Netherlands Must Take More Measures to Prevent Bird Flu in Pigs & Protect Public Health: Experts Advise Mandatory Monitoring and Separation of Poultry and Pig Farms

The Netherlands must do more to prevent and detect infection of pigs with bird flu. That advised a panel of experts (the Experts’ Council on Zoonoses) to the Minister of Agriculture last week. Such infections pose a risk to public health, the veterinarians, virologists and epidemiologists write in their advice, because bird flu is a zoonosis: a disease that can infect both animals and humans and can jump between the two. When bird flu viruses infect pigs, they can mix with swine and human flu viruses. This could lead to a variant that can make people sick, spread easily between people and thus cause another pandemic.

“That chance is very small, but not zero,” says professor Ron Fouchier, virologist at Erasmus MC in Rotterdam and a member of the Expert Council-Zoonoses. Therefore, according to the experts, pigs and poultry should not be kept on mixed farms and there should be mandatory monitoring of flu viruses in pigs – especially on high-risk farms.

Since 2020, a highly pathogenic – very sickening – bird flu variant has been circulating among wild birds, which once originated in Chinese poultry. Since then, this variant has regularly caused outbreaks in poultry farms and has spread almost all over the world, resulting in a lot of animal suffering and economic damage. In the Netherlands alone, more than 6.6 million birds have been culled since 2020.

These mammalian infections are of concern because the virus can adapt to its host through mixing and mutation

Ron Fouchier professor

But the damage is also enormous among wild birds. In 2020, barnacle geese were the main victims in the Netherlands; in the last two years also other species, including white-tailed eagles, black-headed gulls and sandwich terns. In addition, wild mammals worldwide are increasingly becoming infected with the virus. Recent Dutch research showed that one in five wild mammals brought in dead carried the virus, or had recently had it. “These mammalian infections are of concern because the virus can adapt to its host through mixing and mutation, potentially becoming dangerous to humans, perhaps even pandemic,” says Fouchier. This happened, for example, in 2009 with the swine flu, which originated in pigs. That pandemic was relatively mild, but the Spanish (1918), Asian (1956) and Hong Kong flu (1968), which also originated in pigs, each killed millions.

Large-scale clearances

In recent outbreaks of bird flu among minks in Spain and sea lions in Peru, there was possibly already virus transmission between mammals. One of the mutations necessary for easy transmission between humans has already been seen in a polecat in the Netherlands.

Pigs are susceptible to swine, human and bird flu viruses. The Dutch pig sector is therefore a mixing vessel to be reckoned with, according to the experts in their recent advice. And that is precisely why rules and measures must be put in place to limit the risks – including systematic, mandatory monitoring. “In the poultry sector, this is already in order,” says Fouchier. “That may sound strange, given the large-scale culling. But it is precisely because of this that outbreaks are nipped in the bud. There is very strict monitoring.”

The situation is different in the pig sector, because the ministry considers swine flu viruses to be less dangerous than bird flu. The Ministry of Agriculture, Nature and Food Quality therefore leaves the monitoring to the sector itself – and there is also no obligation to report flu on pig farms. This is not regulated in Europe either. “While in my opinion there are enough reasons to set up proper monitoring in Pigsty Europe. And also make a good plan for what should happen in the event of an outbreak of bird flu. There is no such plan in the pig sector. I find that very strange.”

Manon Houben of Royal GD, formerly the Animal Health Service, is also a member of the Zoonoses Expert Council. She endorses the recent advice to the ministry, but would like to nuance the situation in the pig sector. “It is certainly not the case that there is no monitoring there and that we therefore have no insight into anything,” she says. GD, she explains, is a government owned company responsible for monitoring animal health in the Netherlands. GD is paid by the government and animal husbandry, including pig farmers.

Fine-meshed network

“We have close cooperation in the Netherlands between GD, livestock farms and veterinarians,” says Houben. “It is a fine-meshed network that exchanges information quickly and easily. For example, we receive dead animals that veterinarians send in when they see something suspicious, and we perform an autopsy on them. And we run the Veekijker, a telephone helpline with which veterinarians and livestock farmers can call to request information or to discuss a result. We record every call and analyze the statistics. And finally, all veterinarians who work for pig farms are obliged to send us a monthly report about those farms. The latter is part of the mandatory IKB quality system, Integral Chain Monitoring.”

No pig farm therefore remains under the radar, Houben emphasizes, because every farm uses the services of a veterinarian. And no vet will not report a suspected case of illness, she knows. According to her, a system in which a central inspection service comes to take virological samples unannounced has no added value.

We do not yet know enough what would be a good monitoring system

Manon Houben Royal GD

Given the seriousness of the current avian flu epidemic, various parties, including RIVM and GD, have started small-scale, voluntary surveillance this year. This trial, funded by the Ministry of Health, Welfare and Sport, maps out which swine flu viruses are circulating in pigs. Veterinarians take random samples from pigs that sniffle or cough at farms owned by farmers who want to participate in this. “Not all pigs have a cold, and not all companies,” Houben explains. “And not with pigs that are not visibly ill. But we do think that we get a representative picture this way – and that we can quickly detect any avian flu viruses that are present.”

The first results are expected at the end of this year. The trial has been set up for one year, but Houben expects a follow-up. The Zoonoses expert council recommends using the results to set up a larger-scale detection of avian flu among pigs. But according to Houben, other steps are needed first. “We do not yet know enough what would be a good monitoring system,” she says. “What information is needed exactly, how many samples do you need to take, what question do you actually want to answer? You can only design a good system once you have a clear picture of that.”

And the system must be good, according to her, because the sector must also benefit from it. “The monitoring we already have is really good. The infrastructure is in place, the people are there, and we can scale up and down quickly.”

Vaccinate employees

Arjan Stegeman is professor of farm animal health at Utrecht University and vice-chairman of the Expert Council-Zoonoses. “I think mandatory monitoring is especially relevant for high-risk farms,” he emphasizes, “such as mixed farms, farms where the pigs run outside and farms close to wetlands. If you read the advice carefully, you will get it out.”

Like Manon Houben, he does not see much added value in mandatory monitoring at all companies. “I see more in other measures,” he says, “such as urgent advice to people who work in that sector to get vaccinated against seasonal flu.” This is to reduce the risk of human and swine flu viruses mixing with each other. The Health Council is now considering such a measure.

Ordinary respiratory problems in pigs are very common

Arjan Stegeman professor

But Stegeman is somewhat more critical of the current monitoring. “Striking things are indeed reported,” he says. “But normal respiratory problems in pigs are very common. Only a small minority ends up at GD.” In other words, a flu virus that causes few complaints can lie dormant among pigs for a long time without being picked up.

So why not monitor all companies on a random basis? “I don’t think that’s a good idea,” Stegeman replies, “as long as we don’t know how to interpret the results and how to act then. Moreover, this monitoring offers a false sense of security.”

Although there are 12 million pigs in the Netherlands, he explains, there are more than 2 billion living elsewhere. “The chance that a new pandemic virus will arise in pigs is many times greater outside our borders than at home. There, these problems are on the same scale, but biosecurity is generally a lot less well regulated.”

What can we do about that? “Ensuring better hygiene at companies where the virus is constantly circulating,” Stegeman replies. “And vaccinate pigs. We in the Netherlands cannot do that for other countries. But we can do research into the effect on the dynamics of infection. How do viruses spread, and how can we intervene? That knowledge is also a product that we can export. That seems like a sensible priority to me now.”