In the melting of icebergs, icebergs could potentially contain long-dormant bacteria and viruses. Those viruses trapped in ice and permafrost for centuries, can be reactivated. That means melting those ice could potentially open a Pandora's box of diseases. Including some that have caused global epidemics in the distant past.
Example: babesiosis
As of regular ice. The freezing of bacteria in water isn't just an old practice and ice from unclean sources could also contain disease, when melted and ingested or touched this ice as well could transmit disease not so long-dormant, however still unpleasant.
