In recent years, mortality of common carp increased in some Czech and Moravian ponds during spring months. Similar problems have also occurred in other European countries which are engaged in the breeding of common carp (Germany, Austria, Poland, the Netherlands, Great Britain, ect.). In most cases, a virus similar to that what has been considered as the causal agent of the so-called "koi sleepy disease" in ornamental fish in Japan since the 1970s has been recently detected in the tissues of diseased and dead carp in Europe. Edema of different tissues was one of the accompanying symptoms of this disease, the causal agent has been called "Carp Edema Virus", CEV abbreviated (it does not yet have an adequate Czech name). Infected fish have breathing problems, gather at the surface or inflow, and sometimes "blow". They also lose escape reflex, are lethargic, sleepy, and can be caught by hands. Lighter patches appear on the skin, the eyes appear to be sunken and the gills are light with necrotic parts, sometimes covered with gray-green mold. So far, this disease has only been recorded with carp. With this narrow host specificity and typical symptoms, this disease is very similar to other viral infections, namely koi herpesvirus disease (KHVD). However, there are two major practical differences. First, CEV disease usually occurs at 8-18 ° C, while KHVD outbreaks most commonly at 23 ° C. Second, the disease caused by the CEV is not among the monitored fish diseases, whereas the KHV is on the list of so-called "dangerous diseases", which are subject to certain strict veterinary measures.
Many research centers have already begun to deal with the "CEV". It has been found, among other things, that the virus found in Japanese koi carp suffering from sleepy disease is slightly genetically different from the virus detected in infected common carp in Europe. Researchers from FROV JU participated with their colleagues from Germany, Great Britain and Poland in the research study which has shown that healthy fish kept in tanks together with infected ones have a different sensitivity to two existing variants of the virus: Koi carp was more easily infected from diseased koi and were more resistant to the "carp" virus, whereas common carp were more susceptible to infection transmitted by sick common carp, while they were relatively immune to the virus excreted by diseased koi. At the same time, differences in susceptibility to viruses in different strains of carp were showed. Similar to the KHVD, also in case of CEV, higher resistance of the Amur wild carp, a wild form of carp originally living in the Amur River basin, has been clearly demonstrated. It can be assumed that the strains which have the Asian ancestor in their pedigree, such as the Ropsha scaly carp or Amur mirror carp, will also exhibit higher resilience and survival if CEV will expand in our territory.
For more information on this issue, see Adamek, M., Oschilewski, A., Wohlsein, P., Jung Schroers, V., Teitge, F., Dawson, A., Gela, D., Piačková, V., Kocour, M., Adamek, J., Bergmann, S. M., Steinhagen, D. 2017. 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. Veterinary Research 48: 12.
