Following an outbreak of bird flu in US dairy cattle, researchers have made progress to understand the potential of the disease to cause infection on a wider scale,  and the chances of it spreading to humans. 

The viral avian influenza strain, H5N1, has previously caused significant flu outbreaks in birds, and emerged again in April. It has since been identified in at least 140 dairy farms across the US (particularly in the cows’ milk), as well as in four dairy workers. 

In a study led by the University of Wisconsin-Madison, milk from infected cows was dripped into the noses of mice and ferrets, which led to severe disease in the animals. 

The team saw that infection by the virus could occur by drinking milk and breathing it in through the air, and could also spread to non-respiratory tissues such as the eye and muscle. However, in ferrets, they found that airborne transmission, between infected and healthy animals, was low.

Nevertheless, they found that H5N1 could bind to molecules on host cells that recognise both avian and human influenza viruses, raising the possibility that H5N1 is adapting to human hosts and may be able to affect people. 

The results have prompted calls for the need for greater monitoring and surveillance in affected, or exposed populations, of both animals and humans to track future risk.