Polyinosinic:polycytidylic acid (Poly(I:C)), a synthetic analog of double-stranded RNA and a potent activator of TLR3, has been shown to mimic a viral infection and is able to evoke a classic sickness response, including hypophagia and decreased locomotor activity, when systemically or centrally administered to mice31,32. Here, TLR3 is linked to viral infectious disease.