The U.S. Centers for Disease Control and Prevention reported that the avian influenza/bovine influenza H5N1 genotype B3.13 isolate obtained from a worker on a dairy farm in Texas in March was fatal to ferrets, a standard laboratory host for influenza viruses.  In contrast, human seasonal influenza produces characteristic clinical respiratory signs in ferrets but is not lethal.  It was however determined that the H5N1virus was less efficient at aerogenous spread than seasonal human influenza A strains but direct ferret-to-ferret transmission was confirmed. 

According to the CDC the finding in ferrets was not surprising but does not change the risk assessment that the virus is currently not generally infectious for humans.  A number  of mutations would be required for the virus to spread efficiently by droplets through the air.  This is the reason why virologists are analyzing the genomes of isolates derived from dairy cows, poultry flocks, marine and terrestrial animals, and the few human cases to date. It is important to detect changes that would predispose to a zoonotic strain in order to implement preventive modalities including PPE, biosecurity and vaccination.