Like some diseases
I believe the answer is:
viral
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">like some diseases</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for viral that I've seen before include "(Of video) fast spreading" , "Like many diseases" , "Of organisms causing 'flu, etc" , "Rapidly becoming popular online" , "Of organisms that transmit infectious disease" .)