti-M1 antibodies in stray dogs showed a prevalence of 123 (100%) of the sampled population, whereas in horses, 114 (92.68%) positivity was obtained.

CONCLUSION

The results unveil the prevalence of Influenza A virus in the population of horses and dogs in the state of Nuevo Leon, which could indicate a possible outbreak of equine and Canine Influenza in Mexico. We suggest that the prevalence of Influenza virus in companion animals be monitored to investigate its epizootic and zoonotic potential, in addition to encouraging the regulation of vaccination in these animal species in order to improve their quality of life.

Subunit vaccines based on recombinant yeast protect against influenza A virus in a one-shot vaccination scheme

Here we report on new subunit vaccines based on recombinant yeast of the type Kluyveromyces lactis (K. lactis), which protect mice from a lethal influenza A virus infection. Applying a genetic system that enables the rapid generation of transgenic yeast, we have developed K. lactis strains that express the influenza A virus hemagglutinin, HA, either individually or in combination with the viral M1 matrix protein. Subcutaneous application of the inactivated, but otherwise non-processed yeast material shows a complete protection of BALB/c mice in prime/boost and even one-shot/single dose vaccination schemes against a subsequent, lethal challenge with the cognate influenza virus. The yeast vaccines induce titers of neutralizing antibodies that are readily comparable to those induced by an inactivated virus vaccine. These data suggest that HA and M1 are produced with a high antigenicity in the yeast cells. Based on these findings, multivalent, DIVA-capable, yeast-based subunit vaccines may be developed as promising alternatives to conventional virus-based anti-flu vaccines for veterinary applications.

Zoonotic Potential of Influenza A Viruses: A Comprehensive Overview

Influenza A viruses (IAVs) possess a great zoonotic potential as they are able to infect different avian and mammalian animal hosts, from which they can be transmitted to humans. This is based on the ability of IAV to gradually change their genome by mutation or even reassemble their genome segments during co-infection of the host cell with different IAV strains, resulting in a high genetic diversity. Variants of circulating or newly emerging IAVs continue to trigger global health threats annually for both humans and animals. Here, we provide an introduction on IAVs, highlighting the mechanisms of viral evolution, the host spectrum, and the animal/human interface. Pathogenicity determinants of IAVs in mammals, with special emphasis on newly emerging IAVs with pandemic potential, are discussed. Finally, an overview is provided on various approaches for the prevention of human IAV infections.

Serosurvey of rabies virus, canine distemper virus, parvovirus, and influenza virus in military working dogs in Korea

Rabies virus (RABV), canine distemper virus (CDV), canine parvovirus type-2 (CPV-2), and canine influenza A virus (CIV) are important contagious pathogens in canine populations. To assess post-vaccination immunity against RABV, CDV and CPV-2, and serological evidence of exposure to influenza A virus in military working dogs (MWDs) in Korea, we tested blood samples of 78 MWDs by fluorescent antibody virus neutralization (FAVN) for RABV, and by commercially available enzyme-linked immunosorbent assay (ELISA) for CDV, CPV-2, and CIV. Korean MWDs had high antibody-positive rates against RABV (97.4%, ≥0.5 IU/ml), CDV (94.8%), and CPV (100%). All dogs tested seronegative (0/78; 0%) for influenza A virus. Two 1-year-old dogs stationed in known rabies outbreak areas (Gangwon and Gyeonggi) exhibited VNA titers below the protective level (0.06 and 0.29 IU/ml, respectively). The breed and sex of MWDs were not significantly associated with antibody titers for RABV, CDV, or CPV; however, age was significantly associated with CPV antibody titers, while region of residence was associated with CDV antibody titer. Taken together, the data presented here provide important insights necessary for post-vaccination management and control of infectious diseases in MWDs.

Effects of different principles of Traditional Chinese Medicine treatment on TLR7/NF-κB signaling pathway in influenza virus infected mice

Background

Influenza virus is a single-stranded RNA virus that causes influenza in humans and animals. About 600 million people around the world suffer from influenza every year. Upon recognizing viral RNA molecules, TLR7 (Toll-like receptor) initiates corresponding immune responses. Traditional Chinese Medicines (TCMs), including Yinqiao powder, Xinjiaxiangruyin and Guizhi-and-Mahuang decoction, have been extensively applied in clinical treatment of influenza. Although the therapeutic efficacy of TCMs against influenza virus in vivo was reported previously, its underlying mechanisms are not clearly understood. This study aimed to investigate the immunological mechanisms in the treatment of influenza virus infected mice with three Chinese herbal compounds as well as the effect on TLR7/NF-κB signaling pathway during recovery.

Methods

Wild type and TLR7 KO C57BL/6 mice were infected with influenza virus FM1 and then treated with three TCMs. The physical parameters of mice (body weight and lung index) and the expression levels of components in TLR7/NF-κB signaling pathway were evaluated.

Results

After viral infection, Guizhi-and-Mahuang decoction and Yinqiao powder showed better anti-viral effect under normal condition. Compared to the viral control group, expression levels of TLR7, MyD88, IRAK4 and NF-κB were significantly reduced in all treatment groups. Furthermore, the three TCM treatment groups showed poor therapeutic efficacy and no difference in viral load compared to the viral control group in TLR7 KO mice.

Conclusion

Our study indicated that Guizhi-and-Mahuang decoction and Yinqiao powder might play a crucial role of anti-influenza virus by regulating TLR7/NF-κB signal pathway.

Serosurvey of rabies virus, canine distemper virus, parvovirus, and influenza virus in military working dogs in Korea

Rabies virus (RABV), canine distemper virus (CDV), canine parvovirus type-2 (CPV-2), and canine influenza A virus (CIV) are important contagious pathogens in canine populations. To assess post-vaccination immunity against RABV, CDV and CPV-2, and serological evidence of exposure to influenza A virus in military working dogs (MWDs) in Korea, we tested blood samples of 78 MWDs by fluorescent antibody virus neutralization (FAVN) for RABV, and by commercially available enzyme-linked immunosorbent assay (ELISA) for CDV, CPV-2, and CIV. Korean MWDs had high antibody-positive rates against RABV (97.4%, ≥0.5 IU/ml), CDV (94.8%), and CPV (100%). All dogs tested seronegative (0/78; 0%) for influenza A virus. Two 1-year-old dogs stationed in known rabies outbreak areas (Gangwon and Gyeonggi) exhibited VNA titers below the protective level (0.06 and 0.29 IU/ml, respectively). The breed and sex of MWDs were not significantly associated with antibody titers for RABV, CDV, or CPV; however, age was significantly associated with CPV antibody titers, while region of residence was associated with CDV antibody titer. Taken together, the data presented here provide important insights necessary for post-vaccination management and control of infectious diseases in MWDs.

Molecular epidemiology of swine influenza A viruses in the Southeastern United States, highlights regional differences in circulating strains

Swine influenza A virus (IAV) can cause widespread respiratory disease with high morbidity, low mortality, and have a substantial economic impact to the swine industry. Swine infection may contribute to pandemic IAV given their susceptibility to both avian and human IAVs. Currently, three IAV subtypes (H1N1, H3N2 and H1N2) circulate in swine in North America frequently combining gene segments from avian or human viruses. This study investigated the prevalence of IAV in commercial swine herds. A total of 1878 oral fluid samples were collected from pigs of all ages from 201 commercial farms located in North Carolina and South Carolina. Sixty-eight oral fluid samples from 35 farms were positive by MP gene PCR with an overall IAV-positivity of 3.6%. On the herd level, the percentage of IAV positivity was 17.4%. Fifty-six viruses were subtyped, while 12 were partly subtyped or not subtyped at all. Using de novo assembly, complete sequences were obtained for 59 HA genes. The majority of IAVs subtyped had an H1 HA demonstrating a considerable prevalence over H3 viruses. Furthermore, only six out of eleven HA types were detected which has implications for the selection of vaccines used by swine producers in the region.

Genetic analysis of a novel reassortant H11N9 Isolated from waterfowl in South Korea in 2016

Aquatic birds are known to harbor all the known influenza A viruses. In the winter of January 2016, we surveyed influenza A virus in the feces of migratory birds in South Korea. The novel re-assorted H11N9 avian influenza virus, which contains genes from avian influenza viruses of poultry and wild birds, was isolated. The polymerase basic 2 (PB2), polymerase basic 1 (PB1), hemagglutinin (HA), and nucleoprotein (NP) genes were most closely related to those of domestic duck-origin avian influenza viruses, while the non-structural (NS) gene was closely related to that of domestic goose-origin avian influenza virus. The polymerase acidic (PA), neuraminidase (NA), and matrix (M) genes were most similar to those of wild bird-origin avian influenza viruses. Our results suggested that the interaction between wild birds and domestic poultry could possibly create novel re-assorted avian influenza viruses circulating in wild birds.

Recent progress in designing inhibitors that target the drug-resistant M2 proton channels from the influenza A viruses

Influenza viruses are the causative agents for seasonal influenza, which results in thousands of deaths and millions of hospitalizations each year. Moreover, sporadic transmission of avian or swan influenza viruses to humans often leads to an influenza pandemic, as there is no preimmunity in the human body to fight against such novel strains. The metastable genome of the influenza viruses, coupled with the reassortment of different strains from a wide range of host origins, leads to the continuous evolution of the influenza virus diversity. Such characteristics of influenza viruses present a grand challenge in devising therapeutic strategies to combat influenza virus infection. This review summarizes recent progress in designing small molecule inhibitors that target the drug-resistant influenza A virus M2 proton channels and highlights the contribution of mechanistic studies of proton conductance to drug discovery. The lessons learned throughout the course of M2 drug discovery might provide insights for designing inhibitors that target other therapeutically important ion channels.

Molecular analyses of H3N2 canine influenza viruses isolated from Korea during 2013-2014

Canine influenza A virus (CIV) causes a respiratory disease among dog populations and is prevalent in North America and Asia. Recently, Asian H3N2 CIV infection has been of particular concern, with recent reports related to reassortants with pandemic 2009 strains, direct transmission from a human H3N2, a possibility of H3N2 CIV transmission to other mammals, and even the first outbreak of H3N2 CIVs in North America in April 2015. However, despite these global concerns, our understanding of how influenza A virus transmission impacts the overall populations of H3N2 CIVs remains incomplete. Hence, we investigated the evolutionary history of the most recent two Korean CIV isolates, A/canine/Korea/BD-1/2013 and A/canine/Korea/DG1/2014, along with 57 worldwide CIVs, using comprehensive molecular analyses based on genomic genotyping. This study presents that the new Korean CIV isolates are closely related to the predominantly circulating H3N2 CIVs with genotypes K, G, E, 3B, F, 2D, F, and 1E, carrying several mutations in antigenic and host determinant sites. Also, our findings show that the genome-wide genetic variations within the H3N2 CIVs are low; however, two antigenic protein (HA and NA) analysis demonstrates genetic diversification of the H3N2 CIVs, which evolves independently between Korea and China.

Multiplex RT-PCR detection of H3N2 influenza A virus in dogs

A multiplex RT-PCR (mRT-PCR) assay to detect H3N2 CIV genomic segments was developed as a rapid and cost-effective method. Its performance was evaluated with forty-six influenza A viruses from different hosts using three primer sets which amplify four segments of H3N2 CIV simultaneously. The mRT-PCR has been successful in detecting the viral segments, indicating that it can improve the speed of diagnosis for H3N2 CIV and its reassortants.

Design and testing of multiplex RT-PCR primers for the rapid detection of influenza A virus genomic segments: Application to equine influenza virus

The avian influenza A virus causes respiratory infections in animal species. It can undergo genomic recombination with newly obtained genetic material through an interspecies transmission. However, the process is an unpredictable event, making it difficult to predict the emergence of a new pandemic virus and distinguish its origin, especially when the virus is the result of multiple infections. Therefore, identifying a novel influenza is entirely dependent on sequencing its whole genome. Occasionally, however, it can be time-consuming, costly, and labor-intensive when sequencing many influenza viruses. To compensate for the difficulty, we developed a rapid, cost-effective, and simple multiplex RT-PCR to identify the viral genomic segments. As an example to evaluate its performance, H3N8 equine influenza virus (EIV) was studied for the purpose. In developing this protocol to amplify the EIV eight-segments, a series of processes, including phylogenetic analysis based on different influenza hosts, in silico analyses to estimate primer specificity, coverage, and variation scores, and investigation of host-specific amino acids, were progressively conducted to reduce or eliminate the negative factors that might affect PCR amplification. Selectively, EIV specific primers were synthesized with dual priming oligonucleotides (DPO) system to increase primer specificity. As a result, 16 primer pairs were selected to screen the dominantly circulating H3N8 EIV 8 genome segments: PA (3), PB2 (1), PA (3), NP (3), NA8 (2), HA3 (1), NS (1), and M (2). The diagnostic performance of the primers was evaluated with eight sets composing of four segment combinations using viral samples from various influenza hosts. The PCR results suggest that the multiplex RT-PCR has a wide range of applications in detection and diagnosis of newly emerging EIVs. Further, the proposed procedures of designing multiplex primers are expected to be used for detecting other animal influenza A viruses.

A novel eight amino acid insertion contributes to the hemagglutinin cleavability and the virulence of a highly pathogenic avian influenza A (H7N3) virus in mice

In 2012, an avian influenza A H7N3 (A/Mexico/InDRE7218/2012; Mx/7218) virus was responsible for two confirmed cases of human infection and led to the death or culling of more than 22 million chickens in Jalisco, Mexico. Interestingly, this virus acquired an 8-amino acid (aa)-insertion (..PENPK-DRKSRHRR-TR/GLF) near the hemagglutinin (HA) cleavage site by nonhomologous recombination with host rRNA. It remains unclear which specific residues at the cleavage site contribute to the virulence of H7N3 viruses in mammals. Using loss-of-function approaches, we generated a series of cleavage site mutant viruses by reverse genetics and characterized the viruses in vitro and in vivo. We found that the 8-aa insertion and the arginine at position P4 of the Mx/7218 HA cleavage site are essential for intracellular HA cleavage in 293T cells, but have no effect on the pH of membrane fusion. However, we identified a role for the histidine residue at P5 position in viral fusion pH. In mice, the 8-aa insertion is required for Mx/7218 virus virulence; however, the basic residues upstream of the P4 position are dispensable for virulence. Overall, our study provides the first line of evidence that the insertion in the Mx/7218 virus HA cleavage site confers its intracellular cleavability, and consequently contributes to enhanced virulence in mice.

Molecular epidemiology study of swine influenza virus revealing a reassorted virus H1N1 in swine farms in Cuba

In this report, we describe the emergence of reassorted H1N1 swine influenza virus, originated from a reassortment event between the H1N1 pandemic influenza virus (H1N1p/2009) and endemic swine influenza virus in Cuban swine population. In November 2010, a clinical respiratory outbreak was reported on a pig fattening farm in Cuba. Phylogenetic analysis showed that all the genes of one of the isolate obtained, with the exception of neuraminidase, belonged to the H1N1p/2009 cluster. This finding suggests that H1N1pdm has been established in swine and has become a reservoir of reassortment that may produce new viruses with both animal and public health risks.

Efficient isolation of Swine influenza viruses by age-targeted specimen collection

The control of swine influenza virus (SIV) infection is paramount for increasing the productivity of pig farming and minimizing the threat of pandemic outbreaks. Thus, SIV surveillance should be conducted by region and on a regular basis. Here, we established a microneutralization assay specific for SIV seroprevalence surveillance by using reporter gene-expressing recombinant influenza viruses. Growth-based SIV seroprevalence revealed that most sows and piglets were positive for neutralizing antibodies against influenza viruses. In contrast, the 90-day-old growing pigs exhibited limited neutralizing activity in their sera, suggesting that this particular age of population is most susceptible to SIV infection and thus is an ideal age group for SIV isolation. From nasal swab specimens of healthy pigs in this age population, we were able to isolate SIVs at a higher incidence (5.3%) than those of previous reports. Nucleotide sequencing and phylogenetic analysis of the hemagglutinin (HA) genes revealed that the isolated SIVs have circulated and evolved in pigs but not have been recently introduced from humans, implying that a large number of SIV lineages may remain "undiscovered" in the global porcine populations. We propose that the 90-day-old growing pig-targeted nasal swab collection presented in this study facilitates global SIV surveillance and contributes to the detection and control of SIV infection.

A review of infection control in community healthcare: new challenges but old foes

The demographics of the healthcare population are changing, with an ever-greater proportion of people being treated outside the traditional hospital setting through community healthcare. This shift in the way that healthcare is delivered raises new concerns over community healthcare-associated infections (HCAIs). A literature search between 2000 and December 2013 was conducted in databases including PubMed, SciVerse ScienceDirect and Google Scholar. National and international guideline and policy documents were searched using Google. Many terms were used in the literature searches, including ‘nosocomial’, ‘healthcare infection’, ‘community’ and ‘nursing home’. The rates of HCAI in community healthcare are similar to the rates found in the acute hospital setting, but the types of infection differ, with a greater focus on urinary tract infections (UTIs) in the community and ventilator-associated pneumonias in the hospital setting. Patients who acquire a community HCAI are more likely to exhibit reduced physical condition, have increased levels of morbidity and have higher mortality rates than individuals without infection. Infection control programmes have been developed worldwide to reduce the rates of hospital HCAIs. Such interventions are equally as valid in the community, but how best to implement them and their subsequent impact are much less well understood. The future is clear: HCAIs in the community are going to become an ever-increasing burden and it is critical that our approach to these infections is brought quickly in line with present hospital sector standards.

Influenza A penetrates host mucus by cleaving sialic acids with neuraminidase

Background

Influenza A virus (IAV) neuraminidase (NA) cleaves sialic acids (Sias) from glycans. Inhibiting NA with oseltamivir suppresses both viral infection, and viral release from cultured human airway epithelial cells. The role of NA in viral exit is well established: it releases budding virions by cleaving Sias from glycoconjugates on infected cells and progeny virions. The role of NA in viral entry remains unclear. Host respiratory epithelia secrete a mucus layer rich in heavily sialylated glycoproteins; these could inhibit viral entry by mimicking sialylated receptors on the cell surface. It has been suggested that NA allows influenza to penetrate the mucus by cleaving these sialylated decoys, but the exact mechanism is not yet established.

Methods

We tested IAV interaction with secreted mucus using frozen human trachea/bronchus tissue sections, and bead-bound purified human salivary mucins (HSM) and purified porcine submaxillary mucins (PSM). The protective effect of mucus was analyzed using MDCK cells coated with purified HSM and PSM with known Sia content. Oseltamivir was used to inhibit NA activity, and the fluorescent reporter substrate, 4MU-Neu5Ac, was used to quantify NA activity.

Results

IAV binds to the secreted mucus layer of frozen human trachea/bronchus tissues in a Sia dependent manner. HSM inhibition of IAV infection is Sia dose-dependent, but PSM cannot inhibit infection of underlying cells. HSM competitively inhibits NA cleavage of 4MU-Neu5Ac, reporter substrate. Human IAV effectively cleaves Sias from HSM but not from PSM, and binds to HSM but not to PSM.

Conclusion

IAV interacts with human mucus on frozen tissue sections and mucus-coated beads. Inhibition of IAV infection by sialylated human mucus is dose-dependent, and enhanced when NA is inhibited with oseltamivir. Thus NA cleaves sialylated decoys during initial stages of infection. Understanding IAV interactions with host mucins is a promising new avenue for drug development.