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

Abstract

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.