I love this line of thinking but the framing comes across to me as a bit inflammatory and uncharitable. Just about anything involved in the exchanged of ideas can be viewed as a virus! That is because, when viewed from an evolutionary biology perspective, ideas are the cognitive equivalent of genes (in fact, this is where the term meme comes from).
There's a whole field, evolutionary memetics, dedicated to this. Cultural values, marketing, religion, social media, education, propaganda, etc. can all be viewed quite naturally through this lense. Even the terms we use in every day language (eg, going "viral") seem to intuitively grasp this.
Is my friend a virus for recommending me their favorite book? Well, yes I guess, but that's kind of just how ideas work. Just my two cents