"Virus" is a song by Icelandic artist Björk released as the first promotional single from the album Biophilia. Each song in the album features a theme related to nature. In "Virus", Björk explores "fatal relationships" such as the one between a virus and a cell, as Björk explained in an interview: "It's a kind of a love story between a virus and a cell. And of course the virus loves the cell so much that it destroys it."
"Virus" features a gameleste (a hybrid between a celesta and a gamelan that can be controlled by midi and that was also used in "Crystalline", built exclusively for these songs) base that plays through the whole song. The gameleste represents the 'virus' that continues multiplying until it takes control at the end of the song. Also, Manu Delago plays hang drum. Since Björk wanted the album to break the typical 4/4 time signature, "Virus" has a time signature of 3/4.
The lyrics to "Virus" talk about "dangerous relationships", symbiotic relationships in which one organism is parasite for the other and takes a benefit, even changing the other's behaviour. This fact is used as a metaphor between 'love' and 'parasiting'. Björk took inspitation from a McGraw-Hill educative video about mind-controlling parasites and from candidiasis, illness that she suffered
"I'd been fighting this candida issue in my throat and I had to really change my diet and use different medication and it sort of seems to pop up and its kinda hilarious. It’s like I have this new neighbour that I have to sort of learn to live with. And obviously you know this fungus is inside all of us and it’s never about eliminating it. You have to kind of just live with it.”