Persistence Of Influenza Research Articles

Reassortment and Persistence of Influenza A Viruses from Diverse Geographic Origins within Australian Wild Birds: Evidence from a Small, Isolated Population of Ruddy Turnstones.

Australian lineages of avian influenza A viruses (AIVs) are thought to be phylogenetically distinct from those circulating in Eurasia and the Americas, suggesting the circulation of endemic viruses seeded by occasional introductions from other regions. However, processes underlying the introduction, evolution and maintenance of AIVs in Australia remain poorly understood. Waders (order Charadriiformes, family Scolopacidae) may play a unique role in the ecology and evolution of AIVs, particularly in Australia, where ducks, geese, and swans (order Anseriformes, family Anatidae) rarely undertake intercontinental migrations. Across a 5-year surveillance period (2011 to 2015), ruddy turnstones (Arenaria interpres) that "overwinter" during the Austral summer in southeastern Australia showed generally low levels of AIV prevalence (0 to 2%). However, in March 2014, we detected AIVs in 32% (95% confidence interval [CI], 25 to 39%) of individuals in a small, low-density, island population 90 km from the Australian mainland. This epizootic comprised three distinct AIV genotypes, each of which represent a unique reassortment of Australian-, recently introduced Eurasian-, and recently introduced American-lineage gene segments. Strikingly, the Australian-lineage gene segments showed high similarity to those of H10N7 viruses isolated in 2010 and 2012 from poultry outbreaks 900 to 1,500 km to the north. Together with the diverse geographic origins of the American and Eurasian gene segments, these findings suggest extensive circulation and reassortment of AIVs within Australian wild birds over vast geographic distances. Our findings indicate that long-term surveillance in waders may yield unique insights into AIV gene flow, especially in geographic regions like Oceania, where Anatidae species do not display regular inter- or intracontinental migration.IMPORTANCE High prevalence of avian influenza viruses (AIVs) was detected in a small, low-density, isolated population of ruddy turnstones in Australia. Analysis of these viruses revealed relatively recent introductions of viral gene segments from both Eurasia and North America, as well as long-term persistence of introduced gene segments in Australian wild birds. These data demonstrate that the flow of viruses into Australia may be more common than initially thought and that, once introduced, these AIVs have the potential to be maintained within the continent. These findings add to a growing body of evidence suggesting that Australian wild birds are unlikely to be ecologically isolated from the highly pathogenic H5Nx viruses circulating among wild birds throughout the Northern Hemisphere.

Longitudinal field studies reveal early infection and persistence of influenza A virus in piglets despite the presence of maternally derived antibodies

A longitudinal study was performed in three Danish farrow to grower (30 kilos) herds over a 4-month period to investigate the dynamics and clinical impacts of influenza A virus (IAV) infections. In each herd, four batches consisting of four sows each with five ear-tagged piglets were included. Nasal swabs and/or blood were sampled from the sows and/or the piglets prior to farrowing and at weeks 1, 3, and 5 and at the end of the nursery period. Clinical examinations were performed at each sampling time. The sows and piglets were tested for IAV and IAV antibodies in nasal swabs and blood samples, respectively. The results revealed three enzootically infected herds, where the majority of the pigs were infected during the first 5 weeks after birth. Infected piglets of only 3 days of age were detected in the farrowing unit, where the sows were also shedding virus. In all herds, low to moderate numbers of infected pigs (ranging from 3.6 to 20.7%) were found to be virus positive in nasal swabs at two consecutive sampling times. Furthermore, clinical signs of respiratory disease were associated with IAV detection. The findings of this study documented that IAV can persist in herds and that piglets as young as 3 days can be infected despite the presence of maternally derived antibodies.

Persistence of influenza on surfaces

Close contact transmission (either direct or large droplet/droplet nuclei) is considered the main driver of influenza outbreaks but there is limited information regarding the role of fomites in transmission. To investigate the surface stability of influenza strains and thereby the role of fomites in transmission. The viability and quantitative reverse transcription-polymerase chain reaction (qt-RT-PCR) signal of five influenza strains (A/PR/8/34/H1N1, A/Cal/7/09/H1N1, A/Cal/4/09/H1N1, A/Sol/54/06/H1N1, and A/Bris/59/07/H1N1) seeded on to three surfaces (cotton, microfibre, and stainless steel) were assessed over time. Coupons of material were seeded with 10μL of a 106-108pfu/mL suspension of cell culture-derived virus stock supplemented with 0.3% bovine serum albumin. Coupons were assayed by plaque assay and qt-RT-PCR at 1, 24h, and weekly for seven weeks using a vortex-mixing elution method. Viable virus was detected from coupons for up to two weeks (stainless steel) and one week (cotton and microfibre), whereas detection of viruses by PCR was made for the entire seven-week study period. No strain differences were found. Ninety-nine percent reduction values (as a function of the seeding stock) were determined to be 17.7h for cotton (R2=0.86), 34.3h for microfibre (R2=0.80), and 174.9h for stainless steel (R2=0.98). Viable influenza was recovered from surfaces for up to two weeks. By contrast, influenza could be detected by PCR for more than seven weeks. These results have important implications for determining infection control protocols, cleaning regimes and sampling methods in healthcare settings.

Studies of Influenza A/H1N1 A/Tomsk/13/2010 Virus Topology during Development of Infectious Process in Mammals.

Influenza A/H1N1 A/Tomsk/13/2010 virus registered in Siberia in 2010 proved to be an extremely pathogenic strain. Dynamic study of the topology of this influenza virus strain in the lungs, liver, kidneys, lymph nodes, and great vessels of infected mice was carried out. Influenza A virus was detected by immunohistochemical methods in cells of different histogenesis in all the studied organs throughout the observation period (days 1-30 postinfection), which indicated effective replication and long persistence of influenza A/H1N1 A/Tomsk/13/2010 virus in mammalian cells.

Characterization of Viral Load, Viability and Persistence of Influenza A Virus in Air and on Surfaces of Swine Production Facilities.

Indirect transmission of influenza A virus (IAV) in swine is poorly understood and information is lacking on levels of environmental exposure encountered by swine and people during outbreaks of IAV in swine barns. We characterized viral load, viability and persistence of IAV in air and on surfaces during outbreaks in swine barns. IAV was detected in pigs, air and surfaces from five confirmed outbreaks with 48% (47/98) of oral fluid, 38% (32/84) of pen railing and 43% (35/82) of indoor air samples testing positive by IAV RT-PCR. IAV was isolated from air and oral fluids yielding a mixture of subtypes (H1N1, H1N2 and H3N2). Detection of IAV RNA from air was sustained during the outbreaks with maximum levels estimated between 7 and 11 days from reported onset. Our results indicate that during outbreaks of IAV in swine, aerosols and surfaces in barns contain significant levels of IAV potentially representing an exposure hazard to both swine and people.

Spread and persistence of influenza A viruses in waterfowl hosts in the North American Mississippi migratory flyway.

While geographic distance often restricts the spread of pathogens via hosts, this barrier may be compromised when host species are mobile. Migratory waterfowl in the order Anseriformes are important reservoir hosts for diverse populations of avian-origin influenza A viruses (AIVs) and are assumed to spread AIVs during their annual continental-scale migrations. However, support for this hypothesis is limited, and it is rarely tested using data from comprehensive surveillance efforts incorporating both the temporal and spatial aspects of host migratory patterns. We conducted intensive AIV surveillance of waterfowl using the North American Mississippi Migratory Flyway (MMF) over three autumn migratory seasons. Viral isolates (n = 297) from multiple host species were sequenced and analyzed for patterns of gene dispersal between northern staging and southern wintering locations. Using a phylogenetic and nucleotide identity framework, we observed a larger amount of gene dispersal within this flyway rather than between the other three longitudinally identified North American flyways. Across seasons, we observed patterns of regional persistence of diversity for each genomic segment, along with limited survival of dispersed AIV gene lineages. Reassortment increased with both time and distance, resulting in transient AIV constellations. This study shows that within the MMF, AIV gene flow favors spread along the migratory corridor within a season, and also that intensive surveillance during bird migration is important for identifying virus dispersal on time scales relevant to pandemic responsiveness. In addition, this study indicates that comprehensive monitoring programs to capture AIV diversity are critical for providing insight into AIV evolution and ecology in a major natural reservoir. Migratory birds are a reservoir for antigenic and genetic diversity of influenza A viruses (AIVs) and are implicated in the spread of virus diversity that has contributed to previous pandemic events. Evidence for dispersal of avian-origin AIVs by migratory birds is rarely examined on temporal scales relevant to pandemic or panzootic threats. Therefore, characterizing AIV movement by hosts within a migratory season is important for implementing effective surveillance strategies. We conducted surveillance following birds along a major North American migratory route and observed that within a migratory season, AIVs rapidly reassorted and gene lineages were dispersed primarily within the migratory corridor. Patterns of regional persistence were observed across seasons for each gene segment. We show that dispersal of AIV gene lineages by migratory birds occurs quickly along migratory routes and that surveillance for AIVs threatening human and animal health should focus attention on these routes.

Prevalence of multiple subtypes of influenza A virus in Japanese wild raccoons

Raccoons (Procyon lotor), which are not native to Japan, have been suspected to transmit various pathogens by frequent intrusion into agricultural and residential areas. To determine influenza A virus seropositivity in raccoons in Japan, we examined a total of 634 raccoons captured in 19 towns (A–S) from 2009 to 2012. Agar gel precipitation tests showed that the antibody prevalence was 1.89% (12/634). All positive raccoons were captured in three towns (A–C) located within a radius of approximately 30km, and 75% had antibodies to multiple subtypes (H1, H3–5, N1, N6, and N8). H3 and N8 antibodies were most frequently detected (75%). Among all the raccoons captured, 67% (8/12) were found in town A in 2009 and 2010, and all five raccoons captured in 2010 had H3 and N8 antibodies, suggesting that transmission of the subtype might occur. H5 and N1 antibodies were also detected in two raccoons captured in town A. Virus neutralization tests examining the highly pathogenic avian influenza virus (HPAIV) H5N1 subtype (four isolates of which have been detected in Japan to date) and the low PAIV (LPAIV) H5N3 subtype showed that raccoon sera highly cross-reacted with three H5N1 strains (clade 2.5: Ck/Yamaguchi/7/04; clade 2.3.2.1: Whooper swan/Hokkaido/1/08 and Whooper swan/Hamanaka/11), while they displayed a low cross-reactivity with the antisera to the clade 2.2 virus (Ck/Miyazaki/K11/07) and H5N3 LPAIV (Whistling swan/Shimane/499/83). Thus, the origin of the H5N1 virus was not clearly defined. The viral M gene was detected in four antibody-negative raccoons captured in three towns by real-time reverse transcription-polymerase chain reaction (rRT-PCR) with high Ct values, although no virus was isolated. This study is the first report showing that raccoons of Japan were infected with multiple subtypes of influenza A virus, including H5N1. It remains to be elucidated how raccoons play a role in persistence of influenza A virus in nature and if they could pose risks to animal and human health, for example, by playing a role as “mixing vessel” to generate novel strains of influenza A virus.

Prognostic impact of diastolic blood pressure on long-term outcome in patients with non-ST-segment elevation myocardial infarction

Raccoons (Procyon lotor), which are not native to Japan, have been suspected to transmit various pathogens by frequent intrusion into agricultural and residential areas. To determine influenza A virus seropositivity in raccoons in Japan, we examined a total of 634 raccoons captured in 19 towns (A–S) from 2009 to 2012. Agar gel precipitation tests showed that the antibody prevalence was 1.89% (12/634). All positive raccoons were captured in three towns (A–C) located within a radius of approximately 30 km, and 75% had antibodies to multiple subtypes (H1, H3–5, N1, N6, and N8). H3 and N8 antibodies were most frequently detected (75%). Among all the raccoons captured, 67% (8/12) were found in town A in 2009 and 2010, and all five raccoons captured in 2010 had H3 and N8 antibodies, suggesting that transmission of the subtype might occur. H5 and N1 antibodies were also detected in two raccoons captured in town A. Virus neutralization tests examining the highly pathogenic avian influenza virus (HPAIV) H5N1 subtype (four isolates of which have been detected in Japan to date) and the low PAIV (LPAIV) H5N3 subtype showed that raccoon sera highly cross-reacted with three H5N1 strains (clade 2.5: Ck/Yamaguchi/7/04; clade 2.3.2.1: Whooper swan/Hokkaido/1/08 and Whooper swan/Hamanaka/11), while they displayed a low cross-reactivity with the antisera to the clade 2.2 virus (Ck/Miyazaki/K11/07) and H5N3 LPAIV (Whistling swan/Shimane/499/83). Thus, the origin of the H5N1 virus was not clearly defined. The viral M gene was detected in four antibody-negative raccoons captured in three towns by real-time reverse transcription-polymerase chain reaction (rRT-PCR) with high Ct values, although no virus was isolated. This study is the first report showing that raccoons of Japan were infected with multiple subtypes of influenza A virus, including H5N1. It remains to be elucidated how raccoons play a role in persistence of influenza A virus in nature and if they could pose risks to animal and human health, for example, by playing a role as “mixing vessel” to generate novel strains of influenza A virus.

Metapopulation dynamics enable persistence of influenza A, including A/H5N1, in poultry.

Highly pathogenic influenza A/H5N1 has persistently but sporadically caused human illness and death since 1997. Yet it is still unclear how this pathogen is able to persist globally. While wild birds seem to be a genetic reservoir for influenza A, they do not seem to be the main source of human illness. Here, we highlight the role that domestic poultry may play in maintaining A/H5N1 globally, using theoretical models of spatial population structure in poultry populations. We find that a metapopulation of moderately sized poultry flocks can sustain the pathogen in a finite poultry population for over two years. Our results suggest that it is possible that moderately intensive backyard farms could sustain the pathogen indefinitely in real systems. This fits a pattern that has been observed from many empirical systems. Rather than just employing standard culling procedures to control the disease, our model suggests ways that poultry production systems may be modified.

Strain-related variation in the persistence of influenza A virus in three types of water: distilled water, filtered surface water, and intact surface water

BackgroundThe persistence of influenza A (IA) virus in aquatic habitats has been demonstrated to be a determinant for virus transmission dynamics in wild duck populations. In this study, we investigated virus strain-related variation in persistence in water for nine wild duck isolated IA viruses of three subtypes (H3N8, H4N6, and H8N4).ResultsWe experimentally estimated the loss of infectivity over time in three different types of water: distilled, filtered surface water, and intact surface water. All viruses persisted longest in distilled water followed by filtered surface water with markedly reduced durations of persistence observed in the intact surface water. Strain-related variations were observed in distilled and filtered surface water but limited variation was observed in the intact surface water.ConclusionsOur findings suggest that the role of surface water for long-term (between years) maintenance of AI viruses in the environment may be limited, and suggest that the physico-chemical characteristics of water, as well as microorganisms, may be of strong importance. Results also indicate that the extent of strain-related variation observed in distilled water may overestimate persistence abilities for IA viruses in the wild and supports the need to develop experiments that account for these effects to assess subtype, genotype, as well as spatial and temporal variation in the persistence of IA viruses in aquatic habitats.

Temporally structured metapopulation dynamics and persistence of influenza A H3N2 virus in humans

Populations of seasonal influenza virus experience strong annual bottlenecks that pose a considerable extinction risk. It has been suggested that an influenza source population located in tropical Southeast or East Asia seeds annual temperate epidemics. Here we investigate the seasonal dynamics and migration patterns of influenza A H3N2 virus by analysis of virus samples obtained from 2003 to 2006 from Australia, Europe, Japan, New York, New Zealand, Southeast Asia, and newly sequenced viruses from Hong Kong. In contrast to annual temperate epidemics, relatively low levels of relative genetic diversity and no seasonal fluctuations characterized virus populations in tropical Southeast Asia and Hong Kong. Bayesian phylogeographic analysis using discrete temporal and spatial characters reveal high rates of viral migration between urban centers tested. Although the virus population that migrated between Southeast Asia and Hong Kong persisted through time, this was dependent on virus input from temperate regions and these tropical regions did not maintain a source for annual H3N2 influenza epidemics. We further show that multiple lineages may seed annual influenza epidemics, and that each region may function as a potential source population. We therefore propose that the global persistence of H3N2 influenza A virus is the result of a migrating metapopulation in which multiple different localities may seed seasonal epidemics in temperate regions in a given year. Such complex global migration dynamics may confound control efforts and contribute to the emergence and spread of antigenic variants and drug-resistant viruses.

Evolution and persistence of influenza A and other diseases

The evolution of the etiological agents of disease presents one of the greatest challenges for their control, and makes essential complementing standard epidemiological investigations with broader approaches that allow for evolutionary change. Given the stunning genetic diversity that is possible for many such agents, such as the influenza virus, it is impossible to represent all of the diversity manifest at the level of amino acid sequences. We show that drift-variant influenza strains naturally cluster into groups which are associated with functionally important epitopic regions. Dominant clusters typically replace each other every 2–5 years, and this feature is fundamental to the development of vaccination strategies. We furthermore show that stochastic fluctuations can greatly magnify small interference effects among strains, or even among subtypes, leading for example to competitive exclusion in situations where such effects would be unexpected based on the usual deterministic models. We suggest that this effect might be involved in the explanations of some persistent empirical anomalies.

Dynamics of annual influenza A epidemics with immuno-selection.

The persistence of Influenza A in the human population relies on continual changes in the viral surface antigens allowing the virus to reinfect the same hosts every few years. The epidemiology of such a drifting virus is modeled by a discrete season-to-season map. During the epidemic season only one strain is present and its transmission dynamics follows a standard epidemic model. After the season, cross-immunity to next year's virus is determined from the proportion of hosts that were infected during the season. A partial analysis of this map shows the existence of oscillations where epidemics occur at regular or irregular intervals.

Characterization of HeLa Cells Persistently Infected with Influenza Virus B/Lee/40 with Respect to Telomerase Activity and Apoptosis

Objective: The purpose of this study was to examine telomerase activity and apoptotic changes in HeLa cells persistently infected with influenza viruses B/Lee/40 (He/Le cells). Methods: He/Le cells were established as described previously [Intervirology 2002;45:67–70], and passaged twice a week. The existence of influenza virus genes was monitored by the reverse transcription polymerase chain reaction (RT-PCR). Telomerase activities in He/Le cells were assayed by Telochaser (stretch PCR method). Apoptotic changes in He/Le cells were examined using the Apoptotic DNA Ladder Kit and the In situ Cell Death Detection Kit, Fluorescence. Results: In He/Le cells, (1) all eight influenza virus genes were detected by RT-PCR until 62 days post infection (p.i.); (2) only nucleoprotein gene remained detectable until 120 days p.i.; (3) telomerase activity of He/Le cells normalized to those of uninfected HeLa cells was remarkably decreased (16–55% of control) during the persistence of influenza and recovered up to 80% of control on day 168 p.i. when no influenza virus gene was detected by RT-PCR, and (4) no apoptotic changes were detected despite the continuous existence of influenza virus genes. Conclusion: In He/Le cells, telomerase activity was suppressed exclusively during the persistence of influenza, and no apoptotic changes were detected.

Productive and non-productive phases during long-term persistence of influenza C virus

Persistent infection with a variant of influenza C/Ann Arbor/1/50 virus in MDCK cells has been previously reported. However, the precise molecular mechanism of persistence is still unknown. We show that the release of active progeny virus, as tested for by haemagglutination and acetylesterase profiles, does not take place in freshly seeded MDCK cells. Productive virus replication occurs simultaneously with massive production of structural proteins as shown by immunoprecipitation and immunofluorescence. PCR for the HEF structural protein-encoding segment 4 revealed that positive-sense RNA is present only during virus multiplication whereas negative-sense RNA appears to be constantly detectable. In this study we give initial evidence that influenza C virus can persist in the form of its genomic minus strand RNA, and plus strand transcription, protein synthesis and virus replication remain restricted to productive phases.

Persistence of Influenza A by Continuous Close-Contact Transmission: The Effect of Non-Random Mixing

The interaction of two populations has variable effects on the nature and duration of epidemic activity, depending on the transmissibility of the virus, the susceptibility of the population, migration, birth and death rates, and the initial number of cases. Under circumstances where transmission stops in a single population (the infectious contact number is less than or equal to one), transmission may continue indefinitely when two populations interact under many different parameter combinations. A mass-action model was constructed using difference equations for two populations that included parameters for migration between populations and variable transmissibility between and within these populations. The limitations of extrapolating the model to actual conditions in human populations result from assumptions inherent in these models, such as fractional infection of individuals.