Experimental study finds high H5N1 and H5N5 viral loads in milk of infected sheep

Sheep transmit high loads of H5N1 influenza virus through their milk and likewise transmit high loads of H5N5 influenza virus through their milk, according to a new study. The research, published in Science Advances, documented how lambs can spread infection to other udders by suckling.

@ScienceMagazine reported that the study documenting sheep transmission of H5N1 and H5N5 influenza viruses through milk and lamb suckling was published in Science Advances.

The findings establish that infected ewes can shed substantial quantities of both viruses in milk, creating a previously underappreciated transmission route. Lambs nursing from infected mothers can pick up the virus and then transmit it mechanically to other udders during suckling, the study found.

This cycle allows infection to move between teats on the same animal or potentially to other sheep in close contact.

The research focused on experimental infections that produced high viral loads in milk without necessarily causing severe illness in the ewes themselves. Scientists measured viral shedding over time and confirmed infectious virus in milk samples through laboratory culture.

Transmission via milk raises questions about risks in dairy sheep operations where milk is collected for human consumption or fed to other animals.

The study provides concrete data on viral stability and quantity in ovine milk, information that had been limited compared with cattle. Both H5N1 and H5N5 belong to the broader family of highly pathogenic avian influenza viruses that have circulated in wild birds and spilled over into mammals in recent years.

The sheep study adds to accumulating evidence that the virus can adapt to replicate efficiently in mammary tissue across multiple ruminant species.

Researchers emphasized the need for heightened biosecurity measures in sheep milking parlors, including pasteurization standards and separation of lambs from potentially exposed ewes. The work was conducted under high-containment laboratory conditions to prevent accidental release.