Tech & Science
Bird Flu Found in Sheep Milk: First Evidence of Mammary Transmission
Canadian vets found H5N1 and H5N5 bird flu viruses can pass from infected sheep to lambs through milk.
Two highly pathogenic avian influenza strains, H5N1 and H5N5, can be transmitted from infected sheep to their offspring through milk, according to a new study published in *Science Advances*. Canadian veterinary researchers say this is the first evidence that the viruses can spread via mammary glands in sheep, raising new concerns for farm biosecurity and public health.
The research team, led by Johannes Berhane of Canada's National Centre for Foreign Animal Diseases, launched the investigation after a suspected H5N1 case was reported on a British farm. In controlled experiments, the scientists injected particles of both H5N1 and H5N5 into female sheep and monitored the infection's progression.
Viral Replication in Mammary Tissue
The results showed that both viruses actively replicate in the sheep's mammary glands and accumulate in milk. This allows the viruses to pass to lambs during nursing. The study also found that direct contact within the flock can spread the infection.
"These viruses are evolving rapidly and spilling over into new animal populations, posing a major threat to their survival and to public health," the researchers stated. "We found they can actively replicate in the mammary glands of sheep and transmit through milk to their young. This is critical for monitoring influenza spread and protecting livestock."
Infected animals showed clear symptoms, including mastitis (inflammation of the udder), elevated body temperature, and a strong immune response, indicating a direct impact on the animal's health.
Implications for Farm Surveillance
The study concludes that highly pathogenic avian influenza can spread among sheep flocks not only through respiratory droplets or direct contact, but also through milk. The researchers recommend that milk transmission be included in veterinary surveillance and farm safety protocols, alongside strengthened prevention measures to curb the spread of infection.
Over the past four years, scientists have documented the rapid spread of H5N1 and H5N5 among large numbers of wild animals and birds across Europe and the United States.
