Pathogenicity in domestic ducks and mice of highly pathogenic H5N1 clade 2.3.2.1 influenza viruses recently circulating in Eastern Asia

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.

Comparative susceptibility of the common teal (Anas crecca) to infection with high pathogenic avian influenza virus strains isolated in Japan in 2004-2017

High pathogenic avian influenza viruses (HPAIVs) of the H5 subtype have spread in poultry and wild birds worldwide. Current studies have highlighted the association between the migration of wild birds and the spread of HPAIVs. However, virological studies examining responsible species of migratory birds to spread HPAIVs are limited. In Japan, the common teal (Anas crecca) arrives in great numbers for overwintering every autumn-spring season; therefore, we performed experimental infection using six H5 HPAIVs isolated in past outbreaks in Japan (A/chicken/Yamaguchi/7/2004 (H5N1), A/whooper swan/Akita/1/2008 (H5N1), A/mandarin duck/Miyazaki/22M-765/2011 (H5N1), A/duck/Chiba/26-372-48/2014 (H5N8), A/duck/Hyogo/1/2016 (H5N6) and A/mute swan/Shimane/3211A002/2017 (H5N6)) to evaluate the susceptibility of the species to HPAIV infection. The results illustrated that most birds in all experimental groups were infected by the strains, and they shed viruses for a prolonged period, in trachea than cloaca, without displaying distinctive clinical signs. In addition, comparative analysis using calculation value of total viral shedding during the experiment revealed that the birds shed viruses at above a certain level regardless of the differences of strains. These results suggested that the common teal could be a migratory bird species that disseminates viruses in the environment, thereby influencing HPAI outbreaks in wild birds in Japan.

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.

Novel reassortant influenza A(H5N8) viruses among inoculated domestic and wild ducks, South Korea, 2014

An outbreak of highly pathogenic avian influenza, caused by a novel reassortant influenza A (H5N8) virus, occurred among poultry and wild birds in South Korea in 2014. The aim of this study was to evaluate the pathogenesis in and mode of transmission of this virus among domestic and wild ducks. Three of the viruses had similar pathogenicity among infected domestic ducks: the H5N8 viruses were moderately pathogenic (0%-20% mortality rate); in wild mallard ducks, the H5N8 and H5N1 viruses did not cause severe illness or death; viral replication and shedding were greater in H5N8-infected mallards than in H5N1-infected mallards. Identification of H5N8 viruses in birds exposed to infected domestic ducks and mallards indicated that the viruses could spread by contact. We propose active surveillance to support prevention of the spread of this virus among wild birds and poultry, especially domestic ducks.

Pathogenicity of H5N8 virus in chickens from Korea in 2014

In 2014, two genetically distinct H5N8 highly pathogenic avian influenza (HPAI) viruses were isolated from poultry and wild birds in Korea. The intravenous pathogenicity indices for the two representative viruses were both 3.0. Mortality of chickens intranasally inoculated with the two H5N8 viruses was 100% with a mean death times of 2.5 and 4.5 days. Mortality rates of the contact groups for the two H5N8 viruses were 33.3% and 66.6%. Our study showed that transmissibility of the novel H5N8 viruses was different from that of previously identified H5N1 HPAI viruses, possibly due to genetic changes.