Breastfeeding protects infants against human viruses even when mixed with formula

Most of the first wave of viruses turned out to be predators that grow in the first bacteria that colonize the infant gut. Later, at four months, viruses that can replicate in human cells and potentially make humans sick were more prominent in the babies' stools.

A strong protective effect was seen for breastfeeding, which suppressed the accumulation of these potentially pathogenic viruses. Similar results were seen for infants from the US and Botswana.

"These findings can help us better understand why some babies get sick and develop life-threatening infections in their first months of life," said senior author Frederic Bushman, Ph.D., chair of the Department of Microbiology.

The newborns' home country also played a part in the prevalence of viral infections. Babies from Botswana were more likely to have those potentially-harmful viruses in their stools at that 4-month mark compared to the stools of babies from the US.

"Location of the mom and baby seems to play a role, probably due to the kind and number of microorganisms babies are exposed to environmentally," said first author Guanxiang Liang, Ph.D., a postdoctoral researcher in the department at Microbiology. "Nevertheless, Botswana-born babies still seemed to benefit from breastfeeding, whether exclusively or in addition to formula consumption."

In the future, Bushman and Liang want to look at varying ages to see how the development of the virome -- the virus population in the gut -- influences a child's growth, how virome colonization varies in infants around the world, and how virome colonization influences outcomes in preterm birth.

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