The outbreak of H5N1 avian influenza in a Spanish mink farm is raising concerns about transmission to humans.

Raccoons, foxes and martens – bird flu viruses have already been found in these and other mammals. Humans have also been infected and have died from it. In these incidents, the viruses have usually passed from a bird to a mammal in isolated cases. But in the avian flu outbreak at a Spanish mink farm in October 2022, the H5N1 avian flu virus spread from mink to mink. A mutation was found in the sequenced viruses from this outbreak that could indicate adaptation of the bird-derived H5N1 to mink, but this interpretation of the findings is not yet certain. A research team has now found this out and published it. It is possible that this could make the virus more dangerous to humans. Professor Schulz answers some questions:

Professor Schulz – How great is the current risk for humans to contract an H5N1 infection and how great could it still become?

At present, the risk of transmission to humans, and in particular the risk of spread from person to person, is still considered very low. It appears that none of the employees of the Spanish mink farm were infected during this outbreak. However, the recent massive spread of the H5N1 virus among wild birds is a cause for concern.

What can be done at present to prevent transmission to other animals and humans?

It is essential to avoid contact with dead birds found, for example, during a walk on the beach. Furthermore, it is necessary to react immediately if an outbreak of H5N1 is found in poultry flocks – this is already happening. The aforementioned H5N1 outbreak in the Spanish mink farm shows that such factory farms pose a potential danger. During the COVID-19 pandemic, SARS-CoV-2 had also spread in several mink farms, new variants had emerged there, which were then transmitted to humans again. In some countries, the mass keeping of mink in such forms was therefore banned either temporarily or permanently.

Do we know why human-to-human transmission has not yet occurred?

The haemagglutinin protein of H5N1, which the virus uses to ‘dock’ with its cellular receptor, the carbohydrate structure neuraminic acid, is not yet optimally adapted to the form of neuraminic acid found in the upper human respiratory tract. The concern is that as the virus spreads into mammalian populations such as mink, the H5N1 haemagglutinin, or other viral proteins, could mutate in such a way that its replication in human cells is faster. This would theoretically allow the virus to spread faster from human to human. But so far this has not happened.

Could the bird flu virus cross with a human flu pathogen?

Yes, theoretically, there is a possibility that the avian influenza virus – if a mammal is infected with an H5N-1 fowl plague virus and a human influenza virus at the same time – could pick up elements of the genome of a human influenza virus and thus better infect human cells and spread among humans. But even this has not happened in the case of the H5N1 avian influenza virus so far.

Professor Schulz, thank you very much for this interview.