Spain has ordered the confinement of all free-range poultry farms as of November 13 to curb the spread of H5N1 bird flu, following a rise in outbreaks across Europe and the southward migration of wild birds. The measure, while drastic, reflects growing concern about the virus's impact on both animal and human health.
H5N1 is a highly pathogenic influenza A virus first detected in domestic geese in China in 1997. Since then, it has spread globally via migratory birds, diversifying into genetic groups called clades. The current dominant clade, 2.3.4.4b, emerged in 2020 and has affected over 380 bird species, causing mass die-offs such as the loss of 40% of Peru's pelicans in under five months.
Since 2021, the virus has also infected more than 50 mammal species, including bears, sea lions, and domestic dogs and cats. In some cases, it has spread between mammals, such as elephant seals and fur farm animals. The virus causes symptoms ranging from pneumonia to neurological effects like tremors and convulsions.
In March 2024, the first H5N1 infection in dairy cows was reported in the United States, marking a significant shift. The virus was found to multiply in mammary tissue and shed in milk, with genetic mutations that enhance its ability to bind to mammalian cell receptors, raising concerns about zoonotic transmission to humans.
Despite these developments, the risk of a human pandemic remains low for now. The virus has not yet shown efficient human-to-human transmission, but health authorities are monitoring the situation closely as cases continue to rise in Europe and the Americas.
