Avian Influenza Virus Outbreaks Research Articles

Prevalence of avian influenza virus in wild birds before and after the HPAI H5N8 outbreak in 2014 in South Korea.

Since 2003, highly pathogenic avian influenza (HPAI) virus outbreaks have occurred five times in Korea, with four HPAI H5N1 outbreaks and one HPAI H5N8 outbreak. Migratory birds have been suggested to be the first source of HPAI in Korea. Here, we surveyed migratory wild birds for the presence of AI and compared regional AI prevalence in wild birds from September 2012 to April 2014 for birds having migratory pathways in South Korea. Finally, we investigated the prevalence of AI in migratory birds before and after HPAI H5N8 outbreaks. Overall, we captured 1617 migratory wild birds, while 18,817 feces samples and 74 dead birds were collected from major wild bird habitats. A total of 21 HPAI viruses were isolated from dead birds, and 86 low pathogenic AI (LPAI) viruses were isolated from captured birds and from feces samples. Spatiotemporal distribution analysis revealed that AI viruses were spread southward until December, but tended to shift north after January, consistent with the movement of migratory birds in South Korea. Furthermore, we found that LPAI virus prevalences within wild birds were notably higher in 2013-2014 than the previous prevalence during the northward migration season. The data from our study demonstrate the importance of the surveillance of AI in wild birds. Future studies including in-depth genetic analysis in combination with evaluation of the movement and ecology of migratory birds might help us to bridge the gaps in our knowledge and better explain, predict, and ultimately prevent future HPAI outbreaks.

Seroprevalence and Detection of Avian Influenza Type A in Ducks at Nikli and Bajitpur Upazila of Bangladesh

Waterfowl are the natural reservoir of avian influenza viruses and ducks may play a role in the maintenance of avian influenza type A. The aim of the present study was to investigate the seroprevalence and detection of avian influenza virus (AIV) type A in duck. This study was carried out during July 2013 to December 2013 on AIV type A from semi-scavenging farm at Nikli and Bajitpur upazila of Kishoregonj district in Bangladesh. A total of 368 blood samples were collected from duck and tested by indirect ELISA for seroprevalence. For detection of AIV type A, The cloacal swabs were collected from 75 duck and subjected to RNA extraction and real time RT-PCR (rRT-PCR) with specific primer and probe for detection of matrix (M) gene. The average seroprevalance of AIV type A in seven different age groups was found to be 90.21%. The highest (25.81 %) seroprevalence was found in 5 months age of birds and the lowest (2.44 %) was found in 12 months age of birds. As regard to area distribution, the average degree of seroprevalence was 93.51% from Nikli had the highest order than Bajitpur (86.88%) upazila of Bangladesh. In case of cloacal sample by using rRT–PCR, out of 15 pooling cloacal samples, two pooling samples (13.33%) that contain 10 samples were positive and 13 pooling samples showed negative (86.67%) for AIV type A in duck. It can be concluded that the long distance movement of duck flocks, may influence outbreak of avian influenza virus (AIV) type A among different poultry species in Bangladesh. Therefore, it needs to develop control strategy for future dissemination of AIV in duck population.DOI: http://dx.doi.org/10.3329/bjvm.v13i1.23705Bangl. J. Vet. Med. (2015). 13 (1): 5-9

Epidemiology, Evolution, and Recent Outbreaks of Avian Influenza Virus in China.

Novel reassortants of H7N9, H10N8, and H5N6 avian influenza viruses (AIVs) are currently circulating in China's poultry flocks, occasionally infecting humans and other mammals. Combined with the sometimes enzootic H5N1 and H9N2 strains, this cauldron of genetically diverse AIVs pose significant risks to public health. Here, we review the epidemiology, evolution, and recent outbreaks of AIVs in China, discuss reasons behind the recent increase in the emergence of novel AIVs, and identify warning signs which may point to the emergence of a potentially virulent and highly transmissible AIV to humans. This review will be useful to authorities who consider options for the detection and control of AIV transmission in animals and humans, with the goal of preventing future epidemics and pandemics.

Amino acid substitutions in the neuraminidase protein of an H9N2 avian influenza virus affect its airborne transmission in chickens.

Cases of H9N2 avian influenza virus (AIV) in poultry are increasing throughout many Eurasian countries, and co-infections with other pathogens have resulted in high morbidity and mortality in poultry. Few studies have investigated the genetic factors of virus airborne transmission which determine the scope of this epidemic. In this study, we used specific-pathogen-free chickens housed in isolators to investigate the airborne transmissibility of five recombinant H9N2 AIV rescued by reverse genetic technology. The results show that airborne transmission of A/Chicken/Shandong/01/2008 (SD01) virus was related to the neuraminidase (NA) gene, and four amino acid mutations (D368E, S370L, E313K and G381D) within the head region of the SD01 NA, reduced virus replication in the respiratory tract of chickens, reduced virus NA activity, and resulted in a loss of airborne transmission ability in chickens. Similarly, reverse mutations of these four amino acids in the NA protein of r01/NASS virus, conferred an airborne transmission ability to the recombinant virus. We conclude that these four NA residues may be significant genetic markers for evaluating potential disease outbreak of H9N2 AIV, and propose that immediate attention should be paid to the airborne transmission of this virus.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-014-0142-3) contains supplementary material, which is available to authorized users.

Phylogenetic Analysis of Hemagglutinin Genes of H9N2 Avian Influenza Viruses Isolated from Chickens in Shandong, China, between 1998 and 2013.

Since H9N2 avian influenza virus (AIV) was first isolated in Guangdong province of China, the virus has been circulating in chicken flocks in mainland China. However, a systematic phylogenetic analysis of H9N2 AIV from chickens in Shandong of China has not been conducted. Based on hemagglutinin (HA) gene sequences of H9N2 AIVs isolated from chickens in Shandong of China between 1998 and 2013, genetic evolution of 35 HA gene sequences was systematically analyzed in this study. Our findings showed that the majority of H9N2 AIVs (21 out of 35) belonged to the lineage h9.4.2.5. Most of isolates (33 out of 35) had a PSRSSR↓GLF motif in HA cleavage site. Importantly, 29 out of these 35 isolates had an amino acid exchange (Q226L) in the receptor-binding site. The substitution showed that H9N2 AIVs had the potential affinity to bind to human-like receptor. The currently prevalent H9N2 AIVs in Shandong belonged to the lineage h9.4.2.5 which are different from the vaccine strain SS/94 clade h9.4.2.3. Therefore, the long-term surveillance of H9N2 AIVs is of significance to combat the possible H9N2 AIV outbreaks.

Evaluation of avian influenza virus isolated from ducks as a potential live vaccine candidate against novel H7N9 viruses

Recent outbreaks of a novel H7N9 avian influenza virus in humans in China raise pandemic concerns and underscore an urgent need to develop effective vaccines. Theoretically, live influenza vaccines are of multiple advantages over traditional inactivated influenza vaccines to be used in a pandemic, because they can be produced rapidly, safely, and inexpensively. However, studies on live vaccines against the novel H7N9 virus are limited. In this study, we evaluated a potential live influenza vaccine candidate using an H7N3 avian influenza virus isolated from ducks with controls of two recombinant viruses generated through reverse genetics. The potential candidate could be produced efficiently using chicken embryonated eggs, and is homogenous to the novel H7N9 virus in their viral hemagglutinin genes. The potential candidate is likely low pathogenic to birds and mammals, and likely sensitive to oseltamivir and amantadine, as suggested by its genomic sequences. Its low pathogenicity was further supported through inoculation in mice, chicken embryonated eggs and chickens. Specific antibodies elicited in mice were detectable at least during the period between day 14 and day 56 after intranasal administration of the candidate for one time. Titers of the specific antibodies increased significantly with a boost intranasal administration or a higher inoculation dose. The induced specific antibodies were of substantial cross-reactivity with the novel H7N9 virus. These primary but promising evaluation data suggest that the duck influenza virus could be used as a potential live vaccine candidate, favorably through a prime-boost route, to mitigate the severity of the possible pandemic caused by the newly emerging H7N9 virus, and is valuable to be further evaluated.

Avian influenza H9N2 subtype in Poland – characterization of the isolates and evidence of concomitant infections

In April/May 2013, four outbreaks of avian influenza virus (AIV) infections caused by H9N2 subtype were diagnosed in Poland in fattening turkey flocks exhibiting a drop in feed and water intake, depression, respiratory signs and mortality. The subsequent serological survey carried out on samples collected between June 2012 and September 2013 from 92 poultry flocks detected positive sera in two additional meat turkey flocks located in the same province. The analysis of amino acids in the haemagglutinin and neuraminidase glycoproteins revealed that the detected H9N2 viruses possessed molecular profiles suggestive of low pathogenicity, avian-like SAα2,3 receptor specificity and adaptation to domestic poultry. Phylogenetic studies showed that these H9N2 AIVs grouped within the Eurasian clade of wild bird-origin AIVs and had no relationship with H9N2 AIV circulating in poultry in the Middle East and Far East Asia over the past decade. Experimentally infected SPF chickens with the index-case H9N2 virus remained healthy throughout the experiment. On the other hand, ten 3-week-old commercial turkeys infected via the oculonasal route showed respiratory signs and mortality (2/10 birds). Additional diagnostic tests demonstrated the consistent presence of DNA/RNA of Ornithobacterium rhinotracheale, Bordetella avium and, less frequently, of astro-, rota-, reo-, parvo- and adenoviruses in turkeys both from field outbreaks and laboratory experiment. Although no microbiological culture was performed, we speculate that these secondary pathogens could play a role in the pathogenicity of the current H9N2 infections.

Characterization and phylogenetic analysis of a highly pathogenic avian influenza H5N1 virus isolated from diseased ostriches (Struthio camelus) in the Kingdom of Saudi Arabia.

During 2007, two outbreaks of avian influenza virus (AIV) in backyard and commercial ostrich flocks were first reported in the Kingdom of Saudi Arabia (KSA). The infected ostriches suffered from depression, anorexia, and diarrhea and some exhibited sudden death. A rapid AIV-group antigen detection and real-time reverse-transcription PCR (rtRT-PCR) were initially performed on cloacal and tracheal swabs collected from diseased birds. Pools from positive-tested swabs for each flock were utilized for virus isolation in specific-pathogen-free embryonating chicken eggs. H5N1 AIV was identified in the harvested allantoic fluids by hemagglutination followed by hemagglutination inhibition and rtRT-PCR. The viruses responsible for these two outbreaks were sequenced and characterized as HPAIV H5N1 (A/ostrich/Saudi Arabia/6732-3/2007 and A/ostrich/Saudi Arabia/3489-73VIR08/ 2007) from backyard and commercial flocks, respectively. Phylogenetic analysis of both isolates revealed that the two viruses belong to clade 2.2 sublineage II and cluster with the HPAIV H5N1 isolated from falcons and turkeys during 2007 in KSA.

Evidence for H5 avian influenza infection in Zhejiang province, China, 2010-2012: a cross-sectional study.

The first outbreak of H5N1 highly-pathogenic avian influenza (HPAI) virus associated with several human deaths occurred in 1997 in Hong-Kong, China. While H5N1 virus infection in poultry workers has been studied in some detail, little is known about the environmental risk factors of the H5 avian influenza virus infection in China. A cross-sectional study was performed to evaluate the environmental load of H5 viruses in poultry-contaminated environments and to explore potential risk factors associated with infection in poultry workers between October 2010 and March 2012. Serum and environmental samples were collected in Zhejiang province, China. The hemagglutination inhibition (HI) assay was used to analyze human sera for antibodies against H5N1 virus [A/Hubei/1/2010 (H5N1) and A/Anhui/1/2005 (H5N1)]. All participants were interviewed with a standardized questionnaire to collect information on exposure to poultry. H5 Avian influenza virus in the environmental samples was detected by real time RT-PCR. One hundred and five of 3,453 environmental samples (3.0%) tested positive for H5 avian influenza virus. Fifty-five of 1,169 subjects (4.7%) tested seropositive for anti-H5N1 antibodies. A statistically significant difference in H5 virus detection rate was found among the different environments sampled (<0.001), with the highest showed in live bird markets (68.6%). Detection rate varied according to the source of samples, sewage (9.5%), drinking water (19.0%), feces (19.0%), cage surface (25.7%), and slaughtering chopping boards (15.2%), respectively. Direct or close contact with poultry (OR =5.20, 95% CI, 1.53-17.74) and breeding numerous poultry (OR =3.77, 95% CI, 1.72-8.73) were significantly associated with seroprevalence of antibodies to avian influenza virus A (H5N1). The number of birds bred more than 1,000 and direct or close contact with poultry in the workplace or the environment would be a potential risk of H5N1 infection.

Novel H7N9 influenza virus shows low infectious dose, high growth rate, and efficient contact transmission in the guinea pig model.

The zoonotic outbreak of H7N9 subtype avian influenza virus that occurred in eastern China in the spring of 2013 resulted in 135 confirmed human cases, 44 of which were lethal. Sequencing of the viral genome revealed a number of molecular signatures associated with virulence or transmission in mammals. We report here that, in the guinea pig model, a human isolate of novel H7N9 influenza virus, A/Anhui/1/2013 (An/13), is highly dissimilar to an H7N1 avian isolate and instead behaves similarly to a human seasonal strain in several respects. An/13 was found to have a low 50% infectious dose, grow to high titers in the upper respiratory tract, and transmit efficiently among cocaged guinea pigs. The pH of fusion of the hemagglutinin (HA) and the binding of virus to fixed guinea pig tissues were also examined. The An/13 HA displayed a relatively elevated pH of fusion characteristic of many avian strains, and An/13 resembled avian viruses in terms of attachment to tissues. One important difference was seen between An/13 and both the H3N2 human and the H7N1 avian viruses: when inoculated intranasally at a high dose, only the An/13 virus led to productive infection of the lower respiratory tract of guinea pigs. In sum, An/13 was found to retain fusion and attachment properties of an avian influenza virus but displayed robust growth and contact transmission in the guinea pig model atypical of avian strains and indicative of mammalian adaptation.

Epidemiological analysis of spatially misaligned data: a case of highly pathogenic avian influenza virus outbreak in Nigeria

This research is focused on the epidemiological analysis of the transmission of the highly pathogenic avian influenza (HPAI) H5N1 virus outbreak in Nigeria. The data included 145 outbreaks together with the locations of the infected farms and the date of confirmation of infection. In order to investigate the environmental conditions that favoured the transmission and spread of the virus, weather stations were realigned with the locations of the infected farms. The spatial Kolmogorov-Smirnov test for complete spatial randomness rejects the null hypothesis of constant intensity (P < 0·0001). Preliminary exploratory analysis showed an increase in the incidence of H5N1 virus at farms located at high altitude. Results from the Poisson log-linear conditional intensity function identified temperature (-0·9601) and wind speed (0·6239) as the ecological factors that influence the intensity of transmission of the H5N1 virus. The model also includes distance from the first outbreak (-0·9175) with an Akaike's Information Criterion of -103·87. Our analysis using a point process model showed that geographical heterogeneity, seasonal effects, temperature, wind as well as proximity to the first outbreak are very important components of spread and transmission of HPAI H5N1.

Geographical distribution of low pathogenic avian influenza viruses of domestic poultry in Vietnam and their genetic relevance with Asian isolates

From the avian influenza virus (AIV) outbreaks and market surveillances in Vietnam during November 2011 and March 2012, a total of 196 AIV were isolated. Although H5N1 highly pathogenic avian influenza (HPAI) was the most prevalent subtype in Vietnam, 57 low pathogenic avian influenza (LPAI) viruses were identified from mainly domestic ducks and some chickens. Of note, various subtypes of LPAI viruses were isolated from domestic ducks in Vietnam: H3 (n = 16), H4 (n = 4), H6 (n = 24), H7 (n = 1), and H9 (n = 10). Geographically, the LPAI viruses were identified in different regions of Vietnam. Phylogenetic analysis of HA and NA genes in LPAIV in Vietnam showed that some H3 (group I) and H4 subtypes AIV clustered with the viruses of several Asian isolates from domestic poultry and wild birds. However, the H6, H9, and some H3 (group II and III) subtypes AIV were closely related to isolates from domestic poultry in Southern China. In addition, whereas the N2 and N6 subtypes AIV belonged to the Eurasian lineage, the N8 subtype AIV was classified to be both of Eurasian and American lineage. These findings revealed that the regional trade and wild birds play a key role transmission of LPAIV in domestic ducks in Vietnam. Further surveillance at the intercountry level is needed to understand the epidemiology of these viruses and to cope with emergence of novel AIV types.

Broadly Protective Adenovirus-Based Multivalent Vaccines against Highly Pathogenic Avian Influenza Viruses for Pandemic Preparedness

Recurrent outbreaks of H5, H7 and H9 avian influenza viruses in domestic poultry accompanied by their occasional transmission to humans have highlighted the public health threat posed by these viruses. Newer vaccine approaches for pandemic preparedness against these viruses are needed, given the limitations of vaccines currently approved for H5N1 viruses in terms of their production timelines and the ability to induce protective immune responses in the absence of adjuvants. In this study, we evaluated the feasibility of an adenovirus (AdV)-based multivalent vaccine approach for pandemic preparedness against H5, H7 and H9 avian influenza viruses in a mouse model. Replication-defective AdV vectors expressing hemagglutinin (HA) from different subtypes and nucleoprotein (NP) from one subtype induced high levels of humoral and cellular immune responses and conferred protection against virus replication following challenge with H5, H7 and H9 avian influenza virus subtypes. Inclusion of HA from the 2009 H1N1 pandemic virus in the vaccine formulation further broadened the vaccine coverage. Significantly high levels of HA stalk-specific antibodies were observed following immunization with the multivalent vaccine. Inclusion of NP into the multivalent HA vaccine formulation resulted in the induction of CD8 T cell responses. These results suggest that a multivalent vaccine strategy may provide reasonable protection in the event of a pandemic caused by H5, H7, or H9 avian influenza virus before a strain-matched vaccine can be produced.

Quantifying transmission of highly pathogenic and low pathogenicity H7N1 avian influenza in turkeys.

Outbreaks of avian influenza in poultry can be devastating, yet many of the basic epidemiological parameters have not been accurately characterised. In 1999–2000 in Northern Italy, outbreaks of H7N1 low pathogenicity avian influenza virus (LPAI) were followed by the emergence of H7N1 highly pathogenic avian influenza virus (HPAI). This study investigates the transmission dynamics in turkeys of representative HPAI and LPAI H7N1 virus strains from this outbreak in an experimental setting, allowing direct comparison of the two strains. The fitted transmission rates for the two strains are similar: 2.04 (1.5–2.7) per day for HPAI, 2.01 (1.6–2.5) per day for LPAI. However, the mean infectious period is far shorter for HPAI (1.47 (1.3–1.7) days) than for LPAI (7.65 (7.0–8.3) days), due to the rapid death of infected turkeys. Hence the basic reproductive ratio, is significantly lower for HPAI (3.01 (2.2–4.0)) than for LPAI (15.3 (11.8–19.7)). The comparison of transmission rates and are critically important in relation to understanding how HPAI might emerge from LPAI. Two competing hypotheses for how transmission rates vary with population size are tested by fitting competing models to experiments with differing numbers of turkeys. A model with frequency-dependent transmission gives a significantly better fit to experimental data than density-dependent transmission. This has important implications for extrapolating experimental results from relatively small numbers of birds to the commercial poultry flock size, and for how control, including vaccination, might scale with flock size.

Avian Influenza (H5N1) Virus of Clade 2.3.2 in Domestic Poultry in India

South Asia has experienced regular outbreaks of H5N1 avian influenza virus since its first detection in India and Pakistan in February, 2006. Till 2009, the outbreaks in this region were due to clade 2.2 H5N1 virus. In 2010, Nepal reported the first outbreak of clade 2.3.2 virus in South Asia. In February 2011, two outbreaks of H5N1 virus were reported in the State of Tripura in India. The antigenic and genetic analyses of seven H5N1 viruses isolated during these outbreaks were carried out. Antigenic analysis confirmed 64 to 256-fold reduction in cross reactivity compared with clade 2.2 viruses. The intravenous pathogenicity index of the isolates ranged from 2.80–2.95 indicating high pathogenicity to chickens. Sequencing of all the eight gene-segments of seven H5N1 viruses isolated in these outbreaks was carried out. The predicted amino acid sequence analysis revealed high pathogenicity to chickens and susceptibility to the antivirals, amantadine and oseltamivir. Phylogenetic analyses indicated that these viruses belong to clade 2.3.2.1 and were distinct to the clade 2.3.2.1 viruses isolated in Nepal. Identification of new clade 2.3.2 H5N1 viruses in South Asia is reminiscent of the introduction of clade 2.2 viruses in this region in 2006/7. It is now important to monitor whether the clade 2.3.2.1 is replacing clade 2.2 in this region or co-circulating with it. Continued co-circulation of various subclades of the H5N1 virus which are more adapted to land based poultry in a highly populated region such as South Asia increases the risk of evolution of pandemic H5N1 strains.

The ecology and age structure of a highly pathogenic avian influenza virus outbreak in wild mute swans

The first UK epizootic of highly pathogenic (HP) H5N1 influenza in wild birds occurred in 2008, in a population of mute swans that had been the subject of ornithological study for decades. Here we use an innovative combination of ornithological, phylogenetic and immunological approaches to investigate the ecology and age structure of HP H5N1 in nature. We screened samples from swans and waterbirds using PCR and sequenced HP H5N1-positive samples. The outbreak's origin was investigated by linking bird count data with a molecular clock analysis of sampled virus sequences. We used ringing records to reconstruct the age-structure of outbreak mortality, and we estimated the age distribution of prior exposure to avian influenza. Outbreak mortality was low and all HP H5N1-positive mute swans in the affected population were <3 years old. Only the youngest age classes contained an appreciable number of individuals with no detectable antibody responses to viral nucleoprotein. Phylogenetic analysis indicated that the outbreak strain circulated locally for ~1 month before detection and arrived when the immigration rate of migrant waterbirds was highest. Our data are consistent with the hypothesis that HP H5N1 epizootics in wild swans exhibit limited mortality due to immune protection arising from previous exposure. Our study population may represent a valuable resource for investigating the natural ecology and epidemiology of avian influenza.

A qualitative approach to measure the effectiveness of active avian influenza virus surveillance with respect to its cost: A case study from Switzerland

The aim of the project was to apply cost-effectiveness analysis to the economic appraisal of avian influenza virus (AIV) surveillance, using the implemented surveillance programme in Switzerland as a case study. First a qualitative risk assessment approach was used to assess the expected impact of surveillance on the transmission and spread of AIV. The effectiveness of surveillance was expressed as the difference in defined probabilities between a scenario with surveillance and a scenario without surveillance. The following probabilities were modelled (i) transmission of highly pathogenic AIV (HPAIV) from wild birds to poultry, (ii) mutation from low pathogenic AIV (LPAIV) into HPAIV in poultry, and (iii) transmission of HPAIV to other poultry holdings given a primary outbreak.The cost-effectiveness ratio was defined conventionally as the difference in surveillance costs (ΔC) divided by the change in probability (ΔP), the technical objective, on the presumption that surveillance diminishes the respective probabilities. However, results indicated that surveillance in both wild birds and poultry was not expected to change the probabilities of primary and secondary AIV outbreaks in Switzerland. The overall surveillance costs incurred were estimated at 31,000 €/year, which, to be a rational investment of resources, must still reflect the value policy makers attribute to other benefits from having surveillance (e.g. peace of mind). The advantage of the approach adopted is that it is practical, transparent, and thus able to clarify for policy makers the key variables to be taken into account when evaluating the economic efficiency of resources invested in surveillance, prevention and intervention to exclude AIV.

Genetic characterization of low pathogenic H5N1 and co-circulating avian influenza viruses in wild mallards (Anas platyrhynchos) in Belgium, 2008

As part of a long-term wild bird monitoring programme, five different low pathogenic (LP) avian influenza viruses (AIVs) were isolated from wild mallards (subtypes H1N1, H4N6, H5N1, H5N3, and H10N7). A LP H5N1 and two co-circulating (same location, same time period) viruses were selected for full genome sequencing. An H1N1 (A/Anas platyrhynchos/Belgium/09-762/2008) and an H5N1 virus (A/Anas platyrhynchos/Belgium/09-762-P1/2008) were isolated on the same day in November 2008, then an H5N3 virus (A/Anas platyrhynchos/09-884/2008) 5 days later in December 2008. All genes of these co-circulating viruses shared common ancestors with recent (2001 to 2007) European wild waterfowl influenza viruses. The H5N1 virus shares genome segments with both the H1N1 (PB1, NA, M) and the H5N3 (PB2, HA) viruses, and all three viruses share the same NS sequence. A double infection with two different PA segments from H5N1 and from H5N3 could be observed for the H1N1 sample. The observed gene constellations resulted from multiple reassortment events between viruses circulating in wild birds in Eurasia. Several internal gene segments from these 2008 viruses and the N3 sequence from the H5N3 show homology with sequences from 2003 H7 outbreaks in Italy (LP) and the Netherlands (highly pathogenic). These data contribute to the growing sequence evidence of the dynamic nature of the avian influenza natural reservoir in Eurasia, and underline the importance of monitoring AIV in wild birds. Genetic information of potential hazard to commercial poultry continues to circulate in this reservoir, including H5 and H7 subtype viruses and genes related to previous AIV outbreaks.

Comparative Analysis of Avian Influenza Virus Diversity in Poultry and Humans during a Highly Pathogenic Avian Influenza A (H7N7) Virus Outbreak

Although increasing data have become available that link human adaptation with specific molecular changes in nonhuman influenza viruses, the molecular changes of these viruses during a large highly pathogenic avian influenza virus (HPAI) outbreak in poultry along with avian-to-human transmission have never been documented. By comprehensive virologic analysis of combined veterinary and human samples obtained during a large HPAI A (H7N7) outbreak in the Netherlands in 2003, we mapped the acquisition of human adaptation markers to identify the public health risk associated with an HPAI outbreak in poultry. Full-length hemagglutinin (HA), neuraminidase (NA), and PB2 sequencing of A (H7N7) viruses obtained from 45 human cases showed amino acid variations at different codons in HA (n=20), NA (n=23), and PB2 (n=23). Identification of the avian sources of human virus infections based on 232 farm sequences demonstrated that for each gene about 50% of the variation was already present in poultry. Polygenic accumulation and farm-to-farm spread of known virulence and human adaptation markers in A (H7N7) virus-infected poultry occurred prior to farm-to-human transmission. These include the independent emergence of HA A143T mutants, accumulation of four NA mutations, and farm-to-farm spread of virus variants harboring mammalian host determinants D701N and S714I in PB2. This implies that HPAI viruses with pandemic potential can emerge directly from poultry. Since the public health risk of an avian influenza virus outbreak in poultry can rapidly change, we recommend virologic monitoring for human adaptation markers among poultry as well as among humans during the course of an outbreak in poultry.

The Relationship between Environmental Factors and the Onsets of Avian Influenza Outbreaks in Thailand

The relationship between environmental factors and the onsets of avian influenza virus (AIV; H5N1) outbreaks in Thailand was studied. The results show that the onsets of the disease correlate with the maximum gradient of temperature and wind speed within 24 hours, density of villages in a radius of five kilometers, and distance from the last AIV outbreak area. This study also presents how meteorological conditions have an effect on the occurrence of onsets of AIV in Thailand.