Fish proliferative kidney disease

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The Proliferative kidney disease of fish (engl. Proliferative kidney disease , PKD ) is a parasitic disease in fish, by abdominal swelling, enlargement of the kidneys , dark discoloration and a protrusion of the eyeball ( exophthalmos is marked). It is a reportable animal disease in Switzerland .

Pathogen and occurrence

The causative agent of proliferative kidney disease is Tetracapsuloides bryosalmonae , a parasitic cnidarians from the tribe of the Myxozoa . The parasite required as intermediate host bryozoans ( Bryozoa ) in which infectious spores develop, the only survive in open water one day. The fish are infected through the gills and skin. This then leads to an increase in the kidneys. Excretion of spores from fish has not yet been proven, so that fish may only represent a false host . Stress can make the disease more likely to break out.

The pathogen occurs in Europe and America. Trout fish (salmonids), grayling and pike are considered susceptible . The disease has been known since the late 1970s. The increasing pollution of the waters is presumably mainly driven by the fish stock .

Clinical picture

Clinical symptoms only occur if the water temperature is above 15 ° C for at least two weeks, so that an infestation only manifests itself from July to September. The incubation period is about six weeks. Infested fish become listless, turn dark and show a swelling of the abdomen. Often there is also a protrusion of the eyeballs.

The mortality rate is around 10 to 15%, in exceptional cases it can be up to 90%. In England the disease is blamed for about 50% of the losses in rainbow trout farming.

After opening, greatly enlarged, nodular kidneys appear in the abdominal cavity. Pathohistologically, it is an interstitial nephritis with formation of connective tissue and, in some cases, a granulomatous inflammation . The parasites appear as large cells. Other internal organs can also be affected by inflammation.

Combat

There is no effective therapy or prophylaxis . The control is therefore limited to epidemic hygiene measures, in particular by carrying out stocking measures only with animals from recognized free breeding. In Switzerland, proliferative kidney disease is notifiable.

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