Varying Viral Replication and Disease Profiles of H2N2 Influenza in Ferrets Is Associated with Virus Isolate and Inoculation Route.

H2N2 influenza virus, the causative agent of the 1957 "Asian flu" pandemic, has disappeared from circulation. However, H2-influenza viruses are still circulating in avian reservoirs. Combined with the waning of H2N2-specific immunity in the human population, there is a risk of reintroduction of H2N2 influenza virus. Vaccines could help in preventing a future pandemic, but to assess their efficacy animal models are required. We therefore set out to expand the ferret model for H2N2 influenza disease by infecting ferrets intranasally or intratracheally with four different H2N2 viruses to investigate their influence on the severity of disease. The H2N2 viruses were collected either during the pandemic or near the end of H2N2 circulation and covered both clade I and clade II viruses. Infection of ferrets with the different viruses showed that viral replication, disease, and pathology differed markedly between virus isolates and infection routes. Intranasal inoculation induced a severe to mild rhinitis, depending on the virus isolate, and did not lead to lung infection or pathology. When administered intratracheally, isolates that successfully replicated in the lower respiratory tract (LRT) induced a nonlethal disease that resembles that of a moderate pneumonia in humans. Differences in viral replication and disease between viruses could be associated with their binding preference for α2,3- and α2,6-sialic acid. The model presented here could facilitate the development of a new generation of H2N2 influenza vaccines. IMPORTANCE In 1957 the world was subjected to a pandemic caused by an influenza A virus of the subtype H2N2. Although the virus disappeared in 1968, H2 viruses continue to circulate in avian reservoirs. It is therefore possible that the H2N2 influenza virus will be reintroduced into the human population, which can lead to another pandemic. The impact of a new H2N2 influenza pandemic can be mitigated by vaccination. However, these vaccines first need to be developed and tested in animal models. In preparation for this, we expanded the ferret model to mimic the different facets of human H2N2 influenza infection and disease. This model can be used for the development and evaluation of new H2N2 influenza vaccines.

The pathogenicity and transmission of live bird market H2N2 avian influenza viruses in chickens, Pekin ducks, and guinea fowl.

H2N2 subtype low pathogenic avian influenza viruses (LPAIVs) have persisted in live bird markets (LBMs) in the Northeastern United States since 2014. Although unrelated to the 1957 pandemic H2N2 lineage, there is concern that the virus could have animal and public health consequences because of high contact with humans and numerous species in the LBM system. The pathogenicity, infectivity, and transmissibility of six LBM H2N2 viruses isolated from three avian species in LBMs were examined in chickens. Two of these isolates were also tested in Pekin ducks and guinea fowl. Full genome sequence was obtained from all 6 isolates and evaluated for genetic markers for host adaptation and pathogenicity in poultry. Clinical signs were not observed in any host with any of the isolates, however one recent isolate was shed at higher titers than the other isolates and had the lowest bird infectious dose of all the isolates tested in all three species. This isolate, A/chicken/NY/19-012787-1/2019, was also the only isolate with a deletion in the stalk region of the neuraminidase protein (NA). This supports the theory that the NA stalk deletion is evidence of adaptation to gallinaceous poultry.

Systemic and respiratory T-cells induced by seasonal H1N1 influenza protect against pandemic H2N2 in ferrets.

Traditional influenza vaccines primarily induce a narrow antibody response that offers no protection against heterosubtypic infections. Murine studies have shown that T cells can protect against a broad range of influenza strains. However, ferrets are a more potent model for studying immune correlates of protection in influenza infection. We therefore set out to investigate the role of systemic and respiratory T cells in the protection against heterosubtypic influenza A infections in ferrets. H1N1-priming induced systemic and respiratory T cells that responded against pandemic H2N2 and correlated with reduced viral replication and disease. CD8-positive T cell responses in the upper and lower respiratory tract were exceptionally high. We additionally confirmed that H2N2-responsive T cells are present in healthy human blood donors. These findings underline the importance of the T cell response in influenza immunity and show that T cells are a potent target for future universal influenza vaccines.

[MECHANISMS OF ATTENUATION OF COLD-ADAPTED STRAIN A/KRASNO- DAR/101/35/59 (H2N2)].

AIM: Study of mechanisms of attenuation of cold-adapted (ca) influenza virus strain A/ Krasnodar/101/35/59 (H2N2), associated with disruption of NS1 protein functions. MATERIALS AND METHODS: Study of interferonogenic activity of ca strain A/Krasnodar/101/35/59 (H2N2), its parent variant A/Krasnodar/101/59 (H2N2), virulent strain A/WSN/33 (H1N1) and a number of single gene and multiple gene reassortants between these strains, obtained using reverse genetics, was carried out. Study of dynamics of IFNß gene expression was carried out by using a methodical approach of RT-PCR in real time mode. RESULTS: Inclusion of PB-1 gene of ca strain A/ Krasnodar/101/35/59 (H2N2) with reversion to wild type into genome composition of virulent strain A/WSN/33 (H1N1) does not result in a sharp change of interferonogenic activity of the reassortant. At the same time, similar inclusion of PB-1 gene of ca strain resulted in an incredible growth of interferonogenic activity of the reassortant. On the other hand, inclusion of NP-gene of wild type strain A/Krasnodar/101/59 (H2N2) into genome composition of the wild type strain A/WSN/33 did not differ by effect on interferonogenicity of the reassortant from inclusion of NP-gene of ca strain. CONCLUSION: Both constellations of genes of parent variants and mutations localized in these genes could affect formation of attenuation phenotype of reassortants. The data obtained allow to assume possible mechanisms of attenuation of ca strains, associated with disruption.of NS gene function.

Replication of live attenuated cold-adapted H2N2 influenza virus vaccine candidates in non human primates.

The development of an H2N2 vaccine is a priority in pandemic preparedness planning. We previously showed that a single dose of a cold-adapted (ca) H2N2 live attenuated influenza vaccine (LAIV) based on the influenza A/Ann Arbor/6/60 (AA ca) virus was immunogenic and efficacious in mice and ferrets. However, in a Phase I clinical trial, viral replication was restricted and immunogenicity was poor. In this study, we compared the replication of four H2N2 LAIV candidate viruses, AA ca, A/Tecumseh/3/67 (TEC67 ca), and two variants of A/Japan/305/57 (JAP57 ca) in three non-human primate (NHP) species: African green monkeys (AGM), cynomolgus macaques (CM) and rhesus macaques (RM). One JAP57 ca virus had glutamine and glycine at HA amino acid positions 226 and 228 (Q-G) that binds to α2-3 linked sialic acids, and one had leucine and serine that binds to α2-3 and α2-6 linked residues (L-S). The replication of all ca viruses was restricted, with low titers detected in the upper respiratory tract of all NHP species, however replication was detected in significantly more CMs than AGMs. The JAP57 ca Q-G and TEC67 ca viruses replicated in a significantly higher percentage of NHPs than the AA ca virus, with the TEC67 ca virus recovered from the greatest percentage of animals. Altering the receptor specificity of the JAP57 ca virus from α2-3 to both α2-3 and α2-6 linked sialic acid residues did not significantly increase the number of animals infected or the titer to which the virus replicated. Taken together, our data show that in NHPs the AA ca virus more closely reflects the human experience than mice or ferret studies. We suggest that CMs and RMs may be the preferred species for evaluating H2N2 LAIV viruses, and the TEC67 ca virus may be the most promising H2N2 LAIV candidate for further evaluation.

Risk assessment of H2N2 influenza viruses from the avian reservoir.

H2N2 influenza A viruses were the cause of the 1957-1958 pandemic. Historical evidence demonstrates they arose from avian virus ancestors, and while the H2N2 subtype has disappeared from humans, it persists in wild and domestic birds. Reemergence of H2N2 in humans is a significant threat due to the absence of humoral immunity in individuals under the age of 50. Thus, examination of these viruses, particularly those from the avian reservoir, must be addressed through surveillance, characterization, and antiviral testing. The data presented here are a risk assessment of 22 avian H2N2 viruses isolated from wild and domestic birds over 6 decades. Our data show that they have a low rate of genetic and antigenic evolution and remained similar to isolates circulating near the time of the pandemic. Most isolates replicated in mice and human bronchial epithelial cells, but replication in swine tissues was low or absent. Multiple isolates replicated in ferrets, and 3 viruses were transmitted to direct-contact cage mates. Markers of mammalian adaptation in hemagglutinin (HA) and PB2 proteins were absent from all isolates, and they retained a preference for avian-like α2,3-linked sialic acid receptors. Most isolates remained antigenically similar to pandemic A/Singapore/1/57 (H2N2) virus, suggesting they could be controlled by the pandemic vaccine candidate. All viruses were susceptible to neuraminidase inhibitors and adamantanes. Nonetheless, the sustained pathogenicity of avian H2N2 viruses in multiple mammalian models elevates their risk potential for human infections and stresses the need for continual surveillance as a component of prepandemic planning.

Evaluation of the pooling of swabs for real-time PCR detection of low titre shedding of low pathogenicity avian influenza in turkeys.

The purpose of this study was to determine whether pooling avian influenza (AI)-positive swabs with negative swabs has a detrimental effect on the sensitivity of AI real-time reverse transcription-polymerase chain reactions (rRT-PCRs). Cloacal and buccal swabs were sampled daily from 12 turkeys infected with A/goose/England/07(H2N2). For half the turkeys, each swab was mixed with four swabs from known AI-negative turkeys, and for the other half the swabs were tested individually. Bayesian modelling was used to (i) determine whether pooling the positive swabs compromised the cycle threshold (C(t)) value obtained from the rRT-PCRs, and (ii) estimate the likelihood of detection of an H2N2 infected turkey flock via rRT-PCR for pooled and individually tested swabs (cloacal and buccal) vs. the number of days post-infection of the flock. Results indicated that there was no significant effect of compromising AI rRT-PCR sensitivity by pooling a weak positive swab with negative swabs on the Ct values which were obtained. Pooled sampling was able to widen the detection window compared to individual sampling, for the same number of rRT-PCR tests. This indicates that pooled sampling would be an effective method of reducing the number of tests to be performed to determine flock status during an AI outbreak and for surveillance.

An open-label phase I trial of a live attenuated H2N2 influenza virus vaccine in healthy adults.

BACKGROUND: Live attenuated influenza vaccines (LAIV) against a variety of strains of pandemic potential are being developed and tested. We describe the results of an open-label phase I trial of a live attenuated H2N2 virus vaccine. OBJECTIVES: To evaluate the safety, infectivity, and immunogenicity of a live attenuated H2N2 influenza virus vaccine. PARTICIPANTS/METHODS: The A/Ann Arbor/6/60 (H2N2) virus used in this study is the attenuated, cold-adapted, temperature-sensitive strain that provides the genetic backbone of seasonal LAIV (MedImmune). We evaluated the safety, infectivity, and immunogenicity of two doses of 10(7) TCID(50) of this vaccine administered by nasal spray 4 weeks apart to normal healthy seronegative adults. RESULTS: Twenty-one participants received a first dose of the vaccine; 18 participants received a second dose. No serious adverse events occurred during the trial. The most common adverse events after vaccination were headache and musculoskeletal pain. The vaccine was restricted in replication: 24% and 17% had virus detectable by culture or rRT-PCR after the first and second dose, respectively. Antibody responses to the vaccine were also restricted: 24% of participants developed an antibody response as measured by either hemagglutination-inhibition assay (10%), or ELISA for H2 HA-specific serum IgG (24%) or IgA (16%) after either one or two doses. None of the participants had a neutralizing antibody response. Vaccine-specific IgG-secreting cells as measured by enzyme-linked immunospot increased from a mean of 0·5 to 2·0/10(6) peripheral blood mononuclear cells (PBMCs); vaccine-specific IgA-secreting cells increased from 0·1 to 0·5/10(6) PBMCs. CONCLUSIONS: The live attenuated H2N2 1960 AA ca vaccine demonstrated a safety profile consistent with seasonal trivalent LAIV but was restricted in replication and minimally immunogenic in healthy seronegative adults.

A 27-amino-acid deletion in the neuraminidase stalk supports replication of an avian H2N2 influenza A virus in the respiratory tract of chickens.

The events and mechanisms that lead to interspecies transmission of, and host adaptation to, influenza A virus are unknown; however, both surface and internal proteins have been implicated. Our previous report highlighted the role that Japanese quail play as an intermediate host, expanding the host range of a mallard H2N2 virus, A/mallard/Potsdam/178-4/83 (H2N2), through viral adaptation. This quail-adapted virus supported transmission in quail and increased its host range to replicate and be transmitted efficiently in chickens. Here we report that of the six amino acid changes in the quail-adapted virus, a single change in the hemagglutinin (HA) was crucial for transmission in quail, while the changes in the polymerase genes favored replication at lower temperatures than those for the wild-type mallard virus. Reverse genetic analysis indicated that all adaptive mutations were necessary for transmission in chickens, further implicating quail in extending this virus to terrestrial poultry. Adaptation of the quail-adapted virus in chickens resulted in the alteration of viral tropism from intestinal shedding to shedding and transmission via the respiratory tract. Sequence analysis indicated that this chicken-adapted virus maintained all quail-adaptive mutations, as well as an additional change in the HA and, most notably, a 27-amino-acid deletion in the stalk region of neuraminidase (NA), a genotypic marker of influenza virus adaptation to chickens. This stalk deletion was shown to be responsible for the change in virus tropism from the intestine to the respiratory tract.

Master donor viruses A/Leningrad/134/17/57 (H2N2) and B/USSR/60/69 and derived reassortants used in live attenuated influenza vaccine (LAIV) do not display neurovirulent properties in a mouse model.

Demonstration of the absence of neurovirulent properties of reassortant viruses contained in live attenuated influenza vaccine (LAIV) is a regulatory requirement. A mouse model was used to detect neurovirulent properties of the cold-adapted, temperature-sensitive and attenuated influenza master donor viruses (MDVs) A/Leningrad/134/17/57 (H2N2) and B/USSR/60/69 and derived reassortant influenza viruses. A/NWS/33 (H1N1), which is known to be neurovirulent in mice, was used as a positive control. Under conditions where the positive control virus induced symptoms of disease and showed viral replication in the upper respiratory tract as well as in the brain, replication of the influenza master donor viruses and reassortant influenza A and B viruses was limited to the upper respiratory tract where they were administered. None of the mice inoculated with MDVs or reassortant influenza viruses suffered from disease, and no virus or viral replication was observed in the brains of these mice. The results demonstrate the absence of neurovirulent properties of the MDVs and reassortant influenza viruses derived therefrom used in LAIV.

In vitro antiviral activity of favipiravir (T-705) against drug-resistant influenza and 2009 A(H1N1) viruses.

Favipiravir (T-705) has previously been shown to have a potent antiviral effect against influenza virus and some other RNA viruses in both cell culture and in animal models. Currently, favipiravir is undergoing clinical evaluation for the treatment of influenza A and B virus infections. In this study, favipiravir was evaluated in vitro for its ability to inhibit the replication of a representative panel of seasonal influenza viruses, the 2009 A(H1N1) strains, and animal viruses with pandemic (pdm) potential (swine triple reassortants, H2N2, H4N2, avian H7N2, and avian H5N1), including viruses which are resistant to the currently licensed anti-influenza drugs. All viruses were tested in a plaque reduction assay with MDCK cells, and a subset was also tested in both yield reduction and focus inhibition (FI) assays. For the majority of viruses tested, favipiravir significantly inhibited plaque formation at 3.2 muM (0.5 microg/ml) (50% effective concentrations [EC(50)s] of 0.19 to 22.48 muM and 0.03 to 3.53 microg/ml), and for all viruses, with the exception of a single dually resistant 2009 A(H1N1) virus, complete inhibition of plaque formation was seen at 3.2 muM (0.5 microg/ml). Due to the 2009 pandemic and increased drug resistance in circulating seasonal influenza viruses, there is an urgent need for new drugs which target influenza. This study demonstrates that favipiravir inhibits in vitro replication of a wide range of influenza viruses, including those resistant to currently available drugs.

Infection of human retinal pigment epithelial cells with influenza A viruses.

PURPOSE: Ocular involvement in influenza A virus diseases is common but usually limited to mild conjunctivitis. Rarely, inflammation of the choriocapillaris may result in atrophia of the retinal pigment epithelium (RPE). Primary human retinal pigment epithelial (RPE) cells were infected with seasonal (H1N1 A/New Caledonia/20/99, H3N2 A/California/7/2004) or highly pathogenic avian H5N1 (A/Thailand/1(Kan-1)/04, A/Vietnam/1203/04, A/Vietnam/1194/04) influenza strains. METHODS: Influenza A virus replication was studied by investigation of cytopathogenic effects, immune staining for influenza A virus nucleoprotein, determination of virus titers, and electron microscopy. Apoptosis induction was examined by immune staining for activated caspase 3 and cleaved PARP. Proinflammatory gene expression was investigated by quantitative PCR. RESULTS: H5N1 but not seasonal influenza strains replicated to high titers (>10(8) TCID(50)/mL; 50% tissue culture infectious dose/milliliter) in RPE cells. H5N1 infection resulted in RPE cell apoptosis that was abolished by the antiviral drug ribavirin. Pretreatment with type I interferons (interferon-alpha and -beta) or the type II interferon, (interferon-gamma), inhibited H5N1 replication. Moreover, H5N1 infection induced expression of proinflammatory genes (tumor necrosis factor-alpha, CXCL8, CXCL10, CXCL11, and interleukin-6), which was inhibited by ribavirin in a concentration-dependent manner. CONCLUSIONS: A novel cell type derived from the central nervous system was permissive to H5N1 influenza virus replication. This findings supports those suggesting H5N1 influenza strains to own a greater potential to spread to nonrespiratory tissues than seasonal human influenza viruses. Moreover, the data warrant the further study of the role of influenza A virus replication in retinal diseases associated with influenza A virus infections.

Chronic alcohol consumption increases the severity of murine influenza virus infections.

Respiratory infections with both seasonal as well as potential pandemic Influenza viruses represent a significant burden on human health. Furthermore, viruses such as Influenza are increasingly recognized as important etiologic agents in community acquired pneumonia. Within the U.S. alone, approximately 12.9 million people are heavy drinkers and chronic abuse of alcohol is known to increase the risk and severity of community acquired pneumonia. Given the lack of knowledge regarding Influenza disease in this population, we determined the effects of chronic alcohol consumption on Influenza virus infection. Herein, we report that mice exposed to chronic ethanol have sharp increases in morbidity, mortality, and pulmonary virus titers relative to controls. These increases in influenza severity correspond with inhibited pulmonary influenza-specific CD8 T cell responses. Further, chronic ethanol consumption results in an enhanced pulmonary lesion severity, similar to that recently described for pandemic influenzas. Together, our results suggest that chronic alcohol consumption may increase the risk for severe influenza virus infections by altering the pulmonary inflammatory environment and CD8 T cell response.

Influenza virus protecting RNA: an effective prophylactic and therapeutic antiviral.

Another influenza pandemic is inevitable, and new measures to combat this and seasonal influenza are urgently needed. Here we describe a new concept in antivirals based on a defined, naturally occurring defective influenza virus RNA that has the potential to protect against any influenza A virus in any animal host. This "protecting RNA" (244 RNA) is incorporated into virions which, although noninfectious, deliver the RNA to those cells of the respiratory tract that are naturally targeted by infectious influenza virus. A 120-ng intranasal dose of this 244 protecting virus completely protected mice against a simultaneous challenge of 10 50% lethal doses with influenza A/WSN (H1N1) virus. The 244 virus also protected mice against strong challenge doses of all other subtypes tested (i.e., H2N2, H3N2, and H3N8). This prophylactic activity was maintained in the animal for at least 1 week prior to challenge. The 244 virus was 10- to 100-fold more active than previously characterized defective influenza A viruses, and the protecting activity was confirmed to reside in the 244 RNA molecule by recovering a protecting virus entirely from cloned cDNA. There was a clear therapeutic benefit when the 244 virus was administered 24 to 48 h after a lethal challenge, an effect which has not been previously observed with any defective virus. Protecting virus reduced, but did not abolish, replication of challenge virus in mouse lungs during both prophylactic and therapeutic treatments. Protecting virus is a novel antiviral, having the potential to combat human influenza virus infections, particularly when the infecting strain is not known or is resistant to antiviral drugs.

Molecular mechanisms of reversion to the ts+ (non-temperature-sensitive) phenotype of influenza A cold-adapted (ca) virus strains.

A ts+ ca- (non-temperature-sensitive, non-cold-adapted) revertant of the A/Leningrad/134/47/57 ca strain influenza virus [A/Leningrad/134/47/ts+18/1957(H2N2)], obtained in our previous study, lost phenotypic manifestation of ts mutations by the PB2, NP and NS genes, although, according to sequencing data, it acquired only two true reversions of a mutation in the PB2 and PB1 genes. Direct sequencing showed the appearance of 27 additional mutations (13 coding) in the genes encoding the PB2, PB1, PA, NP, M and NS proteins of the revertant, along with the above-mentioned two true reversions. We conjecture that some of these mutations suppressed phenotypic manifestation of ts mutations in the NS and NP genes.

Adaptation of influenza A/Mallard/Potsdam/178-4/83 H2N2 virus in Japanese quail leads to infection and transmission in chickens.

To assess the potential of quail as an intermediate host of avian influenza, we tested the influenza A/Mallard/ Potsdam/178-4/83 (H2N2) virus to determine whether through adaptation a mallard strain can replicate and transmit in quail, as well as other terrestrial birds. After five serial passages of lung homogenate a virus arose that replicated and transmitted directly to contact cage mates. To test whether adaptation in quail led to interspecies transmission, white leghorn chickens were infected with the wild-type (mall/178) and quail-adapted (qa-mall/178) viruses. The results show that mall/178 H2N2 does not establish an infection in chickens nor does it transmit, while qa-mall/178 H2N2 infects and transmits to contact chickens causing clinical signs like depression and diarrhea. Completed sequences indicate six amino acid changes spanning four genes, PB2, PB1, HA, and NP, suggesting that the internal genes play a role in host adaptation. Further adaptation of qa-mall/178 in white leghorn chickens created a virus that replicated more efficiently in the upper and lower respiratory tract. Sequence analysis of the chicken-adapted virus points to a deletion in the neuraminidase stalk region.

[Molecular mechanisms of reversions to the ts+ -phenotype of cold-adapted influenza virus A strains--attenuation donors for live influenza reassortant vaccines].

A ts+ revertant of cold-adapted (ca) strain A/Leningrad/134/47/57--the attenuation donor for live influenza reassortant vaccines--was obtained by passages of the ca strain in chick embryos at nonpermissive temperatures. The ts+ revertant acquired the ability to grow in chick embryos at 40 degrees C and lost the capacity to reproduce there at 25 degrees C. A complementation-recombination test using the fowl plague virus (FPV0 ts-mutants showed the loss of the ts-phenotype in the RNA-segments of ts+ revertants' genome coding for PB2, NP, and NS (NS2) proteins. However, PCR-restriction analysis revealed a true reversion in RNA-segment coding for PB2 protein only. All the investigated mutations in the ts+ revertant genome were preserved. This phenomenon could be explained by the appearance of intragenic and extragenic suppression mutations in the ts+ revertant genome. The data of the complementation-recombination test suggest that reversion of ts-phenotype occurs more frequently due to extra- or intragenic suppression rather than as a result of a true mutation loss. Estimation of the genetic stability of vaccine ca strains of influenza virus should be based on the combined use of PCR-restriction and complementation tests.

In vivo antiviral activity: defective interfering virus protects better against virulent Influenza A virus than avirulent virus.

A defective interfering (DI) virus differs from the infectious virus from which it originated in having at least one major deletion in its genome. Such DI genomes are replicated only in cells infected in trans with homologous infectious virus and, as their name implies, they interfere with infectious virus replication and reduce the yield of progeny virus. This potent antiviral activity has been abundantly demonstrated in cell culture with many different DI animal viruses, but few in vivo examples have been reported, with the notable exception of DI Influenza A virus. A clue to this general lack of success arose recently when an anomaly was discovered in which DI Influenza A virus solidly protected mice from lethal disease caused by A/PR/8/34 (H1N1) and A/WSN/40 (H1N1) viruses, but protected only marginally from disease caused by A/Japan/305/57 (A/Jap, H2N2). The problem was not any incompatibility between the DI and infectious genomes, as A/Jap replicated the DI RNA in vivo. However, A/Jap required 300-fold more mouse infectious units to cause clinical disease than A/PR8 and it was hypothesized that it was this excess of infectivity that abrogated the protective activity of the DI virus. This conclusion was verified by varying the proportions of DI and challenge virus and showing that increasing the DI virus : infectious virus ratio in infected mice resulted in interference. Thus, counter-intuitively, DI virus is most effective against viruses that cause disease with low numbers of particles, i.e. virulent viruses.