title: Long-term epidemiological survey of Kudoa thyrsites (Myxozoa) in Atlantic salmon (Salmo salar L.) from commercial aquaculture farms.
abstract: Kudoa thyrsites (Myxozoa) encysts within myocytes of a variety of fishes. While infected fish appear unharmed, parasite-derived enzymes degrade the flesh post-mortem. In regions of British Columbia (BC), Canada, up to 4-7% of fillets can be affected, thus having economic consequences and impacting the competitiveness of BC's farms. K. thyrsites was monitored in two farms having high (HP) or low (LP) historical infection prevalence. At each farm, 30 fish were sampled monthly for blood and muscle during the first year followed by nine samplings during year two. Prevalence and intensity were measured by PCR and histology of muscle samples. In parallel, fillet tests were used to quantify myoliquefaction. Infections were detected by PCR after 355 and 509 degree days at LP and HP farms, respectively. Prevalence reached 100% at the HP farm by 2265 degree days and declined during the second year, whereas it plateaued near 50% at the LP farm. Infection intensities decreased after 1 year at both farms. Blood was PCR-positive at both farms between 778 and 1113 degree days and again after 2000 degree days. This is the first monitoring project in a production environment and compares data between farms with different prevalence.
authors.affiliation: BC Centre for Aquatic Health Sciences, Campbell River, BC, Canada.
authors.forename: W L
authors.initials: WL
authors.lastname: Marshall
authors.affiliation: Instituto de Acuicultura de Torre de la Sal (IATS-CSIC), Castellón, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Sitjà-Bobadilla
authors.affiliation: BC Centre for Aquatic Health Sciences, Campbell River, BC, Canada.
authors.forename: H M
authors.initials: HM
authors.lastname: Brown
authors.affiliation: Marine Harvest Canada, Campbell River, BC, Canada.
authors.forename: T
authors.initials: T
authors.lastname: MacWilliam
authors.affiliation: BC Centre for Aquatic Health Sciences, Campbell River, BC, Canada.
authors.forename: Z
authors.initials: Z
authors.lastname: Richmond
authors.affiliation: Ministry of Forests, Lands and Natural Resource Operations, Fish and Wildlife Branch, Cranbrook, BC, Canada.
authors.forename: H
authors.initials: H
authors.lastname: Lamson
authors.affiliation: Instituto de Acuicultura de Torre de la Sal (IATS-CSIC), Castellón, Spain.
authors.forename: D B
authors.initials: DB
authors.lastname: Morrison
authors.affiliation: School of Life and Environmental Sciences, Centre for Integrative Ecology, Warrnambool Campus, Deakin University, Geelong, Vic., Australia.
authors.forename: L O B
authors.initials: LO
authors.lastname: Afonso
mesh_terms: D000818:Animals; D017756:Aquaculture; D001955:British Columbia / Q000453:epidemiology; D005260:Female; D005393:Fish Diseases / Q000453:epidemiology* / Q000469:parasitology; D005843:Geography; D008297:Male; D009132:Muscles / Q000469:parasitology; D055764:Myxozoa / Q000235:genetics / Q000502:physiology*; D018512:Parasitemia / Q000453:epidemiology / Q000469:parasitology / Q000662:veterinary*; D010273:Parasitic Diseases, Animal / Q000453:epidemiology* / Q000469:parasitology; D016133:Polymerase Chain Reaction / Q000662:veterinary; D015995:Prevalence; D020317:Salmo salar; D012621:Seasons
keywords: histopathology; immunity; intensity; myoliquefaction; prevalence; pseudocysts