A new study shows that the current H5N1 bird flu virus can infect mice and ferrets. This virus spreads through milk and breathing, making it a bigger pandemic risk than before. The H5N1 virus, originally from Asia, has been infecting birds for years, killing millions. Recently, it was found in dairy cows in the USA, which produced less milk due to the infection. The virus spread quickly among the cows, and some people, cats, and birds on farms also got infected.

Scientists are not sure how the virus jumped from birds to cows and then to other animals and humans. They think it might have spread through contaminated milking equipment or contact with infected milk glands. The virus was found in the cows' milk and noses. Pasteurized milk is safe, but the virus can spread through breathing too.

Researchers from the University of Wisconsin-Madison studied how the H5N1 virus behaves in other mammals. They used infected milk from a cow and older virus strains. They found that the virus spread to mice and ferrets through milk and breathing. Unlike cows, the mice and ferrets got sick or died. The virus spread throughout their bodies, including lungs and milk glands.

Mother mice passed the virus to their babies through milk, and the virus also spread through tiny droplets from breathing. However, this didn’t make the animals very sick, possibly because of the lower amount of virus in the droplets.

The study found that the virus is more likely to spread through milk. The researchers also tested if the virus could infect birds and humans again. They found that the virus can attach to receptors in the respiratory systems of both. This means the current H5N1 strain in cows is more contagious to mammals, including humans, than older strains.

While it is possible for humans to get H5N1 and become seriously ill, it has been rare so far. But the new strain could change that and increase the risk of human-to-human transmission. More studies are needed to understand how likely and quickly this could lead to a pandemic.