Thanks for your comment David.

Most of these large of giant viruses were (and are still) discovered in aquatic environment (fresh, brackish, or marine waters). They were ignored (missed) simply because since the very beginning, "viruses" were meant to be much smaller that other microbes (such as bacteria, eukaryotic plankton cells, etc). Thus the very first step of any analysis of the virus content in a sample started by .... filtering the water through a 0.2 micron porosity filter, thus the megaviruses were retained on the filter, with the bacteria and other cellular microbes.

The flurry of discoveries of giant viruses (the one that do not go through the filters) is thus simply due to the fact that scientists have changed their protocols following the serendipitous discovery of the first giant virus, Mimivirus, in 2003.

Thus these discoveries do not correspond to a new phenomenon (for instance related to global warming), and these viruses have been around for billions of years, notably in the oceans were they regulate the population of the microalgae responsible for the production of 1/3 of our oxygen.

Thus don't worry, this is not like a new epidemic. Moreover, for reasons that are not clear yet, giant viruses seems to restricted to unicellular microbes, and none of them infect multicellular organisms (including terrestrial plants, animal and humans). This is probably due to special evolutionary constraints that are not yet clear, but could be linked to the absence of immune defense mechanisms in these unicellular hosts.

So, in conclusion, don't worry: these giants viruses do not correspond to a new threat: not new, because they always have been here, and no threat because they only infect microbes. You can continue to take a swim!