Pathobiology of the highly pathogenic avian influenza viruses H7N1 and H5N8 in different chicken breeds and role of Mx 2032 G/A polymorphism in infection outcome

Highly Pathogenic Avian Influenza (HPAI) H5 Clade 2.3.4.4b Virus Infection in Birds and Mammals

Avian influenza viruses (AIVs) are highly contagious respiratory viruses of birds, leading to significant morbidity and mortality globally and causing substantial economic losses to the poultry industry and agriculture. Since their first isolation in 2013-2014, the Asian-origin H5 highly pathogenic avian influenza viruses (HPAI) of clade 2.3.4.4b have undergone unprecedented evolution and reassortment of internal gene segments. In just a few years, it supplanted other AIV clades, and now it is widespread in the wild migratory waterfowl, spreading to Asia, Europe, Africa, and the Americas. Wild waterfowl, the natural reservoir of LPAIVs and generally more resistant to the disease, also manifested high morbidity and mortality with HPAIV clade 2.3.4.4b. This clade also caused overt clinical signs and mass mortality in a variety of avian and mammalian species never reported before, such as raptors, seabirds, sealions, foxes, and others. Most notably, the recent outbreaks in dairy cattle were associated with the emergence of a few critical mutations related to mammalian adaptation, raising concerns about the possibility of jumping species and acquisition of sustained human-to-human transmission. The main clinical signs and anatomopathological findings associated with clade 2.3.4.4b virus infection in birds and non-human mammals are hereby summarized.

A case-control study of the infection risk of H5N8 highly pathogenic avian influenza in Japan during the winter of 2020-2021

In Japan, outbreaks of H5N8 highly pathogenic avian influenza (HPAI) were reported between November 2020 and March 2021 in 52 poultry farms. Understanding HPAI epidemiology would help poultry industries improve their awareness of the disease and enhance the immediate implementation of biosecurity measures. This study was a simulation-based matched case-control study to elucidate the risk factors associated with HPAI outbreaks in chicken farms in Japan. Data were collected from 42 HPAI-affected farms and 463 control farms that were within a 5-km radius of each case farm but remained uninfected. When infected farms were detected as clusters, one farm was randomly selected from each cluster, considering the possibility that the cluster was formed by farm-to-farm transmission within an epidemic area. For each case farm, up to three control farms were selected within a 5-km radius. Overall, 26 case farms (16 layer and 10 broiler farms) and 75 control farms (45 layer and 30 broiler farms) were resampled 1000 times for the conditional logistic regression model with explanatory variables comprising geographical factors and farm flock size. A larger flock size and shorter distance to water bodies from the farm were found to increase infection risk in layer farms. Similarly, in broiler farms, a shorter distance to water bodies increased infection risk. On larger farms, frequent access of farm staff and instrument carriages to premises could lead to increased infection risk. Waterfowl visiting water bodies around farms may also be associated with infection risk.

Pathogenicity of H5N8 avian influenza virus in chickens and in duck breeds and the role of MX1 and IFN-α in infection outcome and transmission to contact birds

This study examined the pathogenicity, immunogenicity, and transmission potential of the H5N8 HPAI clade 2.3.4.4b virus in three breeds of ducks and in broiler chickens. Chickens, Muscovy, Pekin, and Mallard ducks (n = 10) received a dose of 6 log10 EID50 of HPAIV H5N8 directly. Nine contact chickens were introduced to each group on the day of infection. All infected chickens died, with MDT of 7.6 days. Muscovy and Pekin ducks died by 11.1% and 10%, respectively, with MDTs of 7 and 6 days. No Mallards died but showed more severe clinical disease than Pekin ducks. Mallards had the highest MX1 gene expression in the lung and spleen and IFN-α in the spleen. MX1 expression levels were lower in the spleen and lung of Pekin ducks, in the spleen of chickens and in the lung of Muscovy ducks than in noninfected controls. However, viral shedding was higher in ducks than in chickens and was highest in Mallards. 66.7% of chickens placed in contact with infected chickens died and 77.8% of in-contact chickens to infected three duck breeds died. In conclusion, there was a diversity in sensitivity and immunogenicity for HPAIV H5N8 among duck breeds, resulting in diverse infection outcomes and transmissibility to contacts. This study provides duck/chicken interface models for HPAIV transmission to poultry.

Persistence of low pathogenic avian influenza virus in artificial streams mimicking natural conditions of waterfowl habitats in the Mediterranean climate

Avian influenza viruses (AIVs) can affect wildlife, poultry, and humans, so a One Health perspective is needed to optimize mitigation strategies. Migratory waterfowl globally spread AIVs over long distances. Therefore, the study of AIV persistence in waterfowl staging and breeding areas is key to understanding their transmission dynamics and optimizing management strategies. Here, we used artificial streams mimicking natural conditions of waterfowl habitats in the Mediterranean climate (day/night cycles of photosynthetic active radiation and temperature, low water velocity, and similar microbiome to lowland rivers and stagnant water bodies) and then manipulated temperature and sediment presence (i.e., 10-13 °C vs. 16-18 °C, and presence vs. absence of sediments). An H1N1 low pathogenic AIV (LPAIV) strain was spiked in the streams, and water and sediment samples were collected at different time points until 14 days post-spike to quantify viral RNA and detect infectious particles. Viral RNA was detected until the end of the experiment in both water and sediment samples. In water samples, we observed a significant combined effect of temperature and sediments in viral decay, with higher viral genome loads in colder streams without sediments. In sediment samples, we didn't observe any significant effect of temperature. In contrast to prior laboratory-controlled studies that detect longer persistence times, infectious H1N1 LPAIV was isolated in water samples till 2 days post-spike, and none beyond. Infectious H1N1 LPAIV wasn't isolated from any sediment sample. Our results suggest that slow flowing freshwater surface waters may provide conditions facilitating bird-to-bird transmission for a short period when water temperature are between 10 and 18 °C, though persistence for extended periods (e.g., weeks or months) may be less likely. We hypothesize that experiments simulating real environments, like the one described here, provide a more realistic approach for assessing environmental persistence of AIVs.

Myxovirus resistance (Mx) Gene Diversity in Avian Influenza Virus Infections

Avian influenza viruses (AIVs) pose threats to animal and human health. Outbreaks from the highly pathogenic avian influenza virus (HPAIV) in indigenous chickens in Bangladesh are infrequent. This could be attributed to the Myxovirus resistance (Mx) gene. To determine the impact of Mx gene diversity on AIV infections in chicken, we assessed the Mx genes, AIVs, and anti-AIV antibodies. DNA from blood cells, serum, and cloacal swab samples was isolated from non-vaccinated indigenous chickens and vaccinated commercial chickens. Possible relationships were assessed using the general linear model (GLM) procedure. Three genotypes of the Mx gene were detected (the resistant AA type, the sensitive GG type, and the heterozygous AG type). The AA genotype (0.48) was more prevalent than the GG (0.19) and the AG (0.33) genotypes. The AA genotype was more prevalent in indigenous than in commercial chickens. A total of 17 hemagglutinating viruses were isolated from the 512 swab samples. AIVs were detected in two samples (2/512; 0.39%) and subtyped as H1N1, whereas Newcastle disease virus (NDV) was detected in the remaining samples. The viral infections did not lead to apparent symptoms. Anti-AIV antibodies were detected in 44.92% of the samples with levels ranging from 27.37% to 67.65% in indigenous chickens and from 26% to 87.5% in commercial chickens. The anti-AIV antibody was detected in 40.16%, 65.98%, and 39.77% of chickens with resistant, sensitive, and heterozygous genotypes, respectively. The genotypes showed significant association (p < 0.001) with the anti-AIV antibodies. The low AIV isolation rates and high antibody prevalence rates could indicate seroconversion resulting from exposure to the virus as it circulates. Results indicate that the resistant genotype of the Mx gene might not offer anti-AIV protection for chickens.

Highly Pathogenic Avian Influenza (HPAI H5Nx, Clade 2.3.4.4.b) in Poultry and Wild Birds in Sweden: Synopsis of the 2020-2021 Season

Highly pathogenic avian influenza (HPAI, Gs/Gd lineage) was introduced to Europe in 2005 and has since caused numerous outbreaks in birds. The 2020-2021 season was the hitherto most devastating when considering bird numbers and duration in Europe. Surveillance data, virologic results and epidemiologic investigations from the 2020-2021 outbreaks in Sweden were analysed. Subtypes H5N8 and H5N5 were detected on 24 farms with poultry or other captive birds. In wild birds, subtypes H5N8, H5N5, H5N1, H5N4, H5Nx were detected in 130 out of 811 sampled birds. There was a spatiotemporal association between cases in wild birds and poultry. Based on phylogeny and epidemiology, most of the introductions of HPAI to commercial poultry were likely a result of indirect contact with wild birds. A definite route of introduction to poultry could not be established although some biosecurity breaches were observed. No spread between farms was identified but airborne spread between flocks on the same farm was suspected. Our findings exemplify the challenges posed by the continuously changing influenza viruses that seem to adapt to a broader species spectrum. This points to the importance of wild bird surveillance, compliance to biosecurity, and identification of risk factors for introduction on poultry farms.

Dual Host and Pathogen RNA-Seq Analysis Unravels Chicken Genes Potentially Involved in Resistance to Highly Pathogenic Avian Influenza Virus Infection

Highly pathogenic avian influenza viruses (HPAIVs) cause severe systemic disease and high mortality rates in chickens, leading to a huge economic impact in the poultry sector. However, some chickens are resistant to the disease. This study aimed at evaluating the mechanisms behind HPAIV disease resistance. Chickens of different breeds were challenged with H7N1 HPAIV or clade 2.3.4.4b H5N8 HPAIV, euthanized at 3 days post-inoculation (dpi), and classified as resistant or susceptible depending on the following criteria: chickens that presented i) clinical signs, ii) histopathological lesions, and iii) presence of HPAIV antigen in tissues were classified as susceptible, while chickens lacking all these criteria were classified as resistant. Once classified, we performed RNA-Seq from lung and spleen samples in order to compare the transcriptomic signatures between resistant and susceptible chickens. We identified minor transcriptomic changes in resistant chickens in contrast with huge alterations observed in susceptible chickens. Interestingly, six differentially expressed genes were downregulated in resistant birds and upregulated in susceptible birds. Some of these genes belong to the NF-kappa B and/or mitogen-activated protein kinase signaling pathways. Among these six genes, the serine protease-encoding gene PLAU was of particular interest, being the most significantly downregulated gene in resistant chickens. Expression levels of this protease were further validated by RT-qPCR in a larger number of experimentally infected chickens. Furthermore, HPAIV quasi-species populations were constructed using 3 dpi oral swabs. No substantial changes were found in the viral segments that interact with the innate immune response and with the host cell receptors, reinforcing the role of the immune system of the host in the clinical outcome. Altogether, our results suggest that an early inactivation of important host genes could prevent an exaggerated immune response and/or viral replication, conferring resistance to HPAIV in chickens.

Different Sensitivity of Japanese Native-Bred Chickens to H5 Subtypes of Highly Pathogenic Avian Influenza Viruses

The aim of this study was to investigate the sensitivity of three breeds of Japanese native chickens, commercial broilers, and specific-pathogen-free (SPF) white leghorns to three strains of the H5 subtype of highly pathogenic avian influenza viruses (HPAIVs). Chickens were experimentally inoculated with doses of 10², 10⁴, and 10⁶ 50% egg infective dose of A/mandarin duck/Miyazaki/22M-765/2011 (duck-11), A/chicken/Miyazaki/7/2014 (chicken-14), and A/chicken/Kumamoto/1-2C/2016 (chicken-16). The 50% chicken lethal dose of each virus, mean death time, and viral shedding patterns were compared. The Japanese native chickens showed varied susceptibility to the three H5 HPAIV isolates. Although two of the breeds showed some degree of resistance to duck-11 and chicken-14, all three were more sensitive to chicken-16 than commercial broiler chickens. We have shown that Japanese native chickens do not necessarily have resistance to HPAIV and that the pathogenic characteristics of HPAIVs are quite different between native and commercial chickens.