Vaccination of poultry against highly pathogenic avian influenza - part 1. Available vaccines and vaccination strategies

Several vaccines have been developed against highly pathogenic avian influenza (HPAI), mostly inactivated whole-virus vaccines for chickens. In the EU, one vaccine is authorised in chickens but is not fully efficacious to stop transmission, highlighting the need for vaccines tailored to diverse poultry species and production types. Off-label use of vaccines is possible, but effectiveness varies. Vaccines are usually injectable, a time-consuming process. Mass-application vaccines outside hatcheries remain rare. First vaccination varies from in-ovo to 6 weeks of age. Data about immunity onset and duration in the target species are often unavailable, despite being key for effective planning. Minimising antigenic distance between vaccines and field strains is essential, requiring rapid updates of vaccines to match circulating strains. Generating harmonised vaccine efficacy data showing vaccine ability to reduce transmission is crucial and this ability should be also assessed in field trials. Planning vaccination requires selecting the most adequate vaccine type and vaccination scheme. Emergency protective vaccination is limited to vaccines that are not restricted by species, age or pre-existing vector-immunity, while preventive vaccination should prioritise achieving the highest protection, especially for the most susceptible species in high-risk transmission areas. Model simulations in France, Italy and The Netherlands revealed that (i) duck and turkey farms are more infectious than chickens, (ii) depopulating infected farms only showed limitations in controlling disease spread, while 1-km ring-culling performed better than or similar to emergency preventive ring-vaccination scenarios, although with the highest number of depopulated farms, (iii) preventive vaccination of the most susceptible species in high-risk transmission areas was the best option to minimise the outbreaks' number and duration, (iv) during outbreaks in such areas, emergency protective vaccination in a 3-km radius was more effective than 1- and 10-km radius. Vaccine efficacy should be monitored and complement other surveillance and preventive efforts.

Exploring the responses of smallscale poultry keepers to avian influenza regulations and guidance in the United Kingdom, with recommendations for improved biosecurity messaging

Understanding how smallscale ('backyard') poultry keepers interpret and respond to governmental directives designed to reduce the transmission of highly pathogenic avian influenza (HPAI) is of paramount importance in preparing for future HPAI outbreaks. Qualitative insights from open questions in an online survey conducted during the 2021-22 HPAI season (1,559 responses) shed light on smallscale poultry keepers' understanding of, and responses to, governmental directives to control HPAI exposure and onwards transmission. A follow-up participatory workshop (21 participants) explored the HPAI-related information sources used by smallscale poultry keepers, their trust in these sources, perceptions of HPAI-related risk, and interpretation of, opinions on and adherence to government regulations and communications regarding biosecurity and housing measures. This paper draws on a multi-scale behaviour change model to explore barriers to compliance with HPAI-related regulations. Insights from behaviour settings theory reveal how poultry-keeping settings and routines might be 'disrupted' and 're-configured' to improve long-term biosecurity and reduce the risk of HPAI exposure. The findings highlight the need for HPAI-related guidance that is tailored to smallscale poultry keepers. This guidance should include clear action points and simple, practical, affordable and sustainable suggestions for improving compliance with biosecurity measures.

Public health response to outbreaks of highly pathogenic avian influenza (H5N1) among poultry in Northeast of Ireland, November 2021 to January 2022

OBJECTIVES

Human infections from highly pathogenic avian influenza (HPAI) H5N1 are associated with significant morbidity and mortality internationally. This study aimed to use routinely available data to examine key strategies to prevent H5N1 transmission to humans during outbreaks in poultry in residents in Cavan, Louth, Meath and Monaghan.

STUDY DESIGN

This was a cross-sectional based study.

METHODS

Data were obtained from Health Protection Team in the Department of Public Health, HSE North East and Department of Agriculture, Food, and the Marine (DAFM). Data entry and analyses were conducted using Microsoft Excel 2016.

RESULTS

The public health response focussed on contact tracing, monitoring and follow-up for household, farm workers and DAFM staff exposed on the affected farms. A total of 157 contact episodes were identified. Contacts received advice about active monitoring from their last exposure. A total of 111 (80%) were recommended chemoprophylaxis for exposure to HPAI H5N1. During the active monitoring period, two contacts developed acute respiratory symptoms, and parainfluenza 3 and rhino/enterovirus were identified in these individuals, respectively.

CONCLUSIONS

The findings of this study, using routinely gathered data, highlighted that collaboration between public health and DAFM at regional and national levels was key to rapid response to these outbreaks of HPAI in domesticated poultry. In addition, the public health response appears to have been successful in preventing H5N1 transmission from domesticated birds to humans.

Improvement of a recombinant avian avulavirus serotype 10 vectored vaccine by the addition of untranslated regions

BACKGROUND

We have previously developed a recombinant avian avulavirus serotype 10 (rAAvV-10/HA) expressing the hemagglutinin (HA) gene of a highly pathogenic avian influenza virus (HPAIV) as an emergency vaccine for poultry. rAAvV-10/HA can overcome the activity of the anti-AAvV-1 (Newcastle disease virus) antibody acquired by commercial chickens upon routine vaccination. Most chickens do not have the anti-AAvV-10 antibody, which could interfere with the vaccine efficacy. However, the vaccine efficacy of rAAvV-10/HA is not satisfactory in chickens even though it affords protection against an HPAIV challenge. In the present study, we improved the rAAvV-10/HA vaccine by enhancing the expression of the exogenous HA protein.

METHODS

The 5' and 3' untranslated regions (UTR) of each AAvV-10 gene were flanked with the exogenous HA gene cassette to modify rAAvV-10/HA, yielding different rAAv10-UTRs. As a control, rAAv10-nonUTR that did not contain any UTRs was generated. The effects of UTRs on mRNA transcription, HA protein expression, and vaccine efficacy were then examined using embryonated chicken eggs and white leghorn chickens.

RESULTS

The proportion of the HA gene mRNA among the vector-derived mRNAs (1.55-1.84-fold increase vs. the control) and HA protein levels (148-1151-fold increase vs. the control) in cells infected with rAAv10-UTRs were higher than in those infected with rAAv10-nonUTR. In vivo, vaccination of chickens with rAAv10-UTRs resulted in 100% protection against an HPAIV challenge. No chickens vaccinated with rAAv10-NP-UTR, rAAv10-F-UTR, or rAAv10-HN-UTR shed the virus in the throat and cloaca swabs. By contrast, rAAv10-nonUTR vaccination offered 70% protection, with 50% of chickens shedding the virus in the cloaca or throat swabs after the challenge. We conclude that the AAvV-10 UTRs can enhance the expression of the exogenous HA gene, resulting in improved efficacy of the rAAvV-10/HA vector vaccine. This improvement aids in the protection of flocks worldwide from the highly pathogenic avian influenza.

Managing the challenges of a highly pathogenic avian influenza H5N8 outbreak in Uganda: a case study

In 2016-2017, the H5N8 strain of highly pathogenic avian influenza (HPAI) spread worldwide and Uganda reported the first occurrence of the disease in its poultry and wild birds. Genetic analysis revealed that the virus clusters with 2.3.4.4 group B strains from birds in central and southern Asia, and thus forms part of the 2.3.4.4 group B clade. Since Uganda is in the path of two major migratory bird flyways, it is likely that infected migratory wild birds played a crucial role in the introduction of H5N8 HPAI viruses into Uganda. The outbreaks happened in the districts of Wakiso, Masaka and Kalangala and affected domestic and wild birds. A One Health Multisectoral Coordination Committee, consisting of a National Task Force, Technical Working Groups and District Disaster Management Committees, was immediately activated to coordinate the preparedness and response efforts to control the disease. In all the affected districts, surveillance was intensified on both domestic and wild birds; biosecurity measures were increased; and movement controls, culling, cleaning, disinfection and safe disposal of carcasses were implemented. Awareness of the disease was raised through education materials, leaflets and brochures distributed to farmers. Finally, Uganda successfully controlled the H5N8 outbreak, using its national preparedness and response mechanisms and through collaboration with international partners. The emergence and spread of this virus strain in Uganda and other parts of Africa poses a significant threat to the poultry industry and food security.

Pathogenicity and genetic characterisation of a novel reassortant, highly pathogenic avian influenza (HPAI) H5N6 virus isolated in Korea, 2017

We investigated influenza A(H5N6) viruses from migratory birds in Chungnam and Gyeonggi Provinces, South Korea following a reported die-off of poultry in nearby provinces in November 2017. Genetic analysis and virulence studies in chickens and ducks identified our isolate from December 2017 as a novel highly pathogenic avian influenza virus. It resulted from reassortment between the highly virulent H5N8 strain from Korea with the N6 gene from a low-pathogenic H3N6 virus from the Netherlands.

Genetic characterisation of novel, highly pathogenic avian influenza (HPAI) H5N6 viruses isolated in birds, South Korea, November 2016

A novel genotype of H5N6 influenza viruses was isolated from migratory birds in South Korea during November 2016. Domestic outbreaks of this virus were associated with die-offs of wild birds near reported poultry cases in Chungbuk province, central South Korea. Genetic analysis and animal studies demonstrated that the Korean H5N6 viruses are highly pathogenic avian influenza (HPAI) viruses and that these viruses are novel reassortants of at least three different subtypes (H5N6, H4N2 and H1N1).