Avian influenza is now circulating in dairy cattle in the United States, and has also spread to farm workers. How concerned should the UK industry be?
BODY COPY: With the worrying news coming out of the United States that avian influenza has been detected in cattle, it’s important for the UK poultry industry to keep ahead of the latest developments while the disease lays low during the summer months.
The UK Health Security Agency (UKHSA) has published a report, ‘Avian Influenza in Livestock’, summarising the risks within the UK, and making recommendations for animal health and veterinary professionals to continue monitoring developments in the USA and look for signs of zoonotic transmission in the animals they work with.
While the UK enjoyed a quiet AI season during the winter of 2023/24, the same cannot be said in other parts of the world.
Cattle
The first case of highly pathogenic avian influenza H5N1 in dairy cattle in the USA was recorded in December in Texas. The USDA published a report in June setting out how the virus had now been confirmed in 96 herd in 12 states, spread across the country by infected cows and machinery.
In addition, three workers on dairy farms have contracted mild cases of AI from infected cows. The virus has also killed nearly 97 million poultry in commercial flocks in the US over the past two years.
According to the UKHSA report, it is unknown exactly how or when the virus was introduced to dairy farms or how long the virus has been circulating undetected. ‘There are several possible routes of introduction including contact with wild bird cases, infected mammals or from undetected infected poultry,’ the report states. However, encouragingly for the UK, the genotype detected in cattle has only been found in the USA.
No mortality
In the affected dairy herds, the cattle are reported to have recovered within approximately two weeks of clinical onset. The associated human cases presented with conjunctivitis, which was the sole symptom and were treated with anti-viral agents. The World Health Organisation has said these cases appear to be the first occurrence of mammal-to-human transmission of avian flu.
European strategy
The European Commission, evidently concerned about the possibility of a pandemic, announced last month it had taken the extraordinary step of securing access to 40 million doses of avian flu vaccine for use in people.
The deal was announced by vaccine manufacturer CSL Seqirus, which was selected by the Health Emergency Preparedness and Response Authority (HERA), part of the European Commission (EC), to provide the vaccines. Under the terms of the agreement, CSL Seqirus will deliver 665,000 doses of pre-pandemic vaccine that is well-matched to the H5 of the currently circulating H5N1 strain, to 15 EU and EEA Member States. In addition, the four-year contract includes an option for participating authorities to purchase up to an additional 40 million doses of the pre-pandemic vaccine over the life of the contract.
This acquisition of pre-pandemic (zoonotic) vaccine will create a stockpile of vaccines available to support the EC’s outbreak and pre-pandemic response, the company said.
“While the ECDC assesses the risk of infection from avian influenza to be low for the general population, it considers people with activities that expose them to infected animals or a contaminated environment at low-medium risk,” said Raja Rajaram, CSL Seqirus, head of global medical strategy. “This agreement will help in Europe’s resolve to maintain robust preparedness and rapid response capabilities for this potential threat.”
The vaccines are being manufactured in CSL Seqirus’ European manufacturing sites in Amsterdam (for test and release) and Liverpool which utilises a scalable method of production and is one of the largest sites in Europe to manufacture seasonal influenza vaccines.
Avian influenza viruses do not normally infect humans, however, in rare cases humans have been infected with avian influenza viruses. Illness in humans from avian influenza has varied in levels of severity, from no symptoms or mild illness to severe disease and death. The spread of avian influenza from one human to another is very rare and typically has only spread to a few people.
Vaccine developments
Developments are also afoot in another part of the prevention strategy against avian influenza.
The two bird flu vaccines currently being tested in a field study have been found to protect laying hens from the disease eight weeks after vaccination. The study was carried out by Wageningen Bioveterinary Research (WBVR, part of Wageningen University & Research).
In the field study, which started in September 2023, 1,800 laying hens were vaccinated and housed on two commercial poultry farms. The trial at these two farms will run until the third quarter of 2025. On four occasions during this study, a number of the vaccinated chickens will be brought to WBVR. Here, the chickens will be infected with bird flu to study the effectiveness of the two applied test vaccines against the HPAI H5N1 virus. “We examine virus transmission – transmission – after vaccination, as well as survival rate, virus excretion and immune response. Based on these performances, we assess the effectiveness of the vaccines,” said Evelien Germeraad of WBVR. This first transmission study was conducted eight weeks after vaccination.
The field study is being conducted with two different vaccines: VECTROMUNE AI from CEVA Animale and VAXXITEK HVT-IBD-H5 from Boehringer Ingelheim. None of the vaccinated chickens became infected after contact with the avian influenza virus.
The transmission trial will be repeated three more times during the ongoing field trial.