A piscine myocarditis virus (PMCV) virus-like particle (VLP) is disclosed which consists only of PMCV open reading frame 1 (ORF1) protein. Methods of producing the VLPs consisting only of ORF1 are also disclosed, wherein the methods comprise infecting an insect cell with a baculovirus expression vector encoding PMCV ORF1, and incubating the infected cell to allow the expression of PMCV ORF1 protein and the production of PMCV VLP. The insect cell is preferably incubated at a temperature of 12-20oC, particularly 15 oC (i.e. below the temperature conventionally used in baculovirus expression systems). Baculovirus expression vectors encoding the PMCV ORF1 protein, and insect cells comprising such vectors, are also claimed.
