There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.
Abstract
The myxozoan parasite Ceratomyxa shasta infects salmonids causing ceratomyxosis, a
disease elicited by proliferation of the parasite in the intestine. This parasite
is endemic to the Pacific Northwest of North America and salmon and trout strains
from endemic river basins show increased resistance to the parasite. It has been suggested
that these resistant fish (i) exclude the parasite at the site of invasion and/or
(ii) prevent establishment in the intestine. Using parasites pre-labeled with a fluorescent
stain, carboxyfluorescein succinimidyl diacetate (CFSE), the gills were identified
as the site of attachment of C. shasta in a susceptible fish strain. In situ hybridization
(ISH) of histological sections was then used to describe the invasion of the parasites
in the gill filaments. To investigate differences in the progress of infection between
resistant and susceptible fish, a C. shasta-susceptible strain of rainbow trout (Oncorhynchus
mykiss) and a C. shasta-resistant strain of Chinook salmon (Oncorhynchus tshawytscha)
were sampled at consecutive time points following exposure at an endemic site. Using
ISH in both species, the parasite was observed to migrate from the gill epithelium
into the gill blood vessels where replication and release of parasite stages occurred.
Quantitative PCR verified entry of the parasite into the blood. Parasite levels in
blood increased 4days p.i. and remained at a consistent level until the second week
when parasite abundance increased further and coincided with host mortality. The timing
of parasite replication and migration to the intestine were similar for both fish
species. The field exposure dose was unexpectedly high and apparently overwhelmed
the Chinook salmon's defenses, as no evidence of resistance to parasite penetration
into the gills or prevention of parasite establishment in the intestine was observed.
Copyright 2010 Australian Society for Parasitology Inc. Published by Elsevier Ltd.
All rights reserved.