Published on 2 July 2026

Blog Corinne Gerber – Migratory birds and viruses

“My doctoral thesis highlights the role of migratory birds as potential vectors for the gradual introduction of viruses into Switzerland.”

Migratory birds as mobile reservoirs for insect- and tick-borne viruses: Findings from Switzerland

Each year over two billion birds are estimated to migrate between Europe and Africa. But this prodigious mobility poses substantial epidemiological risks. Migratory birds act as “biological shuttles” for the transport of pathogenic microorganisms such as viruses, bacteria or ectoparasites across national borders and continents.

A well-known example is the West Nile virus (WNV), an orthoflavivirus (formerly known as the genus Flavivirus) that normally circulates in a transmission cycle between mosquitoes (particularly the genus Culex) and birds. However, the virus can also occasionally be transmitted to humans and horses. In 2022, WNV was detected for the first time in mosquito populations in the canton of Ticino, specifically in the nature reserve Bolle di Magadino, an internationally important wetland where millions of migratory birds from a wide variety of origins converge in a confined space. This marked the starting point for a comprehensive investigation of the Swiss wild bird population in Ticino.

Interview with Corinne Gerber

• What was the aim of your doctoral thesis?

  When the West Nile virus was first detected in Ticino mosquitoes in 2022, it was not clear whether native wild birds were already infected as natural hosts without displaying any symptoms. To fill this knowledge gap, an active monitoring programme was set up in collaboration with the Institute of Microbiology at the University of Applied Sciences and Arts of Southern Switzerland in Bellinzona (SUPSI). We employed a multilayered approach combining specific molecular methods such as RT-qPCR (reverse transcriptase quantitative polymerase chain reaction) with non-specific next-generation sequencing (NGS) in order to investigate oropharyngeal-cloacal swabs collected from 496 wild birds (42 species in total) in the nature reserve Bolle di Magadino.

  NGS allows the entire genetic material contained in a sample to be collected without any preconceived assumptions. In this case, this includes all viruses of an organism (virome) without the prior specification of specific target viruses. Blood samples were also serologically tested for antibodies to orthoflaviviruses, including WNV. We then analysed ticks that we collected from the birds in order to identify potential vectors and their possible role in introducing viruses across ecological boundaries into Switzerland.

• What are the main findings of your thesis?

  A significant finding was the detection of orthoflavivirus antibodies in 15 out of a total of 164 blood samples. This proves that the investigated birds had survived an earlier infection with corresponding viruses. However, the available sample material was strictly limited (blood volume equivalent to max. 1 % of body weight) due to the small body sizes of the investigated bird species. Unfortunately, this meant that it was not possible to identify the specific orthoflavivirus with which the birds had previously been infected and distinguish between, for example, the West Nile virus (WNV), the Usutu virus (USUV) or the tick-borne encephalitis virus (TBEV). Further analyses allowed us to rule out an active viraemia caused by orthoflaviviruses at the time of sample collection. Nevertheless, the detection of antibodies in birds supports the hypothesis that migratory birds could act as potential vectors that gradually carry the viruses closer to Switzerland. This process might not necessarily involve direct migration from endemic areas, but rather via various stopover sites, thereby potentially promoting the establishment of new sources of transmission by infected mosquito populations. Finally, the virome data suggest that the composition of the avian virome is crucially affected by the food source and the local habitat at the sample collection site.

  A special highlight was the first detection of Bole tick virus 4 (BLTV4) in Switzerland.

  In a total of 22 analysed ticks, the virus was detected in four Rhipicephalus turanicus ticks. Although BLTV4 belongs to the family Flaviviridae, it is only distantly related to known human pathogens such as WNV or the TBE virus.

• To what extent will your findings help to advance research?

  The first Swiss detection of BLTV4 in ticks of the genus Rhipicephalus proves that migratory birds also act as mechanical vectors capable of transporting infected ectoparasites over large distances and ecological boundaries into Switzerland. These results illustrate the role of birds as intercontinental bridges for pathogens. In analysing the virome of songbirds (Passeriformes), my work addresses a gap in the global pathogen surveillance of birds, which has so far focused primarily on waterfowl (Anseriformes) and landfowl (Galliformes) or on investigations in the context of disease outbreaks.

• What aspect of this work are you particularly proud of?

  It was fascinating to experience how a basic idea ultimately turned into tangible scientific results. I'm particularly proud of being the first to detect BLTV4 in Switzerland. Since I had very little laboratory skills when I first started working at the IVI, I found it to be very instructive and exciting to experience for myself the steps from sample preparation through to the analysis of the NGS data.

• What did you especially like about working on your thesis?

  I especially appreciated the opportunity to make a concrete contribution to disease surveillance in Switzerland. Although I was unfortunately unable to take part in the sample collection in Ticino, I think it's great to see how people from differing locations can work together. At this point, I would like to express my sincere thanks to all those who made this project possible in the first place.

• How was your time at the IVI?

  Since my background is in veterinary medicine, my time at the IVI has given me an initial in-depth insight into the world of analytics, research and diagnosis. Although it has not always been easy, the mix of practical work in the laboratory, complex data analysis at the computer or the presentation of my results at professional conferences has made this an exciting and instructive period.

• What are your plans now, what's next for you?

  After submitting my thesis, I will continue working at the IVI for another three years. My next goal is to qualify as a veterinary specialist in laboratory and basic medicine (FVH). I will continue to specialise in my laboratory role and work in various disciplines at the sites in Mittelhäusern and Bern. So for me it's not a question of “goodbye”, but rather "here's to three more successful years"!