Which disease is least likely to be transmitted through banked breastmilk?

The least likely disease to be transmitted through banked breastmilk is syphilis. Syphilis is primarily a sexually transmitted bacterial infection caused by Treponema pallidum, and while it can have vertical transmission from an infected mother to her unborn child during pregnancy or childbirth, it is not effectively transmitted through breast milk.

In contrast, human immunodeficiency virus (HIV) can be transmitted through breast milk, and this risk has led to specific guidelines regarding breastfeeding in HIV-positive mothers. Hepatitis B virus (HBV) is also capable of transmission via breast milk, albeit the risk is comparatively low; however, it remains a concern when considering the safety of banked milk. Cytomegalovirus (CMV) is another virus that can be transmitted through breast milk, and it is particularly significant in premature infants or those with compromised immune systems.

Thus, syphilis stands out as the least likely disease to be transmitted through banked breastmilk, as it does not have the same transmission capabilities via lactation as the other listed pathogens.