Bird Flu Outbreaks in the Netherlands: Recent Updates and Future Outlook

2024-02-09 06:01:46

In recent years, there have been regular major outbreaks of bird flu among wild birds in the Netherlands. For example, in 2016 there was a major outbreak among mainly Wigeons and Tufted Ducks, in June 2022 many Sandwich Terns were affected and in the spring of 2023 thousands of Black-headed Gulls were affected. Things have been relatively quiet since then, although reports of sick or dead birds continue to come in. There are also still reports on poultry farms, with the last outbreak occurring in Putten on December 1, 2023.

Remembers viruses

The bird flu infections of the past two years were caused by the highly pathogenic virus type H5N1. Several variants of this type of virus have currently been found in both wild and domestic birds. It is not yet known whether these new variants are less contagious to birds than previous variants, or whether there are other explanations for the fact that there now appears to be less virus circulating and that there have been relatively few outbreaks this past winter.

More immunity

The virus has now been present in wild bird populations for months and is still causing mortality, although fortunately less than last summer. Some birds have built up partial protection against the disease, which means they die less quickly, but also remain ill for longer. This means that diagnosing the virus has become more complicated. Testing birds for the bird flu virus is usually done by taking samples from the trachea and cloaca. A bird only excretes virus (on average) during the first seven days of infection. If a bird is sick for longer before dying, the tests may be negative, but the bird may still have bird flu. It is therefore possible that birds that show symptoms of bird flu, such as tilting their heads, walking in circles, being unable to fly, etc., test negative. Other diseases can also cause these symptoms. The Dutch Wildlife Health Center (DWHC) is working with other research institutions in the Netherlands on better testing methods for diagnosing bird flu in dead wild birds.

Situation in Europe

There are now fewer outbreaks in other countries in Europe than in the autumn of 2023, but outbreaks still occur. Occasional outbreaks occur in Germany, France, Denmark, Hungary, Belgium, Poland, Bulgaria, Sweden and the United Kingdom, among others. It is difficult to predict what will happen in the coming months. The virus can mutate again and it is also possible that migratory birds will bring other variants to the Netherlands in the spring. The virus has not gone away and is expected to remain in the Netherlands in the coming months. The online bird flu radar shows that the chance of the introduction of bird flu in our region remains as high (see figure below). This prediction is based on a statistical model that uses data on the numbers, distribution and migration movements of birds in Europe.

Keep reporting dead birds

As long as bird flu is still circulating in the Netherlands, it remains important to quickly report dead or sick birds. This can be done at the Sovon reporting points or the DWHC.

Text: Sovon Bird Research Netherlands and Dutch Wildlife Health Center (DWHC)
Image: Peter de Boer (lead photo: Seagulls on the breeding island of Stern have fallen victim to bird flu (June 2023)); Sovon Bird Research Netherlands; EFSA’s Bird Flu Radar at app.bto.org/hpai