Influenza infection in humans and pigs in southeastern China

Human Immunity and Susceptibility to Influenza A(H3) Viruses of Avian, Equine, and Swine Origin

Influenza A viruses (IAVs) of subtype H3 that infect humans are antigenically divergent from those of birds, horses, and swine. Human immunity against these viruses might be limited, implying potential pandemic risk. To determine human risk, we selected 4 avian, 1 equine, and 3 swine IAVs representing major H3 lineages. We tested serum collected during 2017-2018 from 286 persons in Belgium for hemagglutination inhibiting antibodies and virus neutralizing antibodies against those animal-origin IAVs and tested replication in human airway epithelia. Seroprevalence rates for circulating IAVs from swine in North America were >51%, swine in Europe 7%-37%, and birds and equids ≤12%. Replication was efficient for cluster IV-A IAVs from swine in North America and IAVs from swine in Europe, intermediate for IAVs from horses and poultry, and absent for IAVs from wild birds and a novel human-like swine IAV in North America. Public health risk may be highest for swine H3 IAVs.

Mathematical Modeling to Predict COVID-19 Infection and Vaccination Trends

Background: COVID-19 caused by the Severe Acute Respiratory Syndrome Coronavirus 2 placed the health systems around the entire world in a battle against the clock. While most of the existing studies aimed at forecasting the infections trends, our study focuses on vaccination trend(s). Material and methods: Based on these considerations, we used standard analyses and ARIMA modeling to predict possible scenarios in Romania, the second-lowest country regarding vaccinations from the entire European Union. Results: With approximately 16 million doses of vaccine against COVID-19 administered, 7,791,250 individuals had completed the vaccination scheme. From the total, 5,058,908 choose Pfizer−BioNTech, 399,327 Moderna, 419,037 AstraZeneca, and 1,913,978 Johnson & Johnson. With a cumulative 2147 local and 17,542 general adverse reactions, the most numerous were reported in recipients of Pfizer−BioNTech (1581 vs. 8451), followed by AstraZeneca (138 vs. 6033), Moderna (332 vs. 1936), and Johnson & Johnson (96 vs. 1122). On three distinct occasions have been reported >50,000 individuals who received the first or second dose of a vaccine and >30,000 of a booster dose in a single day. Due to high reactogenicity in case of AZD1222, and time of launching between the Pfizer−BioNTech and Moderna vaccine could be explained differences in terms doses administered. Furthermore, ARIMA(1,1,0), ARIMA(1,1,1), ARIMA(0,2,0), ARIMA(2,1,0), ARIMA(1,2,2), ARI-MA(2,2,2), ARIMA(0,2,2), ARIMA(2,2,2), ARIMA(1,1,2), ARIMA(2,2,2), ARIMA(2,1,1), ARIMA(2,2,1), and ARIMA (2,0,2) for all twelve months and in total fitted the best models. These were regarded according to the lowest MAPE, p-value (p < 0.05, p < 0.01, and p < 0.001) and through the Ljung−Box test (p < 0.05, p < 0.01, and p < 0.001) for autocorrelations. Conclusions: Statistical modeling and mathematical analyses are suitable not only for forecasting the infection trends but the course of a vaccination rate as well.

Evidence for Cross-species Influenza A Virus Transmission Within Swine Farms, China: A One Health, Prospective Cohort Study

Background

Our understanding of influenza A virus transmission between humans and pigs is limited.

Methods

Beginning in 2015, we used a One Health approach and serial sampling to prospectively study 299 swine workers and 100 controls, their 9000 pigs, and 6 pig farm environments in China for influenza A viruses (IAVs) using molecular, culture, and immunological techniques. Study participants were closely monitored for influenza-like illness (ILI) events.

Results

Upon enrollment, swine workers had higher serum neutralizing antibody titers against swine H1N1 and higher nasal wash total immunoglobulin A (IgA) and specific IgA titers against swine H1N1 and H3N2 viruses. Over a period of 12 months, IAVs were detected by quantitative reverse-transcription polymerase chain reaction in 46 of 396 (11.6%) environmental swabs, 235 of 3300 (7.1%) pig oral secretion, 23 of 396 (5.8%) water, 20 of 396 (5.1%) aerosol, and 19 of 396 (4.8%) fecal-slurry specimens. Five of 32 (15.6%) participants with ILI events had nasopharyngeal swab specimens that were positive for IAV, and 17 (53.1%) demonstrated 4-fold rises in neutralization titers against a swine virus. Reassorted Eurasian avian-lineage H1N1, A(H1N1)pdm09-like, and swine-lineage H3N2 viruses were identified in pig farms. The A(H1N1)pdm09-like H1N1 viruses identified in swine were nearly genetically identical to the human H1N1 viruses isolated from the participants with ILI.

Conclusions

There was considerable evidence of A(H1N1)pdm09-like, swine-lineage H1N1, and swine-lineage H3N2 viruses circulating, likely reassorting, and likely crossing species within the pig farms. These data suggest that stronger surveillance for novel influenza virus emergence within swine farms is imperative.

Nanovaccine Confers Dual Protection Against Influenza A Virus And Porcine Circovirus Type 2

BACKGROUND

The influenza A virus (IAV) is known for its high variability and poses a huge threat to the health of humans and animals. Pigs play a central role in the cross-species reassortment of IAV. Ectodomain of matrix protein 2 (M2e) is the most conserved protective antigen in IAV and can be used to develop nanovaccines through nanoparticles displaying to increase its immunogenicity. However, the high immunogenicity of nanoparticles can cause the risk of off-target immune response, and excess unwanted antibodies may interfere with the protective efficacy of M2e-specific antibodies. Therefore, it is necessary to select reasonable nanoparticles to make full use of antibodies against nanoparticles while increasing the level of M2e-specific antibodies. Porcine circovirus type 2 (PCV2) is the most susceptible virus in pigs and can promote IAV infection. It is meaningful to develop a vaccine that can simultaneously control swine influenza virus (SIV) and PCV2.

METHODS

In the present study, M2e of different copy numbers were inserted into the capsid (Cap) protein of PCV2 and expressed in Escherichia coli to form self-assembled chimeric virus-like particles (VLPs) nanovaccine. BALB/c mice and pigs were immunized with these nanovaccines to explore optimal anti-IAV and anti-PCV2 immunity.

RESULTS

Cap is capable of carrying at least 81 amino acid residues (three copies of M2e) at its C-terminal without impairing VLPs formation. Cap-3M2e VLPs induced the highest levels of M2e-specific immune responses, conferring protection against lethal challenge of IAVs from different species and induced specific immune responses consistent with PCV2 commercial vaccines in mice. In addition, Cap-3M2e VLPs induced high levels of M2e-specific antibodies and PCV2-specific neutralizing antibodies in pigs.

CONCLUSION

Cap-3M2e VLP is an economical and promising bivalent nanovaccine, which provides dual protection against IAV and PCV2.

Weighing serological evidence of human exposure to animal influenza viruses - a literature review

Assessing influenza A virus strains circulating in animals and their potential to cross the species barrier and cause human infections is important to improve human influenza surveillance and preparedness. We reviewed studies describing serological evidence of human exposure to animal influenza viruses. Comparing serological data is difficult due to a lack of standardisation in study designs and in laboratory methods used in published reports. Therefore, we designed a scoring system to assess and weigh specificity of obtained serology results in the selected articles. Many studies report reliable evidence of antibodies to swine influenza viruses among persons occupationally exposed to pigs. Most avian influenza studies target H5, H7 and H9 subtypes and most serological evidence of human exposure to avian influenza viruses is reported for these subtypes. Avian influenza studies receiving a low grade in this review often reported higher seroprevalences in humans compared with studies with a high grade. Official surveillance systems mainly focus on avian H5 and H7 viruses. Swine influenza viruses and avian subtypes other than H5 and H7 (emphasising H9) should be additionally included in official surveillance systems. Surveillance efforts should also be directed towards understudied geographical areas, such as Africa and South America.

Increased risk of A(H1N1)pdm09 influenza infection in UK pig industry workers compared to a general population cohort

BACKGROUND

Pigs are mixing vessels for influenza viral reassortment, but the extent of influenza transmission between swine and humans is not well understood.

OBJECTIVES

To assess whether occupational exposure to pigs is a risk factor for human infection with human and swine-adapted influenza viruses.

METHODS

UK pig industry workers were frequency-matched on age, region, sampling month, and gender with a community-based comparison group from the Flu Watch study. HI assays quantified antibodies for swine and human A(H1) and A(H3) influenza viruses (titres ≥ 40 considered seropositive and indicative of infection). Virus-specific associations between seropositivity and occupational pig exposure were examined using multivariable regression models adjusted for vaccination. Pigs on the same farms were also tested for seropositivity.

RESULTS

Forty-two percent of pigs were seropositive to A(H1N1)pdm09. Pig industry workers showed evidence of increased odds of A(H1N1)pdm09 seropositivity compared to the comparison group, albeit with wide confidence intervals (CIs), adjusted odds ratio after accounting for possible cross-reactivity with other swine A(H1) viruses (aOR) 25·3, 95% CI (1·4-536·3), P = 0·028.

CONCLUSION

The results indicate that A(H1N1)pdm09 virus was common in UK pigs during the pandemic and subsequent period of human A(H1N1)pdm09 circulation, and occupational exposure to pigs was a risk factor for human infection. Influenza immunisation of pig industry workers may reduce transmission and the potential for virus reassortment.

Characterization of a novel reassortant influenza A virus (H2N2) from a domestic duck in Eastern China

While H2N2 viruses have been sporadically isolated from wild and domestic birds, H2N2 viruses have not been detected among human populations since 1968. Should H2N2 viruses adapt to domestic poultry they may pose a risk of infection to people, as most anyone born after 1968 would likely be susceptible to their infection. We report the isolation of a novel influenza A virus (H2N2) cultured in 2013 from a healthy domestic duck at a live poultry market in Wuxi City, China. Sequence data revealed that the novel H2N2 virus was similar to Eurasian avian lineage avian influenza viruses, the virus had been circulating for ≥ two years among poultry, had an increase in α2,6 binding affinity, and was not highly pathogenic. Approximately 9% of 100 healthy chickens sampled from the same area had elevated antibodies against the H2 antigen. Fortunately, there was sparse serological evidence that the virus was infecting poultry workers or had adapted to infect other mammals. These findings suggest that a novel H2N2 virus has been circulating among domestic poultry in Wuxi City, China and has some has increased human receptor affinity. It seems wise to conduct better surveillance for novel influenza viruses at Chinese live bird markets.

Review: molecular evolution and the feasibility of an avian influenza virus becoming a pandemic strain--a conceptual shift

During recent years, a conceptual shift took place with respect to the genetic dynamics of influenza A viruses. In difference of the widely accepted approach that avian viral strains have the capacity to infect man only after undergoing genetic reassortment within pigs, it is now contended that direct transfection of man by intact avian-harbored viral genotypes is an actual, recurrent move, which may bring bout the generation of a new pandemic strain. This cardinal conceptual shift has been propelled by the appearance in 1997 of the zoonotic avian influenza H5N1 virus--a virulent, not yet contagious strain for humans--and ostensibly followed a genuine, unprecedented path within the evolutionary paradigm of Influenza A virus. This paper suggests that direct avian-human genetic interface is a pristine fundamental within the natural history of this protean pathogen, points at earlier as well as corroborative findings leading to such postulation, and regards the course of the H5N1 virus (and alike), as a readily detectable and traceable one, presently, rather then a novel development It further examines the general feasibility of various components of that interface at large, such that give rise--whether gradually or abruptly--to pandemic genotypes, in terms of infectivity, pathogenicity and contagiousness. Within that context, the anticipated involvement of certain human-adapted antigenic subtypes is referred to, extrapolatively. Connectedly, the significance of natural ice as plausible regenerator of influenza A viruses, and its possible contribution to the emergence and reemergence of pandemic strains are accentuated.

Measurement of antibodies to avian influenza virus A(H7N7) in humans by hemagglutination inhibition test

During the epizootic of highly pathogenic avian influenza A(H7N7) in 2003 in The Netherlands, RT-PCR and culture confirmed infection was detected in 89 persons who were ill. A modified hemagglutination inhibition (HI) test using horse erythrocytes and 2 hemagglutinating units of virus was applied to assess retrospectively the extent of human (subclinical) infection. Validation of the HI-test with sera from 34 RT-PCR and culture confirmed A(H7) infected persons and sera from 100 persons from a human influenza vaccine trial in autumn 2002 showed that this HI-test had a sensitivity of 85% and a specificity of 100% when using a cut-off titer of > or =10. Using this cut-off value, A(H7) specific antibodies were detected in 49% of 508 persons exposed to poultry and in 64% of 63 persons exposed to A(H7) infected persons. Correlation of seropositivity with the occurrence of eye symptoms in exposed persons who had not received antiviral prophylaxis and of reduced seropositivity with taking antiviral prophylaxis provided further evidence that the A(H7) HI antibody titers were real. In conclusion, by applying an HI-test using horse erythrocytes human antibodies against the avian A(H7N7) virus were detected with high sensitivity and specificity in an unexpectedly high proportion of exposed persons.

Serologic evidence of human and swine influenza in Mayan persons

Antibodies against influenza viruses were detected in 115 serum samples from indigenous Mayan persons from Kochol, Yucatán. Seropositivity rates were 26.9% to A/Bayern/7/95, 40.8% to A/Sydney/5/97, 1.7% to A/Swine/Wisconsin/238/97, and 79.1% to A/Swine/Minnesota/593/99. This report is the first in Mexico of the prevalence of antibodies to swine influenza virus in humans.

Genetic subtyping of influenza A viruses using RT-PCR with a single set of primers based on conserved sequences within the HA2 coding region

Influenza A viruses are subtyped conventionally according to the antigenic characteristics of the external glycoproteins, haemagglutinin (HA) and neuraminidase (NA). To date 15 HA and 9 NA subtypes have been described. There is a need to develop fast, accurate and reliable methods to identify influenza virus subtypes, which may be associated with disease outbreaks. An RT-PCR is described using a single primer pair based on a conserved region of the HA2 gene that can detect all 15 HA influenza A subtypes. The assay was validated initially using a panel of 12 known standard prototype strains of influenza virus representing 6 HA subtypes and subsequently in a blind study using a panel of 30 strains. Selected viruses represented all known HA subtypes derived from avian, swine and human hosts separated both geographically and with time Sequence analysis of RT-PCR product showed complete correlation with results obtained using conventional serological methods. It is concluded that this RT-PCR is a reliable, robust and reproducible tool for the rapid identification of a wide range of all the HA subtypes of influenza A viruses.

Seroepidemiological evidence of avian H4, H5, and H9 influenza A virus transmission to pigs in southeastern China

Pig serum samples collected in southeastern China were examined for antibodies to influenza A viruses. Since the hemagglutination inhibition (HI) test does not accurately detect antibodies to the hemagglutinins (HAs) of "avian" influenza viruses, we utilized the neutralization (NT) test to detect subtype-specific antibodies to the HA of avian viruses in pig sera. Neutralizing antibodies to H1, H3, H4, and H5 influenza viruses were detected in the serum samples collected in 1977-1982 and 1998, suggesting that pigs in China have been sporadically infected with avian H4 and H5 viruses in addition to swine and human H1 and H3 viruses. Antibodies to H9 virus, on the other hand, were found only in the sera collected in 1998, not in those collected in 1977-1982, correlating with the recent spread in poultry and subsequent isolation of H9N2 viruses from pigs and humans in 1998. The present results indicate that avian influenza viruses have been transmitted to pig populations in southeastern China.

Identification and subtyping of avian influenza viruses by reverse transcription-PCR

Avian influenza viruses have 15 different hemagglutinin (HA) subtypes (H1-H15). We report a procedure for the identification and HA-subtyping of avian influenza virus by reverse transcription-PCR (RT-PCR). The avian influenza virus is identified by RT-PCR using a set of primers specific to the nucleoprotein (NP) gene of avian influenza virus. The HA-subtypes of avian influenza virus were determined by running simultaneously 15 RT-PCR reactions, each using a set of primers specific to one HA-subtype. For a single virus strain or isolate, only one of the 15 RT-PCR reactions will give a product of expected size, and thus the HA-subtype of the virus is determined. The result of HA-subtyping was then confirmed by sequence analysis of the PCR product. A total of 80 strains or isolates of avian influenza viruses were subtyped by this RT-PCR procedure, and the result of RT-PCR gave an excellent (100%) correlation with the result of the conventional serological method. The RT-PCR procedure we developed is rapid and sensitive, and could be used for the identification and HA-subtyping of avian influenza virus in organ homogenates.

Characterization of H5N2 influenza viruses from Italian poultry

From October 1997 to January 1998, highly pathogenic H5N2 avian influenza viruses caused eight outbreaks of avian influenza in northern Italy. A nonpathogenic H5N9 influenza virus was also isolated during the outbreaks as a result of virological and epidemiological surveillance to control the spread of avian influenza to neighbouring regions. Antigenic analysis showed that the Italian H5N2 isolates were antigenically similar to, although distinguishable from, A/HK/156/97, a human influenza H5N1 virus isolated in Hong Kong in 1997. Phylogenetic analysis of the haemagglutinin (HA) genes showed that the highly pathogenic Italian viruses clustered with the Hong Kong strains, whereas the nonpathogenic H5N9 virus, despite its epidemiological association with the highly pathogenic Italian isolates, was most closely related to the highly pathogenic A/Turkey/England/91 (H5N1) strain. Like the HA phylogenetic tree, the nonstructural (NS) phylogenetic tree showed that the H5N2 Italian virus genes are clearly separate from those of the H5N9 strain. In contrast, results of the phylogenetic analysis of nucleoprotein (NP) genes indicated a closer genetic relationship between the two Italian virus groups, a finding suggesting a common progenitor. Comparison of the HA, NS and NP genes of the Italian H5 strains with those of the H5N1 viruses simultaneously circulating in Hong Kong revealed that the two groups of viruses do not share a recent common ancestor. No virological and serological evidence of bird-to-human transmission of the Italian H5N2 influenza viruses was found.

DNA vaccination against influenza viruses: a review with emphasis on equine and swine influenza

The influenza virus vaccines that are commercially-available for humans, horses and pigs in the United States are inactivated, whole-virus or subunit vaccines. While these vaccines may decrease the incidence and severity of clinical disease, they do not consistently provide complete protection from virus infection. DNA vaccines are a novel alternative to conventional vaccination strategies, and offer many of the potential benefits of live virus vaccines without their risks. In particular, because immunogens are synthesized de novo within DNA transfected cells, antigen can be presented by MHC class I and II molecules, resulting in stimulation of both humoral and cellular immune responses. Influenza virus has been used extensively as a model pathogen in DNA vaccine studies in mice, chickens, ferrets, pigs, horses and non-human primates, and clinical trials of DNA-based influenza virus vaccines are underway in humans. Our studies have focused on gene gun delivery of DNA vaccines against equine and swine influenza viruses in mice, ponies and pigs, including studies employing co-administration of interleukin-6 DNA as an approach for modulating and adjuvanting influenza virus hemagglutinin-specific immune responses. The results indicate that gene gun administration of plasmids encoding hemagglutinin genes from influenza viruses is an effective method for priming and/or inducing virus-specific immune responses, and for providing partial to complete protection from challenge infection in mice, horses and pigs. In addition, studies of interleukin-6 DNA co-administration in mice clearly demonstrate the potential for this approach to enhance vaccine efficacy and protection.

Influenza and respiratory syncytial virus. Update on infection, management, and prevention

This article is an overview of the epidemiology and spectrum of clinical disease attributed to influenza and respiratory syncytial virus in children. It separately discusses the pathogenesis of the two diseases and the host responses to the viruses to emphasize each infection's significance and need for a vaccine. Updates on current preventive measures and a preview of potential future vaccine developments are presented.

Baculovirus-derived hemagglutinin vaccines protect against lethal influenza infections by avian H5 and H7 subtypes

Baculoviruses were engineered to express hemagglutinin (HA) genes of recent avian influenza (AI) isolates of the H5 and H7 subtypes. The proteins were expressed as either intact (H7) or slightly truncated versions (H5). In both cases purified HA proteins from insect cell cultures retained hemagglutination activity and formed rosettes in solution, indicating proper folding. Although immunogenic in this form, these proteins were more effective when administered subcutaneously in a water-in-oil emulsion. One or two-day-old specific pathogen free (SPF) White Rock chickens, free of maternal AI antibodies, responded with variable serum HI titers, but in some cases the titers were comparable to those achieved using whole virus preparations. Vaccination of three-week-old chickens with 1.0 microg of protein per bird generated a more consistent serum antibody response with an average geometric mean titer (GMT) of 121 (H5) and 293 (H7) at 21 days postvaccination. When challenged with highly pathogenic strains of the corresponding AI subtypes, the vaccinated birds were completely protected against lethal infection and in some cases exhibited reduced or no cloacal shedding at 3 days postinfection. Vaccine protocols employing these recombinant HA proteins will not elicit an immune response against internal AI proteins and thus will not interfere with epidemiological surveys of natural influenza infections in the field.

Rapid evolution of H5N1 influenza viruses in chickens in Hong Kong

The H5N1 avian influenza virus that killed 6 of 18 persons infected in Hong Kong in 1997 was transmitted directly from poultry to humans. Viral isolates from this outbreak may provide molecular clues to zoonotic transfer. Here we demonstrate that the H5N1 viruses circulating in poultry comprised two distinguishable phylogenetic lineages in all genes that were in very rapid evolution. When introduced into new hosts, influenza viruses usually undergo rapid alteration of their surface glycoproteins, especially in the hemagglutinin (HA). Surprisingly, these H5N1 isolates had a large proportion of amino acid changes in all gene products except in the HA. These viruses maybe reassortants each of whose HA gene is well adapted to domestic poultry while the rest of the genome arises from a different source. The consensus amino acid sequences of "internal" virion proteins reveal amino acids previously found in human strains. These human-specific amino acids may be important factors in zoonotic transmission.

Defining appropriate health status and management programs for specific-pathogen-free swine for xenotransplantation

Swine are expected to be utilized as xenograft donors for both whole-organ and cellular transplantation. In order to meet the criteria for regulatory guidelines, donor animals are going to have to be free of potential zoonoses and other complicating diseases. Screening of animals will have to include tests for viruses, bacteria, parasites, congenital defects, and other inapparent diseases such as neoplasia or metabolic dysfunctions. The term Specific-Pathogen-Free (SPF) swine is a proprietary designation in the U.S. that does not include screening for all appropriate organisms for xenotransplantation. A program for breeding animals as xenograft donors will have to be conducted in a biomedical research facility rather than a conventional farm setting. The research programs at such a facility should include serology, microbiology, necropsy, histology and parasitology. The use of sentinel animal monitoring in a research facility is one method to ensure compliance. It will be impossible to provide complete individual animal screening in a timely fashion prior to performing a xenograft transplant. Quality control measures need to ensure that there is a reasonable confidence that the donor tissue is appropriate for the procedure to be performed. It is suggested that a term such as xenograft-defined flora be used to designate the appropriate health status of donor animals rather than SPF in order to avoid confusion with existing standards.