Molecular evolution of H5N1 in Thailand between 2004 and 2008

Genetic evolution of hemagglutinin and neuraminidase genes of H5N1 highly pathogenic avian influenza viruses in Thailand

Background

Ongoing outbreaks of H5N1 highly pathogenic avian influenza (HPAI) viruses and the emergence of the genetic-related hemagglutinin (HA) gene of reassortant H5Nx viruses currently circulating in wild birds and poultries pose a great global public health concern. In this study, we comprehensively analyzed the genetic evolution of Thai H5N1 HA and neuraminidase (NA) genes between 2003 and 2010. The H5N1 Thailand virus clade 2.3.4 was also genetically compared to the currently circulating clade 2.3.4.4 of H5Nx viruses.

Methods

Full-length nucleotide sequences of 178 HA and 143 NA genes of H5N1 viruses circulating between 2003 and 2010 were phylogenetically analyzed using maximum likelihood (ML) phylogenetic construction. Bayesian phylogenetic trees were reconstructed using BEAST analysis with a Bayesian Markov chain Monte Carlo (MCMC) approach. The maximum clade credibility (MCC) tree was determined, and the time of the most recent common ancestor (tMRCA) was estimated. The H5N1 HA nucleotide sequences of clade 2.3.4 Thailand viruses were phylogenetically analyzed using ML phylogenetic tree construction and analyzed for nucleotide similarities with various subtypes of reassortant H5Nx HA clade 2.3.4.4.

Results

ML phylogenetic analysis revealed two distinct HA clades, clade 1 and clade 2.3.4, and two distinct NA groups within the corresponding H5 clade 1 viruses. Bayesian phylogenetic reconstruction for molecular clock suggested that the Thai H5N1 HA and NA emerged in 2001.87 (95% HPD: 2001.34-2002.49) and 2002.38 (95% HPD: 2001.99-2002.82), respectively, suggesting that the virus existed before it was first reported in 2004. The Thai H5N1 HA clade 2.3.4 was grouped into corresponding clades 2.3.4, 2.3.4.1, 2.3.4.2, and 2.3.4.3, and shared nucleotide similarities to reassortant H5Nx clade 2.3.4.4 ranged from 92.4-96.8%. Phylogenetic analysis revealed monophyletic H5Nx clade 2.3.4.4 evolved from H5N1 clade 2.3.4.

Conclusion

H5N1 viruses existed, and were presumably introduced and circulated in avian species in Thailand, before they were officially reported in 2004. HA and NA genes continuously evolved during circulation between 2004 and 2010. This study provides a better understanding of genetic evolution with respect to molecular epidemiology. Monitoring and surveillance of emerging variants/reassortants should be continued.

Avian influenza in the Greater Mekong Subregion, 2003-2018

The persistent circulation of avian influenza viruses (AIVs) is an ongoing problem for many countries in South East Asia, causing large economic losses to both the agricultural and health sectors. This review analyses AIV diversity, evolution and the risk of AIV emergence in humans in countries of the Greater Mekong Subregion (GMS): Cambodia, Laos, Myanmar, Thailand and Vietnam (excluding China). The analysis was based on AIV sequencing data, serological studies, published journal articles and AIV outbreak reports available from January 2003 to December 2018. All countries of the GMS have suffered losses due repeated outbreaks of highly pathogenic (HP) H5N1 that has also caused human cases in all GMS countries. In Laos, Myanmar and Vietnam AIV outbreaks in domestic poultry have also been caused by clade 2.3.4.4 H5N6. A diverse range of low pathogenic AIVs (H1-H12) have been detected in poultry and wild bird species, though surveillance for and characterization of these subtypes is limited. Subtype H3, H4, H6 and H11 viruses have been detected over prolonged periods; whilst H1, H2, H7, H8, H10 and H12 viruses have only been detected transiently. H9 AIVs circulate endemically in Cambodia and Vietnam with seroprevalence data indicating human exposure to H9 AIVs in Cambodia, Thailand and Vietnam. As surveillance studies focus heavily on the detection of H5 AIVs in domestic poultry further research is needed to understand the true level of AIV diversity and the risk AIVs pose to humans in the GMS.

Satellite telemetry tracks flyways of Asian Openbill storks in relation to H5N1 avian influenza spread and ecological change

BACKGROUND

Asian Openbills, Anastomus oscitans, have long been known to migrate from South to Southeast Asia for breeding and nesting. In Thailand, the first outbreak of H5N1 highly pathogenic avian influenza (HPAI) infection in the Openbills coincided with the outbreak in the poultry. Therefore, the flyways of Asian Openbills was determined to study their role in the spread of H5N1 HPAI virus to poultry and wild birds, and also within their flocks.

RESULTS

Flyways of 5 Openbills from 3 colonies were monitored using Argos satellite transmitters with positioning by Google Earth Programme between 2007 and 2013. None of the Openbills tagged with satellite telemeters moved outside of Thailand. Their home ranges or movement areas varied from 1.6 to 23,608 km2 per month (95% utility distribution). There was no positive result of the viral infection from oral and cloacal swabs of the Openbills and wild birds living in the vicinity by viral isolation and genome detection during 2007 to 2010 whereas the specific antibody was not detected on both Openbills and wild birds by using microneutralization assay after 2008. The movement of these Openbills did not correlate with H5N1 HPAI outbreaks in domestic poultry but correlated with rice crop rotation and populations of the apple snails which are their preferred food. Viral spread within the flocks of Openbills was not detected.

CONCLUSIONS

This study showed that Openbills played no role in the spread of H5N1 HPAI virus, which was probably due to the very low prevalence of the virus during the monitoring period. This study revealed the ecological factors that control the life cycle of Asian Openbills.

Genetic characterization of influenza A virus subtype H7N1 isolated from quail, Thailand

In Thailand, surveillance for the highly pathogenic avian influenza virus H5N1 (HPAI-H5N1) has revealed high prevalence of the virus in quail in live-bird markets. This study monitored avian influenza viruses (AIVs) in quail farms in an area at high risk for HPAI-H5N1 over a 12-month period from 2009 to 2010. One-step real-time RT-PCR (rRT-PCR) results showed that 1.18 % of swab samples (24/2,040) were AIV positive. Among the rRT-PCR positive samples, three samples were identified as subtype H7N1. One Thai H7N1 virus designated "A/quail/Thailand/CU-J2882/2009 (H7N1)" was subjected to whole genome sequencing and genetic characterization. Phylogenetic analysis showed that the HA gene of the Thai H7N1 virus groups with those of the H7 Eurasian viruses. Interestingly, the NA gene of the virus was found to be closely related to those of the HPAI-H5N1 viruses from Vietnam and Thailand. This study constitutes the first report on AIV H7N1 in Thailand. Our results suggest the possibility of genetic reassortment between AIV-H7NX and HPAI-H5N1 in quail. The HA cleavage site of the Thai H7N1 virus contains no multiple amino acid insertions, suggesting low pathogenic characteristics for this virus.

Evolutionary and Ecological Dynamics of Transboundary Disease Caused by H5N1 Virus in Southeast Asia

Southeast Asia has been the breeding ground for many emerging diseases in the past decade, and it is in this region that new genetic variants of HPAI H5N1 viruses have been emerging. Cross-border movement of animals accelerates the spread of H5N1, and the changing environmental conditions also exert strong selective pressure on the viruses. The transboundary zoonotic diseases caused by H5N1 pose a serious and continual threat to global economy and public health. Here, we divided the H5N1 viruses isolated in Southeast Asia during 2003-2009 into four groups according to their phylogenetic relationships among HA gene sequences. Molecular evolution analysis suggests populations in expansion rather than a positive selection for group 2 and group 3, yet group 4 is under strong positive selection. Site 193 was found to be a potential glycosylation site and located in receptor-binding domain. Note that site 193 tends to appear in avian isolates instead of human strains. Population dynamics analysis reveals that the effective population size of infections in Southeast Asia has undergone three obvious increases, and the results are consistent with the epidemiological analysis. Ecological and phylogeographical analyses show that agro-ecological environments, migratory birds, domestic waterfowl, especially free-ranging ducks, are crucial in the occurrence, maintenance and spread of H5N1 virus. The epidemiological links between Indonesia and Suphanburi observed suggest that viruses in Indonesia were originated from multiple introductions.

Satellite tracking on the flyways of brown-headed gulls and their potential role in the spread of highly pathogenic avian influenza H5N1 virus

Brown-headed gulls (Larus brunnicephalus), winter visitors of Thailand, were tracked by satellite telemetry during 2008-2011 for investigating their roles in the highly pathogenic avian influenza (HPAI) H5N1 virus spread. Eight gulls negative for influenza virus infection were marked with solar-powered satellite platform transmitters at Bang Poo study site in Samut Prakarn province, Thailand; their movements were monitored by the Argos satellite tracking system, and locations were mapped. Five gulls completed their migratory cycles, which spanned 7 countries (China, Bangladesh, India, Myanmar, Thailand, Cambodia, and Vietnam) affected by the HPAI H5N1 virus. Gulls migrated from their breeding grounds in China to stay overwinter in Thailand and Cambodia; while Bangladesh, India, Myanmar, and Vietnam were the places of stopovers during migration. Gulls traveled an average distance of about 2400 km between Thailand and China and spent 1-2 weeks on migration. Although AI surveillance among gulls was conducted at the study site, no AI virus was isolated and no H5N1 viral genome or specific antibody was detected in the 75 gulls tested, but 6.6% of blood samples were positive for pan-influenza A antibody. No AI outbreaks were reported in areas along flyways of gulls in Thailand during the study period. Distance and duration of migration, tolerability of the captive gulls to survive the HPAI H5N1 virus challenge and days at viral shedding after the virus challenging suggested that the Brown-headed gull could be a potential species for AI spread, especially among Southeast Asian countries, the epicenter of H5N1 AI outbreak.

Avian influenza A H5N1 virus: a continuous threat to humans

We report the first case of severe pneumonia due to co-infection with the emerging avian influenza A (H5N1) virus subclade 2.3.2.1 and Mycoplasma pneumoniae. The patient was a returning traveller who had visited a poultry market in South China. We then review the epidemiology, virology, interspecies barrier limiting poultry-to-human transmission, clinical manifestation, laboratory diagnosis, treatment and control measures of H5N1 clades that can be transmitted to humans. The recent controversy regarding the experiments involving aerosol transmission of recombinant H5N1 virus between ferrets is discussed. We also review the relative contribution of the poor response to antiviral treatment and the virus-induced hyperinflammatory damage to the pathogenesis and the high mortality of this infection. The factors related to the host, virus or medical intervention leading to the difference in disease mortality of different countries remain unknown. Because most developing countries have difficulty in instituting effective biosecurity measures, poultry vaccination becomes an important control measure. The rapid evolution of the virus would adversely affect the efficacy of poultry vaccination unless a correctly matched vaccine was chosen, manufactured and administered in a timely manner. Vigilant surveillance must continue to allow better preparedness for another poultry or human pandemic due to new viral mutants.

Evolution of highly pathogenic avian influenza H5N1 viruses in Egypt indicating progressive adaptation

Highly pathogenic avian influenza (HPAI) virus of the H5N1 subtype was first diagnosed in poultry in Egypt in 2006, and since then the disease became enzootic in poultry throughout the country, affecting the poultry industry and village poultry as well as infecting humans. Vaccination has been used as a part of the control strategy to help to control the disease. Epidemiological data with sequence analysis of H5N1 viruses is important to link the mechanism of virus evolution in Egypt. This study describes the evolutionary pattern of Egyptian H5N1 viruses based on molecular characterization for the isolates collected from commercial poultry farms and village poultry from 2006 to 2011. Genetic analysis of the hemagglutinin (HA) gene was done by sequencing of the full-length H5 gene. The epidemiological pattern of disease outbreaks in Egyptian poultry farms seems to be seasonal with no specific geographic distribution across the country. The molecular epidemiological data revealed that there are two major groups of viruses: the classic group of subclade 2.2.1 and a variant group of 2.2.1.1. The classic group is prevailing mainly in village poultry and had fewer mutations compared to the originally introduced virus in 2006. Since 2009, this group has started to be transmitted back to commercial sectors. The variant group emerged by late 2007, was prevalent mainly in vaccinated commercial poultry, mutated continuously at a higher rate until 2010, and started to decline in 2011. Genetic analysis of the neuraminidase (NA) gene and the other six internal genes indicates a grouping of the Egyptian viruses similar to that obtained using the HA gene, with no obvious reassortments. The results of this study indicate that HPAI-H5N1 viruses are progressively evolving and adapting in Egypt and continue to acquire new mutations every season.

Influenza A virus surveillance in live-bird markets: first report of influenza A virus subtype H4N6, H4N9, and H10N3 in Thailand

A one-year influenza A survey was conducted in 10 live bird markets (LBMs) in H5N1 high-risk areas in Thailand from January to December 2009. The result from the survey showed that the occurrence of influenza A virus (IAV) in LBMs was 0.36% (19/5304). Three influenza A subtypes recovered from LBMs were H4N6 (n = 2), H4N9 (n = 1), and H10N3 (n = 16) from Muscovy ducks housed in one LBM in Bangkok. These influenza subtypes had never been reported in Thailand, and therefore such genetic diversity raises concern about potential genetic reassortment of the viruses in avian species in a particular setting. Two influenza A subtypes (H4N6 and H4N9) were isolated from oropharyngeal and cloacal swabs of the same duck, suggesting coinfection with two influenza subtypes and possible genetic reassortment in the bird. In addition, H10N3 infection in ducks housed in the same LBM was observed. These findings further support that LBMs are a potential source of IAV transmission and genetic reassortment.

Cloned cDNA of A/swine/Iowa/15/1930 internal genes as a candidate backbone for reverse genetics vaccine against influenza A viruses

Reverse genetics viruses for influenza vaccine production usually utilize the internal genes of the egg-adapted A/Puerto Rico/8/34 (PR8) strain. This egg-adapted strain provides high production yield in embryonated eggs but does not necessarily give the best yield in mammalian cell culture. In order to generate a reverse genetics viral backbone that is well-adapted to high growth in mammalian cell culture, a swine influenza isolate A/swine/Iowa/15/30 (H1N1) (rg1930) that was shown to give high yield in Madin-Darby canine kidney (MDCK) cells was used as the internal gene donor for reverse genetics plasmids. In this report, the internal genes from rg1930 were used for construction of reverse genetics viruses carrying a cleavage site-modified hemagglutinin (HA) gene and neuraminidase (NA) gene from a highly pathogenic H5N1 virus. The resulting virus (rg1930H5N1) was low pathogenic in vivo. Inactivated rg1930H5N1 vaccine completely protected chickens from morbidity and mortality after challenge with highly pathogenic H5N1. Protective immunity was obtained when chickens were immunized with an inactivated vaccine consisting of at least 2(9) HA units of the rg1930H5N1 virus. In comparison to the PR8-based reverse genetics viruses carrying the same HA and NA genes from an H5N1 virus, rg1930 based viruses yielded higher viral titers in MDCK and Vero cells. In addition, the reverse genetics derived H3N2 and H5N2 viruses with the rg1930 backbone replicated in MDCK cells better than the cognate viruses with the rgPR8 backbone. It is concluded that this newly established reverse genetics backbone system could serve as a candidate for a master donor strain for development of inactivated influenza vaccines in cell-based systems.

Evidence for differing evolutionary dynamics of A/H5N1 viruses among countries applying or not applying avian influenza vaccination in poultry

Highly pathogenic avian influenza (HPAI) H5N1 (clade 2.2) was introduced into Egypt in early 2006. Despite the control measures taken, including mass vaccination of poultry, the virus rapidly spread among commercial and backyard flocks. Since the initial outbreaks, the virus in Egypt has evolved into a third order clade (clade 2.2.1) and diverged into antigenically and genetically distinct subclades. To better understand the dynamics of HPAI H5N1 evolution in countries that differ in vaccination policy, we undertook an in-depth analysis of those virus strains circulating in Egypt between 2006 and 2010, and compared countries where vaccination was adopted (Egypt and Indonesia) to those where it was not (Nigeria, Turkey and Thailand). This study incorporated 751 sequences (Egypt n=309, Indonesia n=149, Nigeria n=106, Turkey n=87, Thailand n=100) of the complete haemagglutinin (HA) open reading frame, the major antigenic determinant of influenza A virus. Our analysis revealed that two main Egyptian subclades (termed A and B) have co-circulated in domestic poultry since late 2007 and exhibit different profiles of positively selected codons and rates of nucleotide substitution. The mean evolutionary rate of subclade A H5N1 viruses was 4.07×10(-3) nucleotide substitutions per site, per year (HPD 95%, 3.23-4.91), whereas subclade B possessed a markedly higher substitution rate (8.87×10(-3); 95% HPD 7.0-10.72×10(-3)) and a stronger signature of positive selection. Although the direct association between H5N1 vaccination and virus evolution is difficult to establish, we found evidence for a difference in the evolutionary dynamics of H5N1 viruses among countries where vaccination was or was not adopted. In particular, both evolutionary rates and the number of positively selected sites were higher in virus populations circulating in countries applying avian influenza vaccination for H5N1, compared to viruses circulating in countries which had never used vaccination. We therefore urge a greater consideration of the potential consequences of inadequate vaccination on viral evolution.

Neuraminidase inhibitor sensitivity and receptor-binding specificity of Cambodian clade 1 highly pathogenic H5N1 influenza virus

The evolution of the highly pathogenic H5N1 influenza virus produces genetic variations that can lead to changes in antiviral susceptibility and in receptor-binding specificity. In countries where the highly pathogenic H5N1 virus is endemic or causes regular epidemics, the surveillance of these changes is important for assessing the pandemic risk. In Cambodia between 2004 and 2010, there have been 26 outbreaks of highly pathogenic H5N1 influenza virus in poultry and 10 reported human cases, 8 of which were fatal. We have observed naturally occurring mutations in hemagglutinin (HA) and neuraminidase (NA) of Cambodian H5N1 viruses that were predicted to alter sensitivity to neuraminidase inhibitors (NAIs) and/or receptor-binding specificity. We tested H5N1 viruses isolated from poultry and humans between 2004 and 2010 for sensitivity to the NAIs oseltamivir (Tamiflu) and zanamivir (Relenza). All viruses were sensitive to both inhibitors; however, we identified a virus with a mildly decreased sensitivity to zanamivir and have predicted that a V149A mutation is responsible. We also identified a virus with a hemagglutinin A134V mutation, present in a subpopulation amplified directly from a human sample. Using reverse genetics, we verified that this mutation is adaptative for human α2,6-linked sialidase receptors. The importance of an ongoing surveillance of H5N1 antigenic variance and genetic drift that may alter receptor binding and sensitivities of H5N1 viruses to NAIs cannot be underestimated while avian influenza remains a pandemic threat.

Genetic characterization of 2008 reassortant influenza A virus (H5N1), Thailand

In January and November 2008, outbreaks of avian influenza have been reported in 4 provinces of Thailand. Eight Influenza A H5N1 viruses were recovered from these 2008 AI outbreaks and comprehensively characterized and analyzed for nucleotide identity, genetic relatedness, virulence determinants, and possible sites of reassortment. The results show that the 2008 H5N1 viruses displayed genetic drift characteristics (less than 3% genetic differences), as commonly found in influenza A viruses. Based on phylogenetic analysis, clade 1 viruses in Thailand were divided into 3 distinct branches (subclades 1, 1.1 and 1.2). Six out of 8 H5N1 isolates have been identified as reassorted H5N1 viruses, while other isolates belong to an original H5N1 clade. These viruses have undergone inter-lineage reassortment between subclades 1.1 and 1.2 and thus represent new reassorted 2008 H5N1 viruses. The reassorted viruses have acquired gene segments from H5N1, subclade 1.1 (PA, HA, NP and M) and subclade 1.2 (PB2, PB1, NA and NS) in Thailand. Bootscan analysis of concatenated whole genome sequences of the 2008 H5N1 viruses supported the reassortment sites between subclade 1.1 and 1.2 viruses. Based on estimating of the time of the most recent common ancestors of the 2008 H5N1 viruses, the potential point of genetic reassortment of the viruses could be traced back to 2006. Genetic analysis of the 2008 H5N1 viruses has shown that most virulence determinants in all 8 genes of the viruses have remained unchanged. In summary, two predominant H5N1 lineages were circulating in 2008. The original CUK2-like lineage mainly circulated in central Thailand and the reassorted lineage (subclades 1.1 and 1.2) predominantly circulated in lower-north Thailand. To prevent new reassortment, emphasis should be put on prevention of H5N1 viruses circulating in high risk areas. In addition, surveillance and whole genome sequencing of H5N1 viruses should be routinely performed for monitoring the genetic drift of the virus and new reassorted strains, especially in light of potential reassortment between avian and mammalian H5N1 viruses.

Evolutionary dynamics of multiple sublineages of H5N1 influenza viruses in Nigeria from 2006 to 2008

Highly pathogenic A/H5N1 avian influenza (HPAI H5N1) viruses have seriously affected the Nigerian poultry industry since early 2006. Previous studies have identified multiple introductions of the virus into Nigeria and several reassortment events between cocirculating lineages. To determine the spatial, evolutionary, and population dynamics of the multiple H5N1 lineages cocirculating in Nigeria, we conducted a phylogenetic analysis of whole-genome sequences from 106 HPAI H5N1 viruses isolated between 2006 and 2008 and representing all 25 Nigerian states and the Federal Capital Territory (FCT) reporting outbreaks. We identified a major new subclade in Nigeria that is phylogenetically distinguishable from all previously identified sublineages, as well as two novel reassortment events. A detailed analysis of viral phylogeography identified two major source populations for the HPAI H5N1 virus in Nigeria, one in a major commercial poultry area (southwest region) and one in northern Nigeria, where contact between wild birds and backyard poultry is frequent. These findings suggested that migratory birds from Eastern Europe or Russia may serve an important role in the introduction of HPAI H5N1 viruses into Nigeria, although virus spread through the movement of poultry and poultry products cannot be excluded. Our study provides new insight into the genesis and evolution of H5N1 influenza viruses in Nigeria and has important implications for targeting surveillance efforts to rapidly identify the spread of the virus into and within Nigeria.