Spring Viremia Of Carp (VVK, SVC)

Spring Viremia Of Carp (VVK, SVC)
Spring Viremia Of Carp (VVK, SVC)
Anonim

Spring viremia of carp (SVC) is a viral disease of some species of pond fish, characterized by an acute course with manifestation of body edema, ruffled scales, one- or two-sided bulging eyes, the presence of punctate or focal hemorrhages at the base of the pectoral and abdominal fins.

Etiology. The causative agent is a bullet-shaped RNA-containing virus with a particle size of 105-125x70-85 nm, belonging to the group of rhabdoviruses. The virus multiplies in primary trypsinized cell cultures of carp gonads and in transplanted fish cell lines that are widely used in ichthyopathology. Virus reproduction is accompanied by a clearly pronounced cytopathogenic effect with complete destruction of the monolayer within 2-4 days.

The virus multiplies in cell culture at temperatures from 19-22 ° C to 25 ° C, and at 4 ° C, its reproduction stops. The virus is not resistant to ether and chloroform, it is sensitive to pH 3.0. Heating at 60 ° C leads to complete inactivation of the virus within 30 minutes. At 4 ° C, it can persist for about a year in an environment with a pH of 7.4-7.6. In organs of diseased fish preserved with 50% phosphate buffered saline of glycerol, the virus persists for at least 6 months.

Epizootological data. The spring viremia of carp was first described by the Yugoslav researcher N. Fian (1968), and in subsequent years it was registered in Hungary, Czechoslovakia, Germany and other European countries. In Russia, this disease appeared in the mid-70s under the name spring viral fish disease (Rudikov, 1985).

Carps, silver carp and silver carp and grass carp are ill. Clinically, the disease manifests itself only in yearlings of the indicated species of fish, cultivated in pond fish farms.

The VVK is characterized by seasonality. Its outbreaks in natural conditions are noted only in early spring at a temperature in reservoirs of 10-14 ° C. The onset of the disease coincides with the transfer of yearlings of pond fish from wintering ponds to feeding ponds. The disease lasts 1-1.5 months, then, with an increase in the water temperature in the feeding ponds to 18-20 ° C, it spontaneously stops.

Carps sick with spring carp viremia, photo photograph of fish disease
Carps sick with spring carp viremia, photo photograph of fish disease

Carp sick with spring carp viremia. Photo Andy Goodwin, UAPB Aquaculture / Fisheries Center

It was found that the manifestation of the disease in fish is associated with stress factors. Their influence is noted both during the wintering of fish in wintering ponds (transplants, oppressed conditions, antiparasitic treatments, etc.), and in the first days after transplanting it into feeding ponds (injury during transportation, the presence of pesticides and other components in the water. surface runoff entering ponds in spring, deficiency of oxygen dissolved in water, increased oxidizability, etc.). Under such unfavorable ecological and zoohygienic conditions, the extent of infection can reach 20-40% and be accompanied by the death of diseased fish. With the elimination of all the above stress factors, the disease does not manifest itself for many years, even in farms that were previously unfavorable in terms of IHC. Hence,Although this disease has a specific pathogen - rhabdovirus, it manifests itself only under certain environmental and zoological conditions.

Symptoms. The incubation period for natural infection in fish ponds, depending on the temperature, ranges from 7 to 30 days.

At the onset of the disease, the behavior of carp changes: sick fish accumulate in shallow areas of the pond, swim in a circle or in a corkscrew manner, refuse to feed. With the development of the pathological process in fish, diffuse or focal ruffling of the scales, swelling of the abdomen, punctate hemorrhages or spotty redness at the bases of the pectoral and pelvic fins, one- or two-sided bulging eyes appear. Sometimes in carp darkening of the skin, dryness and roughness of the skin, anemia of the gills are noted. In some cases, the presence of sickle hemorrhages in the eyeball is established in patients.

In herbivorous fish, the symptoms of the disease are almost the same as in carp, but they are less pronounced.

Pathological changes and pathogenesis. At autopsy in sick fish, a widespread edema of the body is noted, an accumulation of yellowish fluid in the abdominal cavity, sometimes with an admixture of blood, edema of internal organs. The liver is enlarged, unevenly colored: pale or spotty. sometimes with punctate hemorrhages and whitish nodules. The kidneys are swollen, flabby, rarely with spotted hemorrhages. The spleen of most fish is enlarged, K-shaped, dark cherry in color; in some fish, grayish tubercles or spots are found under the capsule. The intestines are usually empty, with symptoms of catarrhal inflammation and rare punctate hemorrhages on the mucous membrane.

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