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International Waters: ‘Sleepy’ Koi Reach Austria


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Anyone could be forgiven for thinking that any common carp or koi (Cyprinus carpio) affected by lthargy, enophthalmia (sunken eyes), skin erosion and gill damage, and accompanied by up to 80 percent mortality is suffering from koi herpesvirus disease (KHV), but they could be wrong.

The fact is that these symptoms also are associated with koi sleepy disease (KSD), a serious ailment first discovered in Japan in the 1970s. Originally described as a viral oedema that affected juvenile carp, this pox virus caused the juvenile carp to gasp for air at the water surface or near water inflows into ponds. More recently, the same pox virus, called carp edema virus (CEV), was found in older fish, which, in contrast to the juveniles, tended to lie on the pond bottom, where they eventually died from lack of oxygen.

Since its discovery in Japan, the disease has been detected in several countries, including France, Germany, the Netherlands and the U.K. However, we now have news of a first outbreak of koi sleepy disease in both carp and koi in Austria. Although this first outbreak was reported in February 2015, analysis of archived genetic material has revealed that KSD/CEV has been present in Austria since at least 2010.

This ties in with observations of high koi and carp mortalities every spring for several years now. KSD/CEV is not the only koi viral disease that causes high mortality. KHV and spring viraemia of carp (SVC) do likewise, but the fact that its presence now has officially been confirmed opens the door to this emergent disease coming under the spotlight.

It’s possible the virus mutated from the original form and is now better suited to European conditions than it originally was. This line of thinking is gathering momentum because of temperature differences between European ponds and their Japanese counterparts, at least as far as common carp are concerned.

In Europe, carp live in waters ranging between 7 degrees Celsius and 15 degrees Celsius, but in Japan, typical koi pond temperatures tend to range between 15 degrees Celsius and 25 degrees Celsius. As European carp apparently succumb to KSD/CEV at lower temperatures than their cultivated Japanese cousins, this is being taken as an indication that there’s been a mutation somewhere along the way that has allowed the virus to adapt to European conditions.

The emergence of KSD/CEV is considered so serious that a whole workshop was dedicated to it at the European Association of Fish Pathologists (EAFP), which held its annual conference in September. The outcome has not yet been made public.

As things stand now, KSD/CEV is not a notifiable disease, meaning there isn’t yet a legal requirement to notify the relevant authorities of any outbreaks. Indeed, there are relatively few fish diseases that fall into this category. The World Organization for Animal Health only lists nine, among which we find SVC and KHV, while the U.K. authorities (which impose strict health standards) also list just nine, only three of which, SVC, KHV and epizootic ulcerative syndrome, affect ornamental fish.

This could change, with KSD/CEV being proposed for consideration as a notifiable disease in the near future. If this happens, then proposals to set the relevant wheels in motion are likely to be tabled at gatherings, such as the EAFP workshop.  


This article originally appeared in the October 2015 issue of Pet Product News.

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