Experimental infections of different carp strains with the carp edema virus (CEV) give insights into the infection biology of the virus and indicate possible solutions to problems caused by koi sleepy disease (KSD) in carp aquaculture

Table 1 Occurrence of KSD clinical sings during cohabitation experiments

Cohabitation experiment no.	CEV genogroup	Observation day	Development of KSD clinical signs (no. of fish)				Severity of histological changes
Cohabitation experiment no.	CEV genogroup	Observation day	Koi	PS	Rop	AS	Koi	PS	Rop	AS
Co I	Genogroup I	15	5/5	4/5	n.d.	n.d.	+/++*	+/++*	n.d.	n.d.
Co II	Genogroup I	11	7/7	7/7	2/7	0/7	+/++	++/+++	++	+/++
Co IV	Genogroup IIa	11	4/4	0/4	0/4	0/4	+/++	+/++	+/++	++

Number of fish which developed clinical signs (lethargy, laying on the bottom of the tank) associated with KSD at the last day of cohabitation experiment, symbol “n.d.” indicates that this particular carp strain was not evaluated. Severity of histological changes which was semiquantitatively graded, which is indicated with following symbols: “−” no histological lesion; “+” mild histological changes; “++” moderate histological changes; “+++” severe histological changes. Symbol “*” indicates that histological analyses was performed at day 6, which was not the last day of infection.

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