“Comparative assessment of Great Lakes salmonids pathobiology upon Tetracapsuloides bryosalmonae infection ” (7349)

Comparative assessment of Great Lakes salmonids pathobiology upon Tetracapsuloides bryosalmonae infection

Introduction

The geographic distribution of the myxozoan Tetracapsuloides bryosalmonae (Malacosporea) in North America is being reconsidered, following our recent discovery that this parasite may be infecting a variety of salmonids across the Great Lakes watershed. Asymptomatic fishes with low parasite burdens are found in this region, although Proliferative Kidney Disease (PKD), a severe chronic lymphoid immunopathology, is not seen yet. Based on studies on European fishes, Rainbow Trout (Oncorhynchus mykiss) juveniles have been traditionally considered the most susceptible hosts to suffer PKD and cannot propagate T. bryosalmonae lifecycle (occurrence of histozoic extrasporogonic sporulation). Brown Trout (Salmo trutta) are instead considered a more tolerant host, able to propagate T. bryosalmonae lifecycle (coelozoic sporogony in renal tubules).

Methodology

Tetracapsuloides bryosalmonae infection was confirmed by PCR (targeting the parasite 18S rDNA) using posterior kidney sampled from migratory Chinook (O. tshawytscha) and Coho Salmon (O. kisutch), and Rainbow and Brown Trout. The occurrence of histozoic and coelozoic T. bryosalmonae stages was searched in PCR-positive specimens. A new immunohistochemistry protocol was optimized using a new antibody specific to the parasite to improve the visualization of T. bryosalmonae in histological sections in the absence of PKD.

Results

Due to the low parasite burden (10^{^3}/10^{^5}/g kidney), and lack of PKD, the histological identification of parasitic stages was challenging. Histology and IHC observations provide new evidence that both sporogonic and extrasporogonic stages of T. bryosalmonae are occurring in these species.

Conclusions

We comparatively examined histological preparations towards the definition of susceptibility/tolerance patterns in freshwater-adapted salmonids retrieved from the Great Lakes region. These findings revealed that all these Great Lakes salmonids may act as tolerant or partially susceptible hosts and could potentially propagate the parasite lifecycle. Considering the higher parasite strain diversity and wider range of salmonid species in North America, the traditional PKD host-susceptibility paradigm may need to be reconsidered.

1. Fusianto, Cahya K., Fish Pathobiology and Immunology Laboratory, College of Veterinary Medicine, Michigan State University, East Lansing, MI, USA, Author
2. GORGOGLIONE, BARTOLOMEO, Fish Pathobiology and Immunology Laboratory, College of Veterinary Medicine, Michigan State University, East Lansing, MI, USA, Presenter