Avian Influenza update from December 2024 to March 2025 (EFSA)
Avian influenza alert: an evolving landscape for the European poultry sector
The European poultry sector is experiencing a period of heightened vigilance due to a marked increase in detections of the highly pathogenic avian influenza (HPAI) A(H5) virus, according to the recently published report “Avian influenza overview December 2024–March 2025” (73 pages) published by EFSA on 15 April 2025, covering the period from 7 December 2024 to 7 March 2025. This increase in detections, particularly of the A(H5N1) strain, already exceeds the total for the previous epidemiological year (2023–2024), although it remains below the levels recorded in the most critical preceding years.
Bird detections in Europe: persistence of the virus
During the period under review, 743 HPAI A(H5) detections were recorded across 31 European countries, affecting 239 domestic birds (poultry and captive birds) and 504 wild birds. The HPAI A(H5N1) strain was predominant, concentrated mainly in central, western and south-eastern Europe.
- Poultry: 167 HPAI outbreaks in poultry were reported across 16 countries. Italy, Poland and the United Kingdom (excluding Northern Ireland) accounted for 62% of these outbreaks and 81% of the birds culled, totalling nearly 10 million birds dead or depopulated. The vast majority (96%) of these outbreaks were caused by the HPAI A(H5N1) virus.
- Risk factors: Outdoor access for poultry remains an important risk factor at the wild–domestic bird interface. Indirect contact with wild birds was the most likely source of introduction in 80% of primary outbreaks investigated. Secondary spread between farms was also observed, particularly in Hungary, France, Albania, Belgium, Germany, Poland and Portugal. Genetic information suggests that some outbreaks reported as primary may in fact be secondary, as epidemiological investigations frequently fail to determine the exact route of virus transmission.
- Mortality: In commercial outbreaks, mortality in gallinaceous poultry ranged from 0.01% to 24.7%, while in ducks and geese it ranged from 0.6% to 75.5%. Mortality exceeding 5% may indicate delayed detection, prolonging the high-risk period and increasing transmission to other holdings.
- Wild birds: HPAI detections in wild birds increased by 17% compared to the previous period, with a total of 504 detections. Waterbirds such as mute swans, barnacle geese and greylag geese were the most affected, although a significant increase in the number of infected raptors was also observed. The Netherlands, Germany and the United Kingdom (excluding Northern Ireland) reported the highest number of detections. Detections of HPAI A(H5N5) declined, being more common in Iceland.
- Captive birds: 72 HPAI outbreaks were reported in captive birds across 14 countries. Several zoos were affected, particularly in Germany. This has reignited discussion on large-scale vaccination of zoo birds within the EU, as vaccination has proven effective in inducing seroconversion in these birds, especially Anseriformes.
Global detections and viral evolution: the threat spreads
Outside Europe, the total number of HPAI detections in domestic and wild birds officially reported to the World Organisation for Animal Health (WOAH) increased from 357 to 540.
- Americas: The USA and Canada accounted for 70% of outbreaks reported in domestic birds outside Europe. In the USA, the A(H5N1) epidemic in poultry remained at a high level, with confirmed infections in 63 commercial establishments and 69 backyard flocks, affecting 12.89 million birds.
- Antarctica: HPAI A(H5N1) was confirmed in Adélie penguins, petrels and skuas, suggesting an expansion of the host range and geographic range of the virus in the Antarctic and sub-Antarctic region.
Implications for animal and human health: mutations and exposure
Circulation of the virus in mammals is a growing concern.
- Non-human mammals: Detections of HPAI A(H5N1) and A(H5N5) in mammals in Europe were reported again from October 2024 onwards, following a period of absence.
- Domestic cats and wild carnivores: Several domestic cats tested positive in Italy, Belgium and Iceland, with infection suspected through contact with affected poultry or wild birds. The virus was also detected in red foxes in several European countries, as well as in an American mink, a Eurasian lynx and grey seals.
- Dairy cattle in the USA: The number of dairy cattle farms affected by HPAI A(H5N1) in the USA has risen to nearly 1,000 across 17 states. A different genotype (D1.1) was detected in this species, indicating at least two transmission events from wild birds to dairy cattle.
- Mutations: More than 50% of viruses characterised in mammals in Europe carry the PB2-E627K/V mutation, associated with more efficient replication in mammals. The increasing frequency of these mutations in birds (from 2.5% to 5.6% over the last epidemiological year) is a cause for concern, as it indicates that viruses with greater capacity to infect mammals can replicate and spread in birds.
- Human infections: Between 12 December 2024 and 7 March 2025, 22 new cases of avian influenza virus infection in humans were reported worldwide, including 12 A(H5) cases in the USA, two in Cambodia and one in the United Kingdom.
- Exposure: The majority of human A(H5) cases (93%) reported exposure to poultry or dairy cattle prior to virus detection.
- Overall low risk: The widespread circulation of avian influenza viruses in animal populations means that human infections remain infrequent. No evidence of human-to-human transmission was documented during the reporting period. The risk of infection for the general public in the European Economic Area (EU/EEA) remains low, but low to moderate for those occupationally exposed to infected animals or contaminated environments.
- Symptoms: The majority of human A(H5N1) cases in the USA presented with mild symptoms such as conjunctivitis or mild respiratory illness. However, severe cases requiring hospitalisation were recorded, along with three deaths (one in the USA, two in Cambodia).
Key recommendations for the poultry industry and veterinarians
In view of this situation, the need for medium- and long-term strategies is emphasised:
- Enhanced biosecurity:
- Farm siting: Avoid locating poultry holdings near wetlands or areas with high wild bird density.
- Biosecurity standards: Maintain and improve high biosecurity standards and their compliance, particularly on farms with outdoor access.
- Housing orders: Implement poultry housing orders (quarantine) during high-risk periods to reduce exposure to wild birds.
- Prevention of between-farm transmission: On holdings under the same ownership, shared personnel and equipment represent a risk. Strict biosecurity procedures are required for movement between establishments.
- Vaccination:
- Preventive vaccination is considered a valuable tool, particularly for zoo birds. Although real-world effectiveness data are limited, vaccination may serve as a complementary measure.
- Preventive vaccination is considered a valuable tool, particularly for zoo birds. Although real-world effectiveness data are limited, vaccination may serve as a complementary measure.
- Monitoring and surveillance:
- Surveillance in mammals: Increase virological and serological surveillance in free-ranging wild and domestic carnivores (cats, dogs) in areas with high virus circulation.
- Testing in ruminants: Consider testing in ruminants when unusual clinical signs are present (severe drop in milk production, thick and discoloured milk) or when HPAI infections have been identified in nearby animals.
- Genomics: Timely generation and sharing of genetic sequence data are crucial for the rapid detection of mutations that could increase zoonotic potential, antiviral resistance or alter antigenic properties. Genetic characterisation of avian viruses is recommended in areas where infections in mammals have been identified.
- Feed management:
- Safe feeding: Do not feed pets or other captive mammals raw meat, raw pet food or raw dairy products that have not been adequately tested for possible HPAI contamination.
The report underlines that the current epidemiological situation is fundamentally different from that prior to 2020, as HPAI A(H5Nx) viruses now persist year-round in European wild birds, rather than occurring only as seasonal epidemics. This persistence increases the risk of exposure for mammals and humans, requiring a coordinated One Health response between animal health and public health authorities.
For further information:
-. Avian Influenza update from December 2024 to March 2025. News item on NeXusAvicultura.com
-. EFSA Report: Avian influenza overview December 2024–March 2025. Published 15 April 2025 (73 pages)
-. Avian Influenza update September to December 2024. News item on NeXusAvicultura.com
-. EFSA Report: Avian influenza overview September–December 2024. Published 10 January 2025 (64 pages)
-. Avian Influenza update June to September 2024. News item on NeXusAvicultura.com
-. EFSA Report: Avian influenza overview report June–September 2024. Published 2 October 2024 (66 pages)
-. Avian Influenza on NeXusAvicultura.com