Tuesday, May 09, 2023

Netherlands: Zoonoses Experts Council (DB-Z) Risk Assessment & Warning of Swine As `Mixing Vessels' For Avian Flu



Yesterday (May 8th) the Ministers of Health (Adema) and Agriculture (Kuipers) for the Netherlands sent their House of Representatives a letter detailing advice from their Experts Council on Zoonoses (DB-Z) on the risks of avian flu influenza to public health.  

Although this letter covered a lot of territory, one of their biggest concerns centered around `mixed farming', where pigs and poultry are raised in close proximity providing opportunities for H5N1 to spillover into swine. 

This is obviously not a new concern as we've known that H5N1 can infect pigs for nearly two decades.  Between extremely limited testing, and the fact that H5N1 tends to be asymptomatic (or mildly symptomatic) in pigs, it is probably more common than we realize. A few reports include:

WHO H5N1 detected in pigs in China (2004)

EID Journal: Asymptomatic H5N1 In Pigs (2010)

An Unusual Report Of H5N1 in Pigs (Indonesia 2016) 

With the enormous surge of H5N1 around the world, two months ago the ECDC/EFSA Avian Influenza Overview December 2022 – March 2023 warned:

The additional reports of transmission events to and potentially between mammals, e.g. mink, sea lion, seals, foxes and other carnivores as well as seroepidemiological evidence of transmission to wild boar and domestic pigs, associated with evolutionary processes including mammalian adaptation are of concern and need to be closely followed up. 

The spillover of SARS-CoV-2 to farmed mink in Denmark in 2020 and the spill back into humans of a mutated variant (see Denmark Orders Culling Of All Mink Following Discovery Of Mutated Coronavirus), along with the recent discovery of a Cryptic SARS-CoV-2 Lineage on Two Mink Farms In Poland, are reminders how mutable novel viruses can be. 

Pigs aren't the only mixing vessel we worry about, of course. But Swine possess both avian-like (SAα2,3Gal) and human-like (SAα2,6Gal) receptor cells in their respiratory tract, making unusually well suited for the task.

Humans can act as mixing vessels as well (see The `Other Mixing Vessel' For Pandemic Influenza), making it important that those who work with wild birds, poultry, or swine get vaccinated against seasonal influenza each year. 

This risk is also addressed in the Netherlands report, along with news of the detection of evidence of H5N1 infection in stray cats.

I've translated excerpts from the 7-page report below.  I'll have a brief postscript after the break. 

Dear Chairman,

At our request, the Center for Infectious Disease Control (CIb) of the RIVM convened on 7 March 2018 the Expert Consultation on Zoonoses (DB-Z), consisting of human and veterinary infectious disease experts, to advise on the risks of avian influenza for public health. We received the final version of the advice and the list of those present on 3 April 2010 and can be found in the appendices to this letter. This is the second advice from the DB-Z on bird flu, the first advice was received by your House on 1 June 2022 (Parliamentary Paper 25295, no. 1872) .

In this letter we present the epidemiological situation and interpretation as outlined by the DB-Z. We then discuss the advice of the DB-Z and immediately provide a policy response.

Epidemiological situation

For the third consecutive season there has been increased circulation of Highly Pathogenic Avian Influenza (HPAI) H5N1 among wild birds in the Netherlands. There is increasing geographic distribution across the world, including in areas where no HPAI previously existed. HPAI H5N1 is regularly found in mammals in several parts of the world, now more than 30 species, with mutations that can be considered as adaptation to mammals being found more often. In a recent outbreak on a mink farm in Spain and an outbreak among sea lions off the coast of Peru, mammal-to-mammal transmission could not be ruled out. HPAI H5N1, belonging to the same clade as currently circulating in Europe, has also been demonstrated in a few people, with two people also showing symptoms.

The risk of spreading HPAI in the Netherlands has not changed. The DB-Z estimates that the risk for the general population remains low and for people with occupational contact with poultry/infected animals low to moderate. The DB-Z indicates that the increase in infections among wild mammals and the increased global distribution have increased uncertainty about the risk assessment. The regularly reported infections in mammals also require increased vigilance in the Netherlands, especially because the Netherlands has one of the highest densities of animals in the world.

Opinions and policy response

The DB-Z underlines the previous advice and adds a few. Below we discuss the new advice. In the letter, which was previously promised about the main points of the intensification plan, we inform you about the implementation of the previous DB-Z advice.


With regard to seasonal flu vaccination, the DB-Z indicates that people who are potentially exposed are now finding it difficult in practice to get vaccinated against influenza. Seasonal flu vaccination can reduce the risk of human seasonal flu strains mixing with bird flu strains, resulting in a dangerous variant of (avian) flu for humans. We want to further lower the threshold for getting a flu vaccination by facilitating the seasonal flu vaccination for people who may come into professional contact with avian influenza. This is well arranged for NVWA personnel who are involved in culling.

The next step for the seasonal flu vaccination this fall is to lower the threshold for people involved in cleaning up dead or sick wild birds and mammals and keepers of poultry or pigs. An analysis is being carried out of what can be done additionally in the purchase and distribution of vaccines. Because these risk groups can best be identified by employers, voluntary organizations and sector representatives, consultations will be held with these organizations about the method of providing the vaccination.

The DB-Z also considers it a risk that (volunteer) organizations, such as bird shelters or animal ambulances, have to pay for personal protective equipment themselves. The personal protective equipment that was in stock in the context of corona is now being phased out and has been made available to animal aid organizations and to other volunteers who come into contact with wild animals infected with bird flu. These are large quantities and will provide the organizations with this for years to come. It is important that people who may come into contact with infected animals protect themselves well: communication about this to the parties involved in the removal of dead wild animals that may be infected with bird flu is being intensified. 


Pig farming and bird flu

In its advice, the DB-Z indicates that pigs are a potential mixing vessel for HPAI and swine influenza viruses. The DB-Z advises developing surveillance at pig farms, as this system could focus on the farms with the greatest risk. The DB-Z refers to mixed poultry/pig farms, pig farms with free range or pig farms in areas rich in waterfowl. The DB-Z also advises that biosecurity (aimed at reducing the risk of introducing avian flu) should be given more priority on pig farms. According to the DB-Z, humane surveillance of pig farmers should also receive more attention. Pig farmers should be included in the aforementioned proactive monitoring if bird flu is detected on a pig farm. Finally, the DB-Z recommends a reporting obligation for HPAI in pigs and action options should be worked out if avian flu is detected on a pig farm.

The aforementioned advice from the DB-Z in the field of pig farming will be taken up by the Minister of Agriculture, Nature and Food Quality. Pigs are currently already sampled if there is an outbreak among poultry on mixed farms. HPAI virus has never been detected in pigs in the Netherlands. A pilot is currently running on influenza strains on pig farms, and we expect the results in the autumn. After the evaluation of these pilot results, the surveillance for influenza viruses on pig farms will be continued. RIVM recently submitted a project proposal to the European Commission for systematic surveillance of bird flu and swine influenza, with a focus on risk-based surveillance of wild mammals, pigs kept outside and the environment (water).

Wageningen Bioveterinary Research (WBVR) recently started a research project into research into influenza virus transmission in pigs, within and between pig farms. Based on this research, effective management strategies may be developed to reduce the risk of introduction and transmission of influenza strains. By means of these and the aforementioned studies, we hope to be able to provide pig farmers and veterinarians with sufficient insight and tools in the long term to prevent the introduction of influenza viruses on pig farms, or to minimize the consequences of an introduction. The results of the relevant studies are also used for a biosecurity plan for pig farming. The implementation of this was previously announced in the National action plan to strengthen such önosenpolicy .

RIVM is working on proactive monitoring for poultry farmers and others who may have been exposed to the bird flu virus. RIVM has been asked to include pig farmers in this monitoring. The Minister of Agriculture, Nature and Food Quality is exploring how a reporting obligation for highly pathogenic bird flu in pigs can be introduced. Consultation is also taking place with the parties involved. It is important that pig farmers and veterinarians know where they stand when such a report is made. That is why the different scenarios and associated consequences of an infection are discussed with the stakeholders involved. The Minister of Agriculture, Nature and Food Quality will inform the Lower House about the obligation to report bird flu in pigs in the context of the bird flu prevention intensification plan.


The DB-Z report states that a study by the Faculty of Veterinary Medicine among stray cats found evidence in the blood of some of the cats that they have ever been in contact with H5 influenza. The investigation is ongoing and the findings have yet to be confirmed. It remains to be seen how specific these results are to HPAI or whether cross-reactivity with other types of influenza may have occurred. 

It has been known for some time that cats and dogs can be susceptible to bird flu: in America and Canada, infections have been found in dogs and so-called 'barn cats' (semi-feral cats). It is therefore good to reiterate the advice to avoid contact between dogs or cats with dead or sick birds and to consult the vet if it is suspected that an animal has become ill after contact with a dead or sick bird

(Continue . . . ) 

As welcome as their proactive stance against avian flu is, it also reminds us that in much of the world, little or nothing is being done to mitigate the risks.  Testing - of pigs, poultry, or humans - is severely limited, `mixed farming' is a common practice, and some countries seem more interested in hiding outbreaks than preventing them. 

Although we've been watching the evolution of H5N1 - mostly in birds - for more than two decades, the virus has dramatically expanded its host range (both in birds and mammals), and its genetic diversity (number of genotypes), over the past couple of years.  

While there still may be some undefined species barrier that prevents H5 from sparking a human pandemic, this recent expansion provides the virus with a lot more opportunities to win the pandemic lottery. 

Of course, Avian H5N1 is just one of the contenders.  There are other credible threats (e.g. MERS-CoV, H5N6, H3N8, Nipah, etc.) which get far less attention, and could prove equally dangerous. 

Which is why the next pandemic isn't a matter of `if', its only a matter of `when'.