Avian influenza in the USA: Danger for Switzerland too?
Since the end of March 2024, there have been more than170 confirmed cases of avian influenza (H5N1) in cows in the USA. We were interested in how experts assess the situation in Switzerland. PD Dr Christian Althaus from the Institute of Social and Preventive Medicine and the Head of the Institute of Virology and Immunology, Dr Barbara Wieland, PhD, answered our most pressing questions.
Text: Franziska Iff
How prepared are people in Switzerland for a pandemic caused by avian influenza?
The experience gained during the Covid pandemic has certainly sensitized the population to future pandemics. I therefore think that in the event of another serious pandemic, it would be easier to confidently implement measures with a low threshold such as wearing masks, working from home or limiting gatherings and events so that stricter measures such as shop or school closures would not be necessary.
Do we need to worry about our cats?
Cats can catch avian influenza by eating infected birds or drinking milk from infected cows. As there have been no confirmed cases of avian influenza in wild or farmed birds in Switzerland this year and there have been no cases in dairy cows, there is currently no risk to cats.
Are there any data/cases of human-to-human transmission?
There have been sporadic cases of human-to-human transmission of avian influenza over the last 20 years, but these have not yet been confirmed with absolute certainty.
How could the H5N1 enter Switzerland via animals?
The probability of the virus travelling from the USA to Switzerland is very low. Switzerland does not import live cattle from the USA. The only way would therefore be via wild birds, but then the virus would not yet be in the cows. Based on previous findings, however, new transmission events from birds to cows are still considered to be a very rare event. This requires a high viral load in the environment, such as in the case of a major outbreak in wild birds or farm poultry. Transmission from birds to cows could also occur through H5N1 influenza virus strains circulating in Europe. But this scenario is also unlikely now. In Switzerland, we have had no signs of virus circulation in poultry or wild birds for months and the influenza situation has calmed down across Europe in recent months.
Would we notice if H5N1 arrived in Switzerland?
The typical clinical symptoms in cows are massive mastitis with an acute drop in milk produciton. In an infected herd, several cows would quickly be affected, which rarely occurs with normal mastitis. Now that we have the raised awareness, we would quickly test for H5N1 in atypical cases of mastitis.
How is monitoring done?
The most efficient early detection is suspicion reporting by farmers and/or veterinarians. A high level of sensitization therefore makes sense there. In addition, Switzerland has a system based on bulk milk tank tests to ensure milk quality, which could detect cases with non-specific symptoms or subclinical mastitis. In special risk situations, this efficient system would provide easy access to bulk milk tank for risk-based testing for H5N1, for example. In addition, influenza is also covered by wastewater monitoring, which can be seen as a supplement to early detection.
How quickly could the chains of infection be broken?
With the systems we have in Switzerland and our experience with animal disease outbreaks, chains of infection could be broken more quickly in Switzerland than is possible in the USA. The animal movement database, in which all cows and their movements between farms are registered, plays an important role in the possibilities for monitoring. The conditions in Switzerland are not comparable with the situation in the USA.
Switzerland has a functioning reporting and testing system that, in the event of a currently unlikely outbreak of H5N1 in cows, provides data that enables an adequate response.