Bird Flu & Livestock: Mammary Glands & Host Capacity
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H5N1 Avian Flu: Mammalian Susceptibility Broadens to Pigs, Sheep, and Humans
What happened?
A new study reveals that the mammary glands of pigs, sheep, goats, beef cattle, alpacas, and humans possess the biological characteristics necessary for infection by H5N1 avian influenza. This finding expands the understanding of potential transmission routes for the virus, which has primarily affected poultry and, more recently, dairy cattle.
As 2022, a highly pathogenic avian influenza outbreak has resulted in the culling of over 184 million domestic poultry. In spring 2024, the virus jumped to dairy cattle, infecting more than 1,000 herds as of late May 2024.
Key Findings & Scientific Basis
The research,led by Rahul Nelli of Iowa State University, focuses on the role of sialic acid. Sialic acid is a sugar molecule present on the surface of animal cells, acting as a crucial “docking station” for influenza viruses. It allows the virus to attach to and invade host cells.
Previous research by the same team demonstrated high levels of sialic acid in the udders of dairy cattle, explaining their susceptibility to H5N1. This new study extends those findings to other mammals, indicating a broader potential for transmission. Specifically, the study examined the receptor binding preference of H5N1 viruses to sialic acid found in the mammary glands of various species.
The study’s lead author, Rahul Nelli, a research assistant professor of veterinary diagnostic and production animal medicine at iowa State University, stated, “The main thing we wanted to understand in this study is whether there is potential for transmission among these other domestic mammals and humans, and it looks like there is.”
Species susceptibility: A comparative Look
| Species | Mammary Gland Sialic acid Profile | H5N1 Receptor binding Affinity (Relative) | Observed Infection (as of June 2024) |
|---|---|---|---|
| Poultry (Chickens, Turkeys) | High α2,3-linked sialic acid | Very High | Widespread |
| Dairy Cattle | High α2,3-linked sialic acid | High | Confirmed outbreaks in multiple states |
| Pigs | Mix of α2,3- and α2,6-linked sialic acid | Moderate-High | No confirmed outbreaks, but potential for amplification |
| Sheep/Goats | Mix of α2,3- and α2,6-linked sialic acid | Moderate | No confirmed outbreaks, but potential for amplification |
| Beef Cattle | similar to Dairy Cattle | High | Limited reports, monitoring ongoing |
| Alpacas | Mix of α2,3- and α2,6-linked sialic acid | Moderate | No confirmed outbreaks, but potential for amplification |
| Humans | Predominantly α2,6-linked sialic acid | Moderate | Limited human cases, primarily linked to poultry exposure |
Sialic acid profiles and H5N1 receptor binding affinity across different species