Milk as a Transmission Vehicle for Highly Pathogenic Avian Influenza A (H5N1)

Highly pathogenic avian influenza A (H5N1) (H5N1 hereafter) is an emerging pathogen in mammals. The recent recognition of H5N1 in dairy cattle increases opportunities for human exposure and infection and may accelerate a trajectory toward sustained human-to-human transmission. Furthermore, the presence of virus at high concentration in unpasteurized milk raises new risks for humans, especially infants and children. Milk has been identified as a vehicle for viral transmission in and between mammalian species, including humans. Sialic acids (SAs) found on cell surfaces are important mediators of species susceptibility to specific influenza strains and play an important role in viral tropism. New data demonstrate that SA receptors with α2,3 linkages capable of binding avian influenza strains are present in human mammary tissue. The presence of SA receptors that can bind avian influenza and a comparative analysis of viral transmission risk of raw and pasteurized milk in several mammalian species have implications for human milk feeding. During this period of sporadic human infections with H5N1, further research and collaboration is warranted to address the potential risk of human milk contamination. Infants and children are particularly vulnerable to emerging infections during pandemics and have unique needs that may be overlooked. Pandemic preparedness must address the needs of all populations at all life stages, including pregnancy and infancy, and must include support for the safety of human milk.