In June, Tiebo wrote a blog about the fact that Yoshikigoi is now allowed to export Koi to England after a very long run-up. The reason it took a long time before permission was granted had to do with the need for an exemption for Spring Viraemia of Carp (SVC). A whole new field for Europe. But what is SVC and why is it necessary that there is certainty that, in addition to KHV, the Koi farm is also free of SVC?
SVC is caused by infection with the Spring Viraemia or Carp virus (SVCV), which belongs to the Rhabdoviradae virus family. The virus was first detected in Yugoslavia, in 1971, but has already been found in many European countries, including England, Denmark, Germany, the Netherlands and Spain. The virus infects not only Koi, but actually all cyprinids. SVCS looks like a very small bullet, about 150 nanometers long. To give you an idea, that is about 100 times smaller than the parasite costia.
The virus is very contagious and deadly, especially for young fish. Mortality can be as high as 70% and especially in the food industry (carp for consumption) this can lead to major economic losses. For this reason, among others, SVC has been obliged to report for a number of years (within 48 hours of diagnosis) to the World Organization for Animal Health (OIE, Office International des Epizooties). In Japan, Koi breeders must also be demonstrably KHV and SVC free, and there is regular monitoring of this.
Mortality due to SVC can be as high as 70% among young fish
In general, young fish, up to 1 year old, are particularly susceptible to the disease. Although carp of all ages can get sick. In general, the fish infect each other (‘horizontal’ infection), although it cannot be ruled out that the transmission of the virus also occurs via eggs (‘vertical’ infection). There are also indications that larger parasites, such as carp lice and anchor worms, can transmit the virus.
SVC breaks out especially in spring (hence the name, spring is the English word for spring), when the water temperature is between 11 and 17 degrees Celsius. Disease outbreaks are hardly seen below 10 degrees, and mortality decreases when the temperature rises above 22 degrees Celsius. Secondary infections, for example by parasites or bacteria, can play a role in the degree of mortality. The outbreak of SVC in the spring is mainly seen in countries with a cold winter and there are indications that a poor condition of overwintered fish is partly the cause in the case of disease.
(photo: Andy Goodwin, UAPB Aquaculture/Fisheries Center)
When the disease breaks out, it is mainly noticeable because of the large increase in mortality among carp. The downside is that the symptoms are often non-specific to SVC. This means that the symptoms could also indicate other conditions. Examples of possible symptoms include: bulging eyes, abdominal distention, dark color of the body, pale gills, bleeding in the skin and gills, and a protruding anus. Young fish can be lethargic and suffer from balance problems. The affected organs are mainly the gills, liver, kidneys and spleen. However, it can also happen that the fish die suddenly without any symptoms ever being observed.
If there is a suspicion that fish are infected with SVCV, because of a rapid and massive mortality, various tests are possible that show whether there is indeed SVC. In the event of a positive test for SVCV, a report will have to be made and a culling will have to be carried out. To prevent outbreaks, it is important to take proper hygienic measures, such as regular disinfection of the ponds, disinfection of equipment when exchange between ponds, disinfection of eggs and minimization of stress.
A vaccine for SVCV is being worked on
Fish that survive SVC can develop antibodies against the virus, so that they do not become ill in the event of a new outbreak. The fact that this is possible means that it is possible to vaccinate fish. A lot of work is being done on possible vaccines, but for that to happen, more needs to be known about the mechanism behind the disease SVC, in other words, how the virus makes the carp so sick.
