Susceptibility of Pigeons to Clade 1 and 2.2 High Pathogenicity Avian Influenza H5N1 Virus

Overview of avian influenza virus in urban feral pigeons in Bangkok, Thailand

This survey assessed the presence of avian influenza virus (AIV) in urban feral pigeons (UFPs) in Bangkok, Thailand. A total of 485 UFPs were collected from eight study sites, and blood, tracheal, and cloacal samples were collected from each bird. Virus isolation and molecular methods did not detect AIV in any of the birds tested. A hemagglutination inhibition test was used to test for antibodies to high and low pathogenicity AIV subtypes. AIV subtype H9 antibodies were the only antibodies detected. The overall seroprevalence of AIV subtype H9 antibodies was 6.9%, and subtype H9 antibodies were found in UFPs at all eight sites. The overall geometric mean titer was 11.07 (range: 8-64). These results reveal that UFPs in Bangkok do not currently pose a risk of transmitting AIV to humans. However, monitoring of AIV in UFPs is necessary for disease control and to minimize the possibility of influenza outbreaks.

Subclinical Infection and Transmission of Clade 2.3.4.4 H5N6 Highly Pathogenic Avian Influenza Virus in Mandarin Duck (Aix galericulata) and Domestic Pigeon (Columbia livia domestica)

Since 2014, H5Nx clade 2.3.4.4 highly pathogenic avian influenza viruses (HPAIV) have caused outbreaks in wild birds and poultry in multiple continents, including Asia, Europe, Africa, and North America. Wild birds were suspected to be the sources of the local and global spreads of HPAIV. This study evaluated the infectivity, pathogenicity, and transmissibility of clade 2.3.4.4 H5N6 HPAIV in mandarin ducks (Aixgalericulata) and domestic pigeons (Columbia livia domestica). None of the birds used in this study, 20 mandarin ducks or 8 pigeons, showed clinical signs or mortality due to H5N6 HPAI infection. Two genotypes of H5N6 HPAIV showed replication and transmission by direct and indirect contact between mandarin ducks. H5N6 HPAIV replicated and transmitted by direct contact between pigeons, although the viral shedding titer and duration were relatively lower and shorter than those in mandarin ducks. Influenza virus antigen was detected in various internal organs of infected mandarin ducks and pigeons, indicating systemic infection. Therefore, our results indicate mandarin ducks and pigeons can be subclinically infected with clade 2.3.4.4 H5N6 HPAIV and transfer the virus to adjacent birds. The role of mandarin ducks and pigeons in the spread and prevalence of clade 2.3.4.4 H5N6 viruses should be carefully monitored.

Infectivity and pathobiology of H7N1 and H5N8 high pathogenicity avian influenza viruses for pigeons (Columba livia var. domestica)

Avian influenza (AI) is one of the most important viral diseases in poultry, wildlife and humans. Available data indicate that pigeons play a minimum role in the epidemiology of AI. However, a degree of variation exists in the susceptibility of pigeons to highly pathogenic AI viruses (HPAIVs), especially since the emergence of the goose/Guangdong H5 lineage. Here, the pathogenesis of H5N8 HPAIV in comparison with a H7N1 HPAIV and the role of pigeons in the epidemiology of these viruses were evaluated. Local and urban pigeons (Columba livia var. domestica) were intranasally inoculated with 10⁵ ELD₅₀ of A/goose/Spain/IA17CR02699/2017 (H5N8) or A/Chicken/Italy/5093/1999 (H7N1) and monitored during 14 days. Several pigeons inoculated with H5N8 or H7N1 seroconverted. However, clinical signs, mortality, microscopic lesions and viral antigen were only detected in a local pigeon inoculated with H5N8 HPAIV. This pigeon presented prostration and neurological signs that correlated with the presence of large areas of necrosis and widespread AIV antigen in the central nervous system, indicating that the fatal outcome was associated with neurological dysfunction. Viral RNA in swabs was detected in some pigeons inoculated with H7N1 and H5N8, but it was inconsistent, short-term and at low titres. The present study demonstrates that the majority of pigeons were resistant to H5N8 and H7N1 HPAIVs, despite several pigeons developing asymptomatic infections. The limited viral shedding indicates a minimum role of pigeons as amplifiers of HPAIVs, regardless of the viral lineage, and suggests that this species may represent a low risk for environmental contamination. RESEARCH HIGHLIGHTS H7N1 and H5N8 HPAIVs can produce subclinical infections in pigeons. The mortality caused by H5N8 HPAIV in one pigeon was associated with neurological dysfunction. Pigeons represent a low risk for environmental contamination by HPAIVs.

Investigation of Avian Influenza Viruses (H9N2-H5nx) in Pigeons during Highly Pathogenic Avian Influenza Outbreaks in Iran, in 2016

Avian influenza (AI) virus (H9N2 and H5 subtypes) infections in birds cause major concerns around the world. The majority of the avian species, such as domestic, pet, and wild birds, are natural and experimental hosts of avian influenza viruses. There are global concerns about members of the Columbidae family, namely pigeons or doves, for their role as the potential interspecies bridge in influenza A viruses ecology. The acquired scientific data in this regard is still not clear since there are doubts about whether or not they transmit viruses between susceptible populations, and spread viruses among farms during outbreaks. To monitor H5 and H9 influenza virus infection status in the rural, backyard, and domestic birds, an annual active surveillance program was performed from September to October 2016. In December 2016, an outbreak of highly pathogenic avian influenza (HPAI) virus subtype H5N8 was detected in a layer farm in Tehran province, Iran. The present research was conducted to study H9N2 or H5 infections in pigeons within HPAI H5N8 2016 outbreaks and annual national AI surveillance in Iran. For this purpose, cloacal swabs and tissue samples (trachea, lung, brain, liver, heart, pancreas, and cecal tonsil) were collected and examined by real-time reverse transcription-polymerase chain reaction (RT-PCR) method and virus isolation. Results of the tests performed on the swab and tissue samples were negative for H5 nor H9N2 viruses. The samples in real-time RT-PCR that after three passages still showed negative results in HA and molecular tests were considered negative. Moreover, the Newcastle disease virus was isolated in most of the samples taken from dead pigeons, after inoculation in embryonated chicken eggs.

Pattern Recognition Receptor Signaling and Innate Responses to Influenza A Viruses in the Mallard Duck, Compared to Humans and Chickens

Mallard ducks are a natural host and reservoir of avian Influenza A viruses. While most influenza strains can replicate in mallards, the virus typically does not cause substantial disease in this host. Mallards are often resistant to disease caused by highly pathogenic avian influenza viruses, while the same strains can cause severe infection in humans, chickens, and even other species of ducks, resulting in systemic spread of the virus and even death. The differences in influenza detection and antiviral effectors responsible for limiting damage in the mallards are largely unknown. Domestic mallards have an early and robust innate response to infection that seems to limit replication and clear highly pathogenic strains. The regulation and timing of the response to influenza also seems to circumvent damage done by a prolonged or dysregulated immune response. Rapid initiation of innate immune responses depends on viral recognition by pattern recognition receptors (PRRs) expressed in tissues where the virus replicates. RIG-like receptors (RLRs), Toll-like receptors (TLRs), and Nod-like receptors (NLRs) are all important influenza sensors in mammals during infection. Ducks utilize many of the same PRRs to detect influenza, namely RIG-I, TLR7, and TLR3 and their downstream adaptors. Ducks also express many of the same signal transduction proteins including TBK1, TRIF, and TRAF3. Some antiviral effectors expressed downstream of these signaling pathways inhibit influenza replication in ducks. In this review, we summarize the recent advances in our understanding of influenza recognition and response through duck PRRs and their adaptors. We compare basal tissue expression and regulation of these signaling components in birds, to better understand what contributes to influenza resistance in the duck.

Molecular identification of avian influenza virus subtypes H5N1 and H9N2 in birds from farms and live bird markets and in respiratory patients

Background

Avian influenza viruses (AIVs) have been endemic in Egypt since 2006, and the co-circulation of high-pathogenic avian influenza H5N1 and low-pathogenic avian influenza H9N2 subtypes in poultry has been reported; therefore, Egypt is considered a hotspot for the generation of new subtypes and genotypes. We aimed to characterize AIVs circulating on commercial farms and in live bird markets (LBMs) during the winters of 2015 and 2016 in the study area and to identify H5N1 and H9N2 viruses in respiratory patients.

Methods

In total, 159 samples were collected from ducks, pigeons and quails on farms (n = 59) and in LBMs (n = 100) and screened by real-time RT-PCR for H5N1 and H9N2 subtypes. Clinical and postmortem examination was carried out on birds from the farms. Positive H5N1 samples were sequenced and analysed for mutations. Tracheal swabs were also collected from 89 respiratory patients admitted to respiratory hospitals in the same study area.

Results

Overall, H5N1 was identified in 13.6% of birds from farms, while it was detected in 17% of birds in LBMs. Subtype H9N2 was only identified from pigeons on farms (6.5%) and LBMs (11.4%). Sequencing of the haemagglutination gene (HA) in nine representative H5N1 isolates revealed a multi-basic amino acid motif at the cleavage site (321-PQGEKRRKKR/GLF-333), which is characteristic of highly pathogenic AIV, in five of our isolates, while the other four isolates showed an amino acid substitution (Q322K) at this cleavage site to make it (321-P K GEKRRKKR/GLF-333). All the isolates belonged to clade 2.2.1.2, and a comparison of HA sequences at the amino acid level showed 98.8-100% homology among the nine isolates, while they showed 94.1-96.1% identity with reference strains and the commonly used vaccine strain in Egypt. Out of 89 respiratory patients, 3.4% were positive for H5N1 and no patients were positive for H9N2.

Discussion

Our results indicated the circulation of the endemic H5N1 and H9N2 viruses among poultry in 2015 and 2016. Birds on farms and in LBMs are reservoirs playing a role in the dissemination of the virus and producing a public health risk. The application of proper hygienic measures in farms and LBMs to control the exposure of birds and humans to the source of infection along with continuous monitoring of the circulating viruses will provide information on understanding the evolution of the viruses for vaccine studies.

Identification of polymerase gene mutations that affect viral replication in H5N1 influenza viruses isolated from pigeons

Highly pathogenic avian influenza virus H5N1 infects a wide range of host species, with a few cases of sporadic pigeon infections reported in the Middle East and Asia. However, the role of pigeons in the ecology and evolution of H5N1 viruses remains unclear. We previously reported two H5N1 virus strains, isolated from naturally infected pigeons in Egypt, that have several unique mutations in their viral polymerase genes. Here, we investigated the effect of these mutations on H5N1 polymerase activity and viral growth and identified three mutations that affected viral polymerase activity. The results showed that the PB1-V3D mutation significantly decreased polymerase activity and viral growth in both mammalian and avian cells. In contrast, the PB2-K627E and PA-K158R mutations had moderate effects: PB2-K627E decreased and PA-K158R increased polymerase activity. Structural homology modelling indicated that the PB1-V3D residue was located in the PB1 core region that interacts with PA, predicting that the PB1 mutation would produce a stronger interaction between PB1 and PA that results in decreased replication of pigeon-derived H5N1 viruses. Our results identified several unique mutations responsible for changes in polymerase activity in H5N1 virus strains isolated from infected pigeons, emphasizing the importance of avian influenza surveillance in pigeons and in studying the possible role of pigeon-derived H5N1 viruses in avian influenza virus evolution.

Pigeons are resistant to experimental infection with H7N9 avian influenza virus

To determine the susceptibility of pigeons to the newly emerged avian influenza virus subtype H7N9, we experimentally infected three different types of pigeons (meat, town, and racing) with two different doses (2 × 10(4) or 2 × 10(5) EID50) of H7N9 avian influenza virus A/Chicken/China/2013 by either intranasal and intraocular inoculation (IN + IO) or intravenous injection (IV). In addition, the potential transmission of H7N9 to pigeons by direct close contact with experimentally infected pigeons and chickens was assessed. Results showed that none of the experimentally infected pigeons exhibited any clinical signs regardless of the infection route and dose. Of the 12 racing pigeons that were randomly selected and necropsied, none of them had any gross lesions. In agreement with this finding, virus was not isolated from all pigeons. No detectable H7-specific antibodies were found in any pigeon. In contrast, 11 of 31 chickens that were either directly infected with H7N9 by IN + IO inoculation or by contact with IN + IO-infected chickens had conjunctivitis. Virus was isolated from all 31 chickens and H7-specific antibodies were detected in these chickens. However, none of the IV-infected chickens or chickens in direct contact with IV-infected chickens had any clinical signs. No virus was isolated from these chickens and no H7-specific antibody was detected. Overall, we conclude that pigeons are less or not susceptible to the H7N9 virus at the doses used and are not likely to serve as a reservoir for the virus. However, the virus does cause conjunctivitis in chickens and can transmit to susceptible hosts by direct contact.

The response of mute swans (Cygnus olor, Gm. 1789) to vaccination against avian influenza with an inactivated H5N2 vaccine

Background

Recent epidemics of highly pathogenic avian influenza (HPAI) produced an unprecedented number of cases in mute swans (Cygnus olor) in European countries, which indicates that these birds are very sensitive to the H5N1 virus. The HPAI outbreaks stirred a debate on the controversial stamping-out policy in populations of protected bird species. After preventive vaccination had been approved in the European Union, several countries have introduced vaccination schemes to protect poultry, captive wild birds or exotic birds in zoos against HPAI. The aim of this study was to investigate the immune response of wild mute swans to immunization with an inactivated AI H5N2 vaccine approved for use in poultry. The serological responses of mute swans were assessed by comparison with racing pigeons (Columba livia), a species which is characterized by different susceptibility to infection with the H5N1 HPAI virus and plays a questionable role in the ecology of influenza (H5N1) viruses.

Results

Swans were vaccinated once or twice at an interval of 4 weeks. The humoral immune response was evaluated by hemagglutination inhibition (HI) and NP-ELISA. The lymphocyte blast transformation test was used to determine the cell-mediated immune response. Higher values of the geometric mean titer (GMT) and 100 % seroconversion (HI ≥32) were noted in double vaccinated swans (1448.2) than in single vaccinated swans (128.0) or in double vaccinated pigeons (215.3). Significant differences in HI titers were observed between swans and pigeons, but no variations in ELISA scores were noted after the booster dose. Immunization of swans had no effect on the proliferative activity of lymphocytes.

Conclusions

The inactivated H5N2 vaccine was safe and immunogenic for mute swans and pigeons. Vaccination may have practical implications for swans kept in zoos, wildlife parks or rehabilitation centers. However, challenge studies are needed to prove the efficacy of the H5N2 AI vaccine.