Highly pathogenic avian influenza A(H5N1) virus infections on fur farms connected to mass mortalities of black-headed gulls, Finland, July to October 2023.

Highly pathogenic avian influenza (HPAI) has caused widespread mortality in both wild and domestic birds in Europe 2020-2023. In July 2023, HPAI A(H5N1) was detected on 27 fur farms in Finland. In total, infections in silver and blue foxes, American minks and raccoon dogs were confirmed by RT-PCR. The pathological findings in the animals include widespread inflammatory lesions in the lungs, brain and liver, indicating efficient systemic dissemination of the virus. Phylogenetic analysis of Finnish A(H5N1) strains from fur animals and wild birds has identified three clusters (Finland I-III), and molecular analyses revealed emergence of mutations known to facilitate viral adaptation to mammals in the PB2 and NA proteins. Findings of avian influenza in fur animals were spatially and temporally connected with mass mortalities in wild birds. The mechanisms of virus transmission within and between farms have not been conclusively identified, but several different routes relating to limited biosecurity on the farms are implicated. The outbreak was managed in close collaboration between animal and human health authorities to mitigate and monitor the impact for both animal and human health.

Highly pathogenic avian influenza A(H5N1) virus infection on multiple fur farms in the South and Central Ostrobothnia regions of Finland, July 2023.

Since mid-July 2023, an outbreak caused by highly pathogenic avian influenza A(H5N1) virus clade 2.3.4.4b genotype BB is ongoing among farmed animals in South and Central Ostrobothnia, Finland. Infections in foxes, American minks and raccoon dogs have been confirmed on 20 farms. Genetic analysis suggests introductions from wild birds scavenging for food in farm areas. Investigations point to direct transmission between animals. While no human infections have been detected, control measures are being implemented to limit spread and human exposure.

Questionnaire survey of detrimental fur animal epidemic necrotic pyoderma in Finland.

BACKGROUND: In 2007, a previously unrecorded disease, fur animal epidemic necrotic pyoderma (FENP), was detected in farmed mink (Neovision vision), foxes (Vulpes lagopus) and Finnraccoons (Nyctereutes procyonoides) in Finland. Symptoms included severe pyoderma with increased mortality, causing both animal welfare problems and economic losses. In 2011, an epidemiologic questionnaire was mailed to all members of the Finnish Fur Breeders' Association to assess the occurrence of FENP from 2009 through the first 6 months of 2011. The aim was to describe the geographical distribution and detailed clinical signs of FENP, as well as sources of infection and potential risk factors for the disease. RESULTS: A total of 239 farmers (25%) returned the questionnaire. Clinical signs of FENP were observed in 40% (95% CI 34-46%) of the study farms. In addition, the survey clarified the specific clinical signs for different animal species. The presence of disease was associated with the importation of mink, especially from Denmark (OR 9.3, 95% CI 2.6-33.0). The transmission route between Finnish farms was associated with fur animal purchases. Some risk factors such as the farm type were also indicated. As such, FENP was detected more commonly on farms with more than one species of fur animal in comparison to farms with, for example, only foxes (OR 4.6, 95% CI 2.4-8.6), and the incidence was higher on farms with over 750 breeder mink compared to smaller farms (OR 3.8, 95% CI 1.6-9.0). Contact between fur animals and birds and other wildlife increased the risk of FENP on farms. Responses also indicated that blocking the entry of wildlife to the animal premises protected against FENP. CONCLUSIONS: FENP was most likely introduced to Finland by imported mink and spread further within the country via domestically purchased fur animals. Some potential risk factors, such as the type and size of the farm and contact with wildlife, contributed to the spread of FENP. Escape-proof shelter buildings block the entry of wildlife, thus protecting fur animals against FENP.