Influenza virus can infect breast tissue and spread via breast milk, researchers have shown.
Influenza - or "the 'flu" infects millions of people worldwide causing fevers, coughing, a runny nose and, in some cases, a lethal chest infection.
But no one had expected the agent to infect breast tissue, least of all Alyson Kelvin, from Toronto's United Heath Network, who was infecting baby ferrets to understand why influenza infections are so severe in the youngest and oldest members of society.
"We would infect the infant ferrets in the nose," she explains, "and they would pass the infection to their mothers. But then we were surprised to find the virus in the mother's breast tissue and in the milk, as well as in her airways."
The team ruled out spread of the virus from the nose and lungs via the blood to the breast.
"We think that the infection is spreading from the infant when it suckles."
Kelvin and her team suspect that virus shedding in the saliva of the suckling ferret is drawn into the nipple and inside the mother's milk ducts where it sets up an infection inside the breast, leading to short-term shedding of virus into future milk meals.
"But we think there may be a positive side to this," she says. "The virus infection in the breast might influence the immune system, leading to the production of protective antibody in future. It might also be a way to reinforce the infant's immune response by introducing the virus via the intestine."
However, there could also be a downside, because the infection can do damage locally, including causing blocked milk ducts and mastitis, and it could even carry a long term cancer risk as well providing a means to pass on the infection to uninfected pups.
The phenomenon, published this week in the journal PLoS Pathogens, may also not be restricted to 'flu.
"The same chemical present on our cells - sialic acid - that 'flu uses to infect us is also exploited by a range of other viruses, including agents that cause intestinal infections and respiratory illnesses, so this may be a generalisable immune mechanism."