What is KSD (Koï Sleepy Disease)?

Commonly known as carp sleeping sickness, it is a new contagious viral disease caused by the Carp Edema Virus (CEV), possibly belonging to the Poxvirus family. Appeared in Japan in 1974, it now affects Europe (detection in the United Kingdom, the Netherlands, France).

It affects Cyprinus carpio (common carp and koi carp), but to date, there is no certainty about the absence of carriage by other species.

Mortality can be significant and reach 80% in a few days (1 to 2 weeks). The trigger temperature is typically between 15 and 25°C in koi carp, or at a lower temperature (6-10°C) in common carp.

Clinical signs

• Lethargy, sometimes at the bottom of the water, sometimes at the surface or at the edge of the pool. Most often lateral decubitus. Apparent death, except the eyes which remain active. The carp reacts to stimulation, but falls back into lethargy shortly after. At an advanced stage, no more reaction after stimulation.
• Hypersecretion of mucus at the beginning of the disease.
• Swelling due to edema.
• Enophthalmos (eyes retracted into the sockets), sometimes with ocular hemorrhages.
• In the terminal phase may be observed: loss of skin mucus, epidermal erosion, skin hemorrhages and significant necrosis of the gills

Transmission

The disease is very contagious and is transmitted from fish to fish through fish carrying the virus (sick or not), contaminated equipment (dip nets), water, feces, sludge, sediments… Measures for an affected aquarium are outlined in the aquarium disinfection FAQ.

Fish could harbor the virus for a very long time without being sick. Temperature is then a key factor in triggering the disease, although other factors can certainly be determining (stress, etc.).

What to do if the disease is identified?

If the presence of virus is confirmed by molecular biology (PCR), it is recommended to take measures to stop its spread: partitioning, or even elimination of fish, disinfection of tools and structures, etc.

There is no vaccine.

Animal health status

WOAH considers CEV infection an emerging disease to be reported by veterinary authorities under its Aquatic Code. It is distinct from koi herpesvirus disease (KHV), which is listed in category E under EU Implementing Regulation 2018/1882 (French summary). This EU classification applies within the European Union.