It has elements of ping pong but also of Russian roulette: the dynamics of bird flu. New variants of the virus are constantly emerging, which sometimes mainly affect poultry, sometimes mainly wild birds – but sometimes also claim human lives. In 2003 there was an outbreak in the Netherlands in which 30 million chickens were culled. 89 people also became infected with the virus; a vet died. Since 2014, there have been outbreaks with other variants. From October to July this year, all poultry in the Netherlands were forced to stay indoors, but a few companies were still infected.
Preventing an outbreak is better than a cure – but which is the smartest? There are all kinds of drawbacks to cages, says Janneke Schreuder, veterinarian and epidemiologist: “Both economically and in terms of animal welfare. You actually want to develop a much broader prevention approach.” Schreuder investigated the best way to do this. She obtained her PhD at Utrecht University on 13 July.
What about bird flu? Is it always so dangerous?
“New. There are many bird flu viruses, and many of them hardly make birds sick. We call these low-pathogenic. They originally circulate in wild bird populations. They are as mutable as human flu viruses – and they can spread to poultry. In intensive poultry farming, these viruses sometimes mutate into a highly pathogenic variant. This happened, for example, with the H7N7 variant in 2003 in the Netherlands.
“Since then, something different has happened in Asia: highly pathogenic variants of the H5 type have moved from poultry to migratory birds. It turned out that they did not always die immediately, so that those variants can maintain themselves in those populations. In the breeding areas, for example in Siberia, the Asian migratory birds come into contact with migratory birds from Europe. This allowed those variants to spread. So far, no humans have become ill, but it has already been shown that they can jump to seals and foxes.”
We can say that the highly pathogenic variants are now widely circulating in wild birds
How is the situation now?
“Now there are several highly pathogenic variants in circulation around the world. Which type is dominant and how sick birds get from it varies from year to year. This year, many wild geese fell ill in the Netherlands, but also scavengers such as birds of prey. Other years it is different species, such as wigeon or tufted ducks. We can say that the highly pathogenic variants are now widely circulating in wild birds and thus pose a risk to poultry and wild birds worldwide. That makes this topic increasingly urgent. Also because there is always the risk that a variant will arise that makes people sick.”
What exactly did you research?
“Among other things, whether you can tell from the poultry manure whether there is contact with wild birds. The hypothesis is that infections mainly occur through direct or indirect contact with feces of wild birds. The composition of the gut bacteria of chickens could be an indicator of that contact. We conducted an experiment in which we brought free-range and free-range chickens into contact with mallard duck manure and looked at the effect on the composition of their gut bacteria. The effects turned out to be very limited.”
I have created a model that allows you to predict where the risks of an outbreak are greatest
So that’s of no use to us?
“As an indicator for contact with wild birds, this is indeed not useful. But that knowledge is relevant. The gut microbiome is a hot topic. For example, other scientists are looking at how you can influence the health of chickens via the gut bacteria, for example by giving them probiotics. We now say: healthy laying hens have a stable microbiome that is not so easy to influence. In addition, we now know that it is better to focus elsewhere to predict the risk of bird flu outbreaks. For example, the presence of viral DNA in the water around a farm. And the distribution of wild birds in the area.”
You have researched that last factor yourself. How did that work?
“I used data from Sovon Ornithology Research for this. This organization collects very detailed data on the densities of bird species. I analyzed the distribution data of 54 wild species, mainly geese and ducks but also birds of prey, in combination with data from avian flu outbreaks between 2014 and 2018. Then I created a model that allows you to predict where the risks of an outbreak are greatest. We have made a risk map for the Netherlands based on that model. We also released the model on the latest outbreaks in 2020 and even those in 2021. Very exciting, because you can really see your model at work.”
And, what came out of that?
“That the model and the risk map provide a good indication of where the risk of outbreaks is greatest. But you do not yet know exactly how that transfer takes place. To be able to say something about causality, you would have to investigate the local conditions: the landscape, the actual presence of wild birds and whether they are infected, the movements of people and the role of, for example, mice, rats or other animals around the stables. ”
I find the interface between wild animals, domestic animals and human health intriguing
Does that mean we can benefit from your research?
“There is an expert group on animal diseases that advises the Ministry of LNV on measures. He is already using the risk map that has emerged from the model. In addition, my research has shown that mortality in laying hens is a very sensitive measure for early detection of bird flu infections, as well as mortality in combination with clinical signs in meat ducks. Thanks to this knowledge, companies and veterinarians can recognize bird flu more quickly.
“My research also shows how urgent the subject is, and how important it is that you keep a close eye on even the smallest changes in animal health on a farm. By the way, the Netherlands is leading the way in this regard; many other countries still have room for improvement. The covid pandemic has shown that you cannot be too careful with viruses that can transfer from animals to humans.”
Is that also a motivation in your work? Preventing pandemics?
“I don’t deal with that every day, no. I find my work particularly interesting because it is very diverse and very challenging. From field work at poultry farmers to die hard to model. I was initially trained as a horse doctor, but I find the interface between wild animals, domestic animals and human health, and where interests sometimes conflict, that is intriguing.”