Carp edema virus from three genogroups is present in common carp in Hungary

Hungary is an important carp producer with intensive trading relationships with farms in other carp-producing areas in Europe. Carp in Europe were recently found infected with carp edema virus (CEV), a poxvirus which causes the koi sleepy disease (KSD) syndrome. Moribund carp were collected from 17 fish farms and angling ponds in different regions of Hungary. Histological analysis of gills from these carp revealed a proliferation of the interlamellar epithelium and an infiltration by eosinophilic cells. In 13 of 17 of these carp, CEV DNA was detected by qPCR and in seven fish more than 1 × 10⁴ copies of virus-specific DNA sequences per 250 ng of DNA, which could be considered as clinically relevant and a cause of disease. A phylogenetic analysis of the sequences revealed that all three genogroups of CEV were present in Hungarian common carp with genogroup I being most abundant. These results support the hypothesis of a prolonged presence of CEV in European carp populations and suggest that previous outbreaks of KSD were not recorded or misdiagnosed. Hence, a testing of carp and koi for infection with CEV should be included into disease surveillance programmes to prevent further spreading of this disease.