Infectivity and transmissibility of H9N2 avian influenza virus in chickens and wild terrestrial birds

Prevalence and diversity of H9N2 avian influenza in chickens of Northern Vietnam, 2014

Despite their classification as low pathogenicity avian influenza viruses (LPAIV), A/H9N2 viruses cause significant losses in poultry in many countries throughout Asia, the Middle East and North Africa. To date, poultry surveillance in Vietnam has focused on detection of influenza H5 viruses, and there is limited understanding of influenza H9 epidemiology and transmission dynamics. We determined prevalence and diversity of influenza A viruses in chickens from live bird markets (LBM) of 7 northern Vietnamese provinces, using pooled oropharyngeal swabs collected from October to December 2014. Screening by real time RT-PCR revealed 1207/4900 (24.6%) of pooled swabs to be influenza A virus positive; overall prevalence estimates after accounting for pooling (5 swabs/pools) were 5.8% (CI 5.4–6.0). Subtyping was performed on 468 pooled swabs with M gene Ct < 26. No influenza H7 was detected; 422 (90.1%) were H9 positive; and 22 (4.7%) were H5 positive. There was no evidence was of interaction between H9 and H5 virus detection rates. We sequenced 17 whole genomes of A/H9N2, 2 of A/H5N6, and 11 partial genomes. All H9N2 viruses had internal genes that clustered with genotype 57 and were closely related to Chinese human isolates of A/H7N9 and A/H10N8. Using a nucleotide divergence cutoff of 98%, we identified 9 distinct H9 genotypes. Phylogenetic analysis suggested multiple introductions of H9 viruses to northern Vietnam rather than in-situ transmission. Further investigations of H9 prevalence and diversity in other regions of Vietnam are warranted to assess H9 endemicity elsewhere in the country.

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We report detection of highly pathogenic avian influenza (HPAI) from healthy chickens in Live Bird Markets of Vietnam. Because all breeds of domestic chickens are extremely susceptible to HPAI, we speculate that HPAI detections from market chickens may reflect infections that occur after arrival in the market. Alternatively, shedding of HPAI from healthy birds may reflect vaccine-induced protective immunity that mitigates disease but does not block viral infection.

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As many as 49% of all pooled surveillance swabs were positive for influenza A virus, corresponding to an overall Influenza A prevalence of 5.45% (95% Confidence Interval 5.4-6.0%).

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Low pathogenicity avian influenza (LPAI) H9N2 accounted for the vast majority of all influenza A detections in market chickens sampled from 9 northern provinces.

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To date there is no evidence to suggest an interaction effect between circulation of H5 and H9 viruses; however sampling strategies that involve pooling of surveillance swabs from multiple birds greatly complicates the assessment of co-infection rates or evaluation of epidemiological associations.

Host genetics determine susceptibility to avian influenza infection and transmission dynamics

Host-genetic control of influenza virus infection has been the object of little attention. In this study we determined that two inbred lines of chicken differing in their genetic background , Lines 0 and C-B12, were respectively relatively resistant and susceptible to infection with the low pathogenicity influenza virus A/Turkey/England/647/77 as defined by substantial differences in viral shedding trajectories. Resistant birds, although infected, were unable to transmit virus to contact birds, as ultimately only the presence of a sustained cloacal shedding (and not oropharyngeal shedding) was critical for transmission. Restriction of within-bird transmission of virus occurred in the resistant line, with intra-nares or cloacal infection resulting in only local shedding and failing to transmit fully through the gastro-intestinal-pulmonary tract. Resistance to infection was independent of adaptive immune responses, including the expansion of specific IFNγ secreting cells or production of influenza-specific antibody. Genetic resistance to a novel H9N2 virus was less robust, though significant differences between host genotypes were still clearly evident. The existence of host-genetic determination of the outcome of influenza infection offers tools for the further dissection of this regulation and also for understanding the mechanisms of influenza transmission within and between birds.

Species difference in ANP32A underlies influenza A virus polymerase host restriction

Influenza pandemics occur unpredictably when zoonotic influenza viruses with novel antigenicity acquire the ability to transmit amongst humans ¹. Incompatibilities between avian virus components and the human host limit host range breaches. Barriers include receptor preference, virion stability and poor activity of the avian virus RNA-dependent RNA polymerase in human cells ². Mutants of the heterotrimeric viral polymerase components, particularly PB2 protein, are selected during mammalian adaptation, but their mode of action is unknown ^3–6. We show that a species-specific difference in host protein ANP32A accounts for the suboptimal function of avian virus polymerase in mammalian cells. Avian ANP32A possesses an additional 33 amino acids between the LRR and LCAR domains. In mammalian cells, avian ANP32A rescued the suboptimal function of avian virus polymerase to levels similar to mammalian adapted polymerase. Deletion of the avian-specific sequence from chicken ANP32A abrogated this activity whereas its insertion into human ANP32A, or closely related ANP32B, supported avian virus polymerase function. Substitutions, such as PB2 E627K, rapidly selected upon infection of humans with avian H5N1 or H7N9 influenza viruses, adapt the viral polymerase for the shorter mammalian ANP32A. Thus ANP32A represents an essential host partner co-opted to support influenza virus replication and is a candidate host target for novel antivirals.

Changing risk awareness and personal protection measures for low to high pathogenic avian influenza in live-poultry markets in Taiwan, 2007 to 2012

Background

Outbreaks of low and high pathogenic avian influenza (LPAI, HPAI) H5N2 in chickens have occurred in Taiwan since 2003 and 2012, respectively. Fully understanding the different awareness, attitudes and protective behaviors adopted by workers in live-poultry markets (LPMWs) and local community residents (CRs) to face the challenges of LPAI and HPAI is very important to minimize viral adaptations to human populations.

Methods

A structural questionnaire containing information on respondents’ occupation, personal risk awareness, attitudes toward different policies, and preventative measures was administered. The two-stage survey (before and after HPAI H5N2 outbreaks) was conducted from 2007 to 2012, including: (1) 430 LPMWs and 418 CRs at LPMs from different geographical areas of Taiwan after the government announced outbreaks of LPAI H5N2 during 2007–2009, and (2) 73 LPMWs and 152 CRs at two LPMs in central Taiwan after the HPAI H5N2 outbreaks in 2012. The chi-squared test and logistic regression were applied for univariate and multivariate analyses, respectively.

Results

Before HPAI-H5N2 outbreaks, higher educated respondents demonstrated greater risk awareness and concerns regarding AI. However, LPM-workers protected themselves less from AI viruses (AIVs) and had lower acceptance of human or avian influenza vaccines. Most importantly, the participants who opposed (versus agreed with) the policy on banning live-poultry slaughtering at LPMs reported lower awareness of government prevention and control policies [Odds Ratio (OR): 0.76, 95 % Confidence Interval (CI): 0.56–1.01] or practiced preventive measures (OR: 0.42, 95 % CI: 0.25–0.70).

After HPAI-H5N2 outbreaks, the risk awareness about AI in central Taiwan significantly increased [LPAI to HPAI LPMWs: 34.6 to 65.6 %, p < 0.05; CRs: 44.0 to 76.5 %, p < 0.05] and LPMWs’ belief in the effectiveness of vaccination to prevent human or avian influenza virus infection strikingly decreased (92.3 to 68.5 %, p < 0.05).

Conclusions

Risk awareness depends on high or low pathogenicity of AIVs, working in LPMs, levels of education, age, and proximity to the sites of severe AI outbreaks. Regardless of novel LPAI or HPAI virus reassortants that pose public health risks, prompt and clear risk communication focusing on both correct information about AIVs and the most appropriate preventive measures are important for effective prevention of human infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-015-0987-8) contains supplementary material, which is available to authorized users.

Practical aspects of vaccination of poultry against avian influenza virus

Although little has changed in vaccine technology for avian influenza virus (AIV) in the past 20 years, the approach to vaccination of poultry (chickens, turkeys and ducks) for avian influenza has evolved as highly pathogenic AIV has become endemic in several regions of the world. Vaccination for low pathogenicity AIV is also becoming routine in regions where there is a high level of field challenge. In contrast, some countries will not use vaccination at all and some will only use it on an emergency basis during eradication efforts (i.e. stamping-out). There are pros and cons to each approach and, since every outbreak situation is different, no one method will work equally well in all situations. Numerous practical aspects must be considered when developing an AIV control program with vaccination as a component, such as: (1) the goals of vaccination must be defined; (2) the population to be vaccinated must be clearly identified; (3) there must be a plan to obtain and administer good quality vaccine in a timely manner and to achieve adequate coverage with the available resources; (4) risk factors for vaccine failure should be mitigated as much as possible; and, most importantly, (5) biosecurity must be maintained as much as possible, if not enhanced, during the vaccination period.

An active serological survey of antibodies to newcastle disease and avian influenza (H9N2) viruses in the unvaccinated backyard poultry in Bushehr province,Iran, 2012-2013

OBJECTIVE

To test the antibodies against newcastle disease virus (NDV) and avian influenza virus (AIV, H9N2) in the unvaccinated backyard poultry in Bushehr province, Iran from 2012 to 2013.

METHODS

A total of 1 530 blood samples from unvaccinated backyard chickens in Bushehr province, south of Iran, were tested for antibodies against NDV and AIV (H9N2) by hemagglutination inhibition test according to International Epizootic Office (OIE) recommendation.

RESULTS

Of these, 614 (40.13%) and 595 (39.00%) were positive for NDV and AIV (H9N2) respectively.

CONCLUSIONS

The findings of the present study indicated that NDV and AIV (H9N2) were endemic and widely distributed in backyard areas of Bushehr province which should be incorporated in the control strategies. Further studies are needed to identify the circulating virus genotypes, model their transmission risk, provide adapted control measures and design proper and applicable vaccination program.

Characterization of the amantadine-resistant H5N1 highly pathogenic avian influenza variants isolated from quails in Southern China

Highly pathogenic H5N1 avian influenza viruses have spread in poultry and wild birds in Asia, Europe, and Africa since 2003. To evaluate the role of quails in the evolution of influenza A virus, we characterized three H5N1 viruses isolated from quails (QA viruses) in southern China. Phylogenetic analysis indicated that three QA viruses derived from the A/goose/Guangdong/1/96-like lineage and most closely related to HA clade 4 A/chicken/Hong Kong/31.4/02-like viruses. Molecular analysis suggested that QA viruses and clade 4 H5N1 viruses carried consistent residue signatures, such as the characteristic M2 Ser31Asn amantadine-resistance mutation, implying a common origin of these viruses. As revealed by viral pathogenicity tests, these QA viruses could replicate in intranasally infected mice, but were not lethal to them, showing low pathogenicity in mammals. However, they killed all intravenously inoculated chickens, showing high pathogenicity in poultry. Results from amantadine sensitivity tests of wild-type QA viruses and their reverse genetic viruses demonstrated that all QA viruses were resistant to amantadine, and the M2 Ser31Asn mutation was determined as the most likely cause of the increased amantadine-resistance of H5N1 QA viruses. Our study confirmed experimentally that the amino acid at residue 31 in the M2 protein plays a major role in determining the amantadine-resistance phenotype of H5N1 influenza viruses. Our findings provide further evidence that quails may play important roles in the evolution of influenza A viruses, which raises concerns over possible transmissions of H5N1 viruses among poultry, wild birds, and humans.

Surveillance of influenza viruses in waterfowl used as decoys in Andalusia, Spain

A longitudinal study was carried out to determine the seroprevalence of avian influenza viruses (AIVs) in waterfowl used as decoys in Andalusia, southern Spain. A total of 2319 aquatic birds from 193 flocks were analyzed before and after the hunting season 2011-2012. In the first sampling, 403 out of 2319 (18.0%, CI95%: 15.8-19.0) decoys showed antibodies against AIVs by ELISA. The AI seroprevalence was significantly higher in geese (21.0%) than in ducks (11.7%) (P<0.001). Besides, the spatial distribution of AIVs was not homogeneous as significant differences among regions were observed. The prevalence of antibodies against AIVs subtypes H5 and H7 were 1.1% and 0.3%, respectively, using hemagglutination inhibition test (HI). The overall and H5 seroprevalences slightly increased after the hunting period (to 19.2% and 1.4%, respectively), while the H7 seroprevalence remained at the same level (0.3%). The proportion of flocks infected by AIVs was 65.3%, while 11.2% and 4.9% of flocks were positive for H5 and H7, respectively. Viral shedding was not detected in any of the 47 samples positive by both ELISA and HI, tested by RRT-PCR. The individual incidence after the hunting season was 3.4%. The fact that 57 animals seroconverted, 15 of which were confirmed by HI (12 H5 and 3 H7), was indication of contact with AIVs during the hunting period. The results indicate that waterfowl used as decoys are frequently exposed to AIVs and may be potentially useful as sentinels for AIVs monitoring. The seroprevalence detected and the seropositivity against AIVs H5 and H7, suggest that decoys can act as reservoirs of AIVs, which may be of animal and public health concern.