It was attributed to a combination of adverse environmental factors together with the presence of bacteria of the genus Vibrio and the presence of the Ostreid herpesvirus-1 (OsHV-1) including a newly described genotype of that virus named OsHV-1 μvar.
Selle põhjustajaks peeti mitme ebasoodsa loodustingimuse koosmõju Vibrio perekonda kuuluva bakteri ja austrite herpesviirusega-1 (OsHV-1), sh selle viiruse hiljuti kirjeldatud genotüübiga OsHV-1 μvar.