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Carp edema virus disease (CEVD) is an emerging disease of concern to koi enthusiasts and carp Aquaculture in the United States and around the world. Carp edema virus can cause disease and high mortality rates in wild and cultured varieties of common carp (Cyprinus carpio) including koi. Sick fish may exhibit erosive or hemorrhagic skin lesions with swelling (edema) of the underlying tissues, thus the disease was originally named “viral edema of carp” (Oyamatsu et al. 1997a). The disease has also been referred to as “koi sleepy disease” (KSD) because infected fish become lethargic and unresponsive (Miyazaki et al. 2005). The severity of disease is greatest in juveniles, which may hang just under the surface of the water before succumbing, while adult fish may lie motionless on the bottom of the pond/tank.
Carp edema virus disease/koi sleepy disease was first characterized from Japanese koi in 1974 and since has been shown to be widespread across Japan where koi are cultured (Murakami et al. 1976; Ono et al. 1986; Amita et al. 2002). The international trade in koi has likely led to the global spread of CEVD/KSD with outbreaks documented in imported koi in North America and Europe (Hedrick et al. 1997; Way and Stone 2013; Haenen et al. 2013). In the United States, CEVD/KSD has been associated with outbreaks in imported and domestic koi in the following states: California (in the years 1996 and 2010), Washington (2005), North Carolina (2005), Georgia (2005 and 2010), and Florida (2014 and 2015) (Hedrick et al.1997; Waltzek et al. 2014). Carp edema virus has been detected widely across Europe in koi from at least Austria, Czech Republic, France, Germany, the Netherlands, and the United Kingdom (Haenen et al. 2013; Way and Stone 2013; Jung-
What is CEV?
Carp edema virus is a large, double-
What are the signs of CEVD/KSD?
As the common name “koi sleepy disease” implies, CEVD/KSD-
How is a CEVD/KSD diagnosis reached?
In addition to an appropriate case history and clinical signs, further supporting evidence of CEVD/KSD may be obtained by examining wet mounts of the gills. In the early stages of the disease, the gill epithelial cells at the tips of the gill filament proliferate, resulting in a thickening or “clubbing” appearance (Ono et al. 1986; Miyazaki et al. 2005). In CEV-
Observation of microscopic abnormalities from stained slides prepared from formalin-
How do fish get infected with CEV?
In Japan, CEVD/KSD typically occurs in the rainy season among juvenile koi (young-
Which fish are susceptible to CEV?
Common carp and koi (Cyprinus carpio) are the only known susceptible species. However, other species including goldfish (Carassius auratus) have not yet been exposed to CEV in a controlled laboratory setting. Goldfish have been shown to be susceptible to other viral diseases affecting carp/koi such as the rhabdovirus spring viremia of carp (Petty et al. 2012). Interestingly, similar poxvirus-
How does water temperature affect CEV?
Water temperature is an important factor in the occurrence of CEVD/KSD. In Japan, outbreaks in juvenile koi occur in the rainy season from late June to late July at water temperatures between 15 and 25°C (59–77°F) (Oyamatsu et al. 1997a), although many fish also develop CEVD/KSD in the spring and fall (Miyazaki et al. 2005). Outbreaks in koi facilities and hobbyists’ ponds in the United States and the United Kingdom typically occur at similar water temperatures (listed above) (Way and Stone 2013; Waltzek et al. 2014). However, a novel strain of CEV has been associated with UK disease episodes in wild common carp during the winter and early spring at much lower water temperatures, between 6 and 9°C (43–48°F) (Way and Stone, 2013), and similarly in the Netherlands (O. Haenen personal observation). Recently, CEVD/KSD in common carp and koi has also been reported at lower water temperatures between 7–15°C (44–59°F) in Austria (Lewisch et al. 2014).
How can CEVD/KSD be prevented?
Before acquiring any CEVD/KSD-
Quarantine (separation from other uninfected koi) is the most dependable method to avoid the introduction of pathogens into a pond or facility (Yanong and Erlacher-
Is CEV a risk to humans?
Fish viruses do not infect humans and thus CEV is not harmful to humans.
Figure 1; A group of young-
Other external signs of infection may include sunken eyes (enophthalmos) and pale swollen gills (Figure 2, Haenen et al. 2013). These similar external signs (i.e., sunken eyes and gill lesions) may also be observed with another important viral disease of common carp known as koi herpesvirus disease (KHVD) caused by Cyprinid herpesvirus 3 (Hartman et al. 2013). No grossly visible internal disease signs have been reported with CEVD/KSD. The disease is typically observed at water temperatures between 15–25°C (59–77°F) in koi, and at 6–10°C (43–50°F) in common carp and can kill up to 75–100% of juvenile koi during an outbreak (Hedrick et al. 1997; Miyazaki et al. 2005; Way and Stone 2013).
Figure 2; Koi with CEVD/KSD that presented with anorexia (loss of appetite), severe necrosis (cell death) of the gill tissue, and sunken eyes (koi had been frozen).
Figure 3; Transmission electron photomicrograph of a koi gill epithelial cell containing spheroid CEV particles indicated by the arrows.
Within this category of “Fish Health” here on koisale.com we wish to thank Dr. Roy Yanong from the University of Florida IFAS Extension for his permission to utilize much of the information contained here-
Knowing when to seek help or When and How to Look for Fish Veterinarian
This is the website for the American Association of Fish Veterinarians (which several friends and I formed a few years ago, and now has over 130 fish vet members around the U.S.). We are still inputting data for the find-
For more detailed information and the downloadable .pdf file from UF|IFAS