#17,598
Yesterday the journal Eurosurveillance published a Rapid Communications from researchers from Finland's Institute for Health and Welfare (THL) and Food Safety Authority (Ruokavirasto) on the outbreak of H5N1 on 21 fur farms in central Finland we've been following for the past 3 weeks.
As we saw with the mink outbreak of H5N1 in Spain last fall (see Eurosurveillance: HPAI A(H5N1) Virus Infection in Farmed Minks, Spain, October 2022) there is some evidence of mammal-to-mammal transmission on these Finnish farms, and `. . . PB2 mutations associated with improved replication in mammalian cells have been detected in a subset of the fur animal cases'
This morning, Finland's THL published the following cautionary press release on this study (below, followed by excerpts from the study).
Avian influenza poses a risk to public health – improvements to health security needed at fur farms
4 Aug 2023
According to current data, avian influenza has spread to 21 fur farms in Finland. The first results from whole-genome sequencing indicate wild birds, particularly the black-headed gull, to be the source of infection.
This is reflected in the "rapid communication" article published in the Eurosurveillance journal by the Finnish Institute for Health and Welfare (THL) and the Finnish Food Authority. The article describes the avian influenza epidemic currently ongoing in fur farms in the Central and South Ostrobothnia regions of Finland.
“In the case of the more widespread infections at individual farms, the possibility of intra-farm infections cannot be ruled out. Current conditions on fur farms that do not have effective measures in place to protect the animals from birds enable the spread of viruses from wild birds to farmed animals. Risk management would require measures from fur farms to prevent birds from coming into contact with fur animals," says Terhi Laaksonen, Director of Department at Finnish Food Authority.
Based on genetic investigations, some of the viruses found in fur animals had mutations which indicate that the virus has adapted as a result of mammalian infections. Viruses bearing mutations that enhance the replication of the virus in mammalian cells were found on two farms.
It is important to monitor mutations related to pathogenicity, as avian influenza viruses mutate easily and mammalian adaptation could increase their pathogenicity in humans as well.
"The risk is particularly high with minks due to similarities between the respiratory tracts of minks and humans. Minks can also become infected with seasonal influenza by humans, which increases the risk of new viral variants to emerge", says Erika Lindh, Senior Specialist at THL.
"The matter has wider than only national significance. International health authorities and scientists also recognise the worst-case scenario of mammalian adaptation leading to a pandemic caused by an influenza virus that is new to humans," says Otto Helve, Director of Department at THL.
The publication describes the epidemic situation, the factors affecting its emergence, and infection management measures taken by the authorities.
Due to it length I've only posted some excerpts from the Eurosurveillance report (below). Follow the link to read it in its entirety. I'll have a bit more after the break.
Rapid communication
Highly pathogenic avian influenza A(H5N1) virus infection on multiple fur farms in the South and Central Ostrobothnia regions of Finland, July 2023
Erika Lindh1,* , Hanna Lounela2,* , Niina Ikonen1 , Tuija Kantala2 , Carita Savolainen-Kopra1 , Ari Kauppinen2 , Pamela Österlund1 , Lauri Kareinen2 , Anna Katz1 , Tiina Nokireki2 , Jari Jalava1 , Laura London2 , Marjaana Pitkäpaasi1 , Jaana Vuolle2 , Anna-Liisa Punto-Luoma1 , Riikka Kaarto3 , Liina Voutilainen1 , Riikka Holopainen2 , Laura Kalin-Mänttäri1 , Terhi Laaksonen2 , Hannu Kiviranta1 , Aino Pennanen1 , Otto Helve1 , Ilona Laamanen2 , Merit Melin1 , Niina Tammiranta2 , Ruska Rimhanen-Finne1 , Tuija Gadd2 , Mika Salminen1
Highly pathogenic avian influenza (HPAI) A(H5N1) virus belonging to clade 2.3.4.4b has since the end of April 2023 caused widespread outbreaks in wild and domestic birds in 25 countries in Europe [1]. In wild birds, black-headed gulls have been heavily affected, with mass deaths observed in many places, including in Finland. First reported on 14 July, an outbreak of avian influenza among farmed foxes, minks and raccoon dogs occurred in the regions of South and Central Ostrobothnia and is still ongoing. Up to 27 July, animals on 20 farms have been affected. Here, we provide an initial description of the outbreak and control measures taken, and discuss the source, potential reasons for and consequences of the outbreak.
Outbreak setting
Several types of animals are commercially farmed for fur production in Finland, including American mink (Neovison vison), arctic (blue) fox (Vulpes lagopus), red (silver) fox (V. vulpes) and their crossbreeds, raccoon dog (Nyctereutes procyonoides) and sable (Martes zibellina). There are over 500 farms in the country, and 95% of the fur production (1.3 million animals annually) is concentrated in western Finland. Animals are mostly kept in side-by-side wire-mesh cages in narrow raised sheds (shade houses). These are only covered by a roof and have no closed walls. Birds, including gulls and jackdaws, visit the farms and seek access to the feed of the fur animals in the shade houses. Outbreaks of HPAI subtype H5N1 among birds, especially black-headed gulls, with mass wild bird deaths have occurred in multiple regions of Finland during the summer of 2023, as in almost all European Union/European Economic Area countries [1].yet. Active control measures appear to be effective, while culling of the animals is underway. The ongoing epizootic of HPAI H5N1 among gulls and other birds poses a risk of re-introduction in the current farm settings. It is clear that current conditions on the majority of farms cannot prevent bird access and much more rigorous biosecurity measures would have to be put in place at the industry level to eliminate these risks.The sequence data indicate that, at least originally, transmission likely occurred from birds to the fur animals, most probably through contacts in the shade houses. Birds have easy access to the interior of the shade houses and gulls have frequently been observed in the vicinity of the farms. Mass deaths of gulls have also occurred in the same general region. Other potential exposure possibilities have been investigated, such as contamination of fur animal feed by birds or indirect spread by the workers while handling or feeding the fur animals. In addition, direct contacts between farms through personnel or animal movements, have been investigated and excluded as a cause of spread. In theory, an infected human could have transmitted the disease to the animals, but no evidence exists to support such a scenario.At present, it appears likely that transmission among fur animals is contributing to the evolution of the outbreak, and PB2 mutations associated with improved replication in mammalian cells have been detected in a subset of the fur animal cases. A well-recognised concern exists that prolonged replication of the HPAI H5N1 virus in a high-density mammalian population, such as the fur farms, might lead to viral forms that could more easily spread among humans [8-10]. As there is little prior experience of outbreaks similar to the one described here, it is not possible to predict the outcome. Thus, no firm conclusions can yet be drawn on the current risks for fur animal-to-human or human-to-human transmission.Outbreak description
On 12 July 2023, the Finnish Food Authority (FFA) informed the Finnish Institute for Health and Welfare (THL) about a suspicion of cases of avian influenza among farmed fur animals on five farms in the South and Central Ostrobothnia region of western Finland. Because of rising mortality on the farms, especially in juvenile fur animals, cadavers were sent to the FFA laboratory for analysis. Dead animals exhibited no obvious cause of disease but had lesions in the lungs and signs of septicaemia. Follow-up investigation by FFA revealed symptoms characteristic of HPAI H5N1 virus infection in mammalian species (lethargy, neurological signs, diarrhoea, rapid death) occurring among the fur animals on affected farms. Subsequently, the causative agent was confirmed by PCR at FFA to be HPAI H5N1 virus clade 2.3.4.4b. This is only the second known outbreak of infection by this avian influenza virus variant at fur animal farms in Europe, after one reported in 2022 in Spain [2].
To date, 27 July 2023, 20 affected farms in four municipalities of Central and South Ostrobothnia have been identified (Figure) with blue and silver foxes and their crossbreeds, raccoon dogs and minks being infected. The affected farms, which vary in size from 600–50,000 fur animals, house a total of 37,900 minks, 142,463 foxes and 5,400 raccoon dogs (a total of 185,763 fur animals, each farm rearing 1–3 species).
Origin of the infection on fur farms
Preliminary results from whole genome sequencing of 14 representative individual fur animal samples from 11 farms (fox n = 11, mink n = 3) and from seven wild black-headed gulls from mostly nearby municipalities in Finland (GISAID accession numbers are provided under Data availability) from the outbreak, confirm that all the HPAI samples from fur animals are BB genotype. BB genotype is a H5N1 virus variant widely found in seagulls all over Europe, and similar to HPAI H5N1 present locally in gulls (data not shown), suggesting that at least the original exposure and transmission stems from exposure to the birds [1]. Phylogenetic analyses further suggest that several introductions from birds to the fur animals may have taken place but are also consistent with possible transmission among the fur animals themselves and potentially even between species. Transmission between fur animals is also supported by the general epidemiological pattern of several hundreds of sick and dead animals on the 20 farms (mortality on affected farms has been 2–4 times the normal rate and, at the peak of the outbreak, a large farm recorded almost 400 deaths in one day, which is 10 times the normal rate). The exact mechanism of the transmission within and between farms is, however, not yet known.
Some evidence for adaptation to replication in mammals is evident, as the PB2 gene E627K change was detected in samples from one farm and the T271A change in a sample from another farm.
(SNIP)
Discussion
The HPAI H5N1 outbreak on fur farms in South and Central Ostrobothnia in Finland, which was detected in July 2023, is not over yet. Active control measures appear to be effective, while culling of the animals is underway. The ongoing epizootic of HPAI H5N1 among gulls and other birds poses a risk of re-introduction in the current farm settings. It is clear that current conditions on the majority of farms cannot prevent bird access and much more rigorous biosecurity measures would have to be put in place at the industry level to eliminate these risks.
The sequence data indicate that, at least originally, transmission likely occurred from birds to the fur animals, most probably through contacts in the shade houses. Birds have easy access to the interior of the shade houses and gulls have frequently been observed in the vicinity of the farms. Mass deaths of gulls have also occurred in the same general region. Other potential exposure possibilities have been investigated, such as contamination of fur animal feed by birds or indirect spread by the workers while handling or feeding the fur animals. In addition, direct contacts between farms through personnel or animal movements, have been investigated and excluded as a cause of spread. In theory, an infected human could have transmitted the disease to the animals, but no evidence exists to support such a scenario.
At present, it appears likely that transmission among fur animals is contributing to the evolution of the outbreak, and PB2 mutations associated with improved replication in mammalian cells have been detected in a subset of the fur animal cases. A well-recognised concern exists that prolonged replication of the HPAI H5N1 virus in a high-density mammalian population, such as the fur farms, might lead to viral forms that could more easily spread among humans [8-10]. As there is little prior experience of outbreaks similar to the one described here, it is not possible to predict the outcome. Thus, no firm conclusions can yet be drawn on the current risks for fur animal-to-human or human-to-human transmission.
Conclusion
No human infections have been detected thus far in the current fur farm outbreak in Finland and, globally, there is no verified transmission of HPAI H5N1 virus infection from another mammal to humans. However, this outbreak does raise concerns for the future, not only in Finland but in the global context. Thus, very rigorous monitoring of the situation at fur farms in Finland is being implemented in close cooperation among national authorities and in consultation with relevant international public health agencies. More detailed analyses of the outbreak are planned to be published as sequencing and potentially also serological data become available.
The concern, particularly with high density animal farms, is that it provides the virus with an ideal environment to spread from mammal to mammal. Long chains of infection (see graphic below) can provide the virus with additional opportunities to adapt to a new host species, furthering its evolution.
While fur farms aren't the only place where these conditions exist, mink (and to a lesser extent, foxes) are particularly susceptible to influenza A viruses (see PNAS: Mink Farming Poses Risks for Future Viral Pandemics), and they are usually raised in extremely close quarters facilitating transmission.
Last May, in Study: Seroconversion of a Swine Herd in a Free-Range Rural Multi-Species Farm against HPAI H5N1 2.3.4.4b Clade Virus we also looked at a similar spillover into pigs on a `mixed species farm' in Ostia, some 300 miles to the south of Brescia.
Pigs, fortunately, aren't nearly as susceptible to H5N1 as mink, although that could change over time (see Netherlands: Zoonoses Experts Council (DB-Z) Risk Assessment & Warning of Swine As `Mixing Vessels' For Avian Flu).
The quantity, diversity, and geographic range of HPAI H5 avian flu viruses in the wild has soared dramatically over the past couple of years, making common practices - like `mixed-species' farming - far more risky.
While it may be a bitter pill for many to swallow, we must either adapt to living and working in this new virus-laden environment, or risk that the virus will eventually adapt to us.
