© by aha! Swiss Allergy Centre - Info on allergies - Pollen allergy in the winter - trees with ice dust

A study launched by Swiss doctor Markus Gassner attracts strong interest in the "New England Journal of Medicine". It demonstrates that the non-native Spaeth’s alder (Alnus spaethii) has been flowering as early as Christmas for the past three years, which is proven to cause immune reactions in children. The study was carried out in cooperation with MeteoSwiss (Regula Gehrig) and the Allergy Unit of the University Hospital of Zurich (Peter Schmid-Grendelmeier).

The study

Markus Gassner regarding the background and objectives of the study: "The study actually started in 1981 with a school pupil who wanted to become a baker. He suffered from hay fever. I advised him to choose a different career, but he had already arranged an apprenticeship contract. His mother asked how great the risk of baker’s asthma was. As no one knew the answer, I submitted an application for research funding to the Swiss National Science Foundation. This was granted for 3 years. The result was the longest, continuous sero-epidemiological, longitudinal study (involving serum analysis) in schoolchildren in Switzerland, which ran from 1983 to 2007 in Grabs.

In the last few years we re-investigated the immune reactions of the schoolchildren from 1986 together with those from 2006, using a modern technique. We noticed that the students react with greater frequency to a molecule of alder pollen (rAln g 1). In 2010 we tested subjects who had taken part in this study back in 1986 and were now 39-year-old adults. They also reacted more frequently to this alder allergen. But why alders of all things, which have been very widespread for millennia in the floodplain forests of the young Rhine?

The explanation

Fifteen years ago 96 alders were planted in Buchs, St. Gallen. People wanted native trees, but a particularly attractive variety. Hence Spaeth’s alder was chosen. This variety had first been described in 1908 by Carlier in an arboretum in Berlin. This hybrid was a cross between a Caucasian alder and a Japanese or Siberian alder. Thanks to its more attractive leaves, it was further cultivated as an ornamental tree, it grew very quickly and proved to be winter-resistant.

In Buchs people noticed that for the past three years this tree had been flowering about two months before the alders on the Rhine Dam, always between Christmas and New Year. Consequently, pollen measurements had to be brought forward. Last year, alder pollen was detected two months earlier than at other measuring sites and it is expected to happen again this year.

Why do these trees flower so early?

Our deciduous trees have adapted to the seasons. In autumn they shed their leaves. This means they are better able to over-winter and store nutrients. They need a cold stimulus to sense that winter has arrived (the chilling effect). A cold spell, usually in early December, will have this effect. Then they await spring-time. Thanks to its Siberian gene, Spaeth’s alder may be able to risk more frost after coming into bloom than apple trees can, for instance. Connections such as these between environmental factors and genetics (epigenetics) are still largely unexplained, not only in humans but also for trees. That explains why these observations are extremely exciting. For instance, does temperature or light influence the start of flowering of these urban alders? Or is it a consequence of climate warming?

What should now be done about these trees?

The town council of Buchs is certainly reacting well to the situation. "These trees are not simply going to be chopped down to leave behind a concrete desert. However, it is a very good idea not to plant any new trees of this species here or anywhere else and hence avoid releasing an unnecessary quantity of risky allergens onto the streets of our towns and cities."

A summary of the study findings was published in the edition of 23 January2012 of the "New England Journal of Medicine". It is accessible to the public free of charge in the Online-Edition.

The people

Markus Gassner M.D.

Doctor in independent practice in Grabs (St. Gallen) 

During his work with the school doctor service he observed that children from farmers’ families suffer much less from hay fever and other allergies. He analysed this observation by means of blood samples over a period of 20 years. His widely published findings provided the impetus for national and international research at universities, initiated new therapeutic approaches and marked the beginning of the “hygiene hypothesis”. In 2008 Markus Gassner was honoured with an aha!award for his outstanding work.

Professor Peter Schmid-Grendelmeier

Head of the Allergy Unit, University Hospital of Zurich (blood tests)

Dr. Regula Gehrig Bichsel

Biometeorologist at the Federal Office of Climatology and Meteorology MeteoSchweiz (pollen measurements)

Editors: aha! Swiss Allergy Centre in co-operation with the Scientific Advisory Board. For prevalence figures, see source references.

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