Causative Agent Of Proliferative Kidney Disease Research Articles

Geographic distribution of Tetracapsuloides bryosalmonae infected fish in Swiss rivers: an update

Proliferative kidney disease (PKD) has been recognized as a potential threat to brown trout (Salmo trutta) populations in Switzerland. A study performed in 2000/2001 on 139 sampling sites from 127 rivers in Switzerland revealed a wide distribution of fish infected by Tetracapsuloides bryosalmonae, the causative agent of PKD. The present study aimed to complement this dataset by studying a further 115 sample sites from 91 rivers and 4 fish farms. Mainly brown trout were investigated for the presence of T. bryosalmonae by a combination of macroscopical, histological and immunohistochemical examination. In approximately 56% of the examined sampling sites, T. bryosalmonae-infected fish were found. The prevalence of infected fish at individual sites ranged from 0% to 100%. Infection intensity, judged on the basis of histological and immunohistochemical evaluation for the degree of parasite infection, varied greatly between and within sites. PKD-positive sites were found in all areas of Switzerland. The wide distribution of the disease in Swiss rivers indicates that PKD may be a causative factor for the catch decline of brown trout, which was suggested over recent decades in Switzerland.

Proliferative kidney disease in wild salmonids

The literature on proliferative kidney disease (PKD) in wild fish is briefly reviewed. Results of field and laboratory transmission experiments using brook trout (Salvelinus fontinalis) and grayling (Thymallus thymallus) are presented. Grayling were found to be susceptible to the disease with all fish becoming infected with the PKX parasite (causative agent of PKD) and exhibiting clinical and histopathological signs similar to those seen in PKD-affected rainbow trout. Brook trout exposed to waters enzootic for PKD showed no evidence of the disease or of infection with the PKX parasite. However, laboratory experiments demonstrated that brook trout can be infected with rainbow trout PKX cells and that, although clinical signs of PKD did not develop and PKX cells were not observed, the parasite was able to reach the renal tubule lumens and commence sporogony. Mature spores of PKX were not observed.

Fish infected with Sphaerospora spp. Thélohan (Myxosporea) from waters enzootic for proliferative kidney disease of salmonids.

Sphaerospores were found among three species of fish examined from waters known to be enzootic for proliferative kidney disease (PKD) of salmonids. They were detected in the renal tubules of both hatchery-reared rainbow trout (Salmo gairdneri) exposed to the infectious stage of PKD and in chubs (Gila bicolor) in the headwaters of a hatchery where PKD is enzootic. Sticklebacks (Gasterosteus aculeatus) collected near net pens where Pacific salmon had experienced a PKD epizootic were also found to harbor sphaerospores in the lumen of the kidney tubules. The latter two host species contained developmental stages of a myxosporidan in the blood and in the lumen of the kidney tubules which are similar to those of PKX, the causative agent of PKD in salmonid fish. The sphaerospores observed in the rainbow trout are the first to be observed in this species. The similarity to previously observed developmental stages, rarity, and presence of these sphaerospores in salmonid fish from a hatchery where PKD is enzootic suggest that they are the most mature stage of the PKX myxosporidan yet observed.