The Carp edema virus was first described in Japan in 1974 and also in Germany in 2014 and belongs to the family Poxviridae. Three different CEV lines have been identified that can lead to clinical signs in koi and carp. Koi Sleepy Disease usually occurs in the range of 15 – 25 °C, especially in carp, but also at much lower temperatures. The incubation period depends on the water temperature. Signs are lethargy andlying motionless on the ground.Additionally, there may be erosive or haemorrhagic skin lesions with oedema of the underlying tissue as well as an excessive production of mucous on skin and gills.Secondary infections are possible.
In differential diagnosis, koi herpesvirus (KHV), spring viraemia of carp (SVC), a high organic load of the water and infestation with ectoparasites need to be considered.