Complex interaction between proliferative kidney disease, water temperature and concurrent nematode infection in brown trout

Abstract

Proliferative kidney disease (PKD) is a temperature-dependent disease caused by the myxozoan Tetracapsuloides bryosalmonae. It is an emerging threat to wild brown trout Salmo trutta fario populations in Switzerland. Here we examined (1) how PKD prevalence and pathology in young-of-the-year (YOY) brown trout relate to water temperature, (2) whether wild brown trout can completely recover from T. bryosalmonae-induced renal lesions and eliminate T. bryosalmonae over the winter months, and (3) whether this rate and/or extent of the recovery is influenced by concurrent infection. A longitudinal field study on a wild brown trout cohort was conducted over 16 mo. YOY and age 1+ fish were sampled from 7 different field sites with various temperature regimes, and monitored for infection with T. bryosalmonae and the nematode Raphidascaris acus. T. bryosamonae was detectable in brown trout YOY from all sampling sites, with similar renal pathology, independent of water temperature. During winter months, recovery was mainly influenced by the presence or absence of concurrent infection with R. acus larvae. While brown trout without R. acus regenerated completely, concurrently infected brown trout showed incomplete recovery, with chronic renal lesions and incomplete translocation of T. bryosalmonae from the renal interstitium into the tubular lumen. Water temperature seemed to influence complete excretion of T. bryosalmonae, with spores remaining in trout from summer-warm rivers, but absent in trout from summer-cool rivers. In the following summer months, we found PKD infections in 1+ brown trout from all investigated river sites. The pathological lesions indicated a reinfection rather than a proliferation of remaining T. bryosalmonae. However, disease prevalence in 1+ trout was lower than in YOY.

Proliferative kidney disease (PKD) agent Tetracapsuloides bryosalmonae in brown trout populations in Estonia

“…In fact, we observed a significant increase in T. bryosalmonae prevalence in 1+ and older fish for the whole data set (Wilcoxon signed ranks test) as well as for 4 individual comparisons (2×2 contingency table). These results are in line with a recent study by Schmidt-Posthaus et al (2013), who found a similar pattern of high T. bryosalmonae prevalence in 1+ trout in a Swiss river system. According to SchmidtPosthaus et al (2013), the pathological lesions in 1+ trout, such as acute gill and kidney lesions, indicate re-infection rather than proliferation of the remaining parasites.…”

“…According to SchmidtPosthaus et al (2013), the pathological lesions in 1+ trout, such as acute gill and kidney lesions, indicate re-infection rather than proliferation of the remaining parasites. It is therefore likely that a higher prevalence of T. bryosalmonae observed in this study was caused by re-infection of 1+ trout during the second summer while lack of clinical signs suggest partial immunity of 1+ fish (Schmidt-Posthaus et al 2013). 145 Dis Aquat Org 109: 139-148, 2014 We also detected T. bryosalmonae infection in the middle and posterior part of the kidney in 3 returning adult sea trout spawners.…”

Distribution and prevalence of T. bryosalmonae in Austria: A first survey of trout from rivers with a shrinking population

“…The fact that similar results were obtained testing higher temperature thresholds can be taken as a hint that infection is in fact related to extended periods of water temperatures higher than 15°C. Several other studies could not prove a correlation between temperature and site‐specific prevalence of T. bryosalmonae (Carraro et al., ; Schmidt‐Posthaus, Steiner, Müller, & Casanova‐Nakayama, ; Wahli, Bernet, Segner, & Schmidt‐Posthaus, ). Temperature data were not available from all rivers, especially data from some upstream locations are missing, which were free of the parasite and most likely exhibit low water temperatures.…”

Impact of Thermal Stress on Kidney-Specific Gene Expression in Farmed Regional and Imported Rainbow Trout

“…Moreover, it is comprised of hematopoietic and lymphoid tissue, exerting immunological functions (Zapata et al 2006). The latest research on teleost kidney mainly focuses on the clinical aspects of infections, such as the bacterial kidney disease (Schmidt-Posthaus et al 2013), investigations on the expression of immune relevant genes in head kidney leukocytes (Villarroel et al 2013) and the regulation of cortisol release (Conde-Sieira et al 2013).…”