Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish

Perkinsus sp. of Oysters in the Pacific and Southern oceans

Category | Common Name | Scientific Name | Distribution | Host Species
Impact on Host | Diagnostic Technique | Methods of Control | References | Citation

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Category

Category 1 (Not Reported in Canada)

Common, generally accepted names of the organism or disease agent

Perkinsus of oysters in the Pacific and southern oceans.

Scientific name or taxonomic affiliation

a) Perkinsus beihaiensis (Moss et al. 2008a).
b) Perkinsus sp. with genetic similarities to P. beihaiensis (Sabry et al. 2009).
c) Perkinsus-like protist (Norton et al. 1993).

Geographic distribution

a) The type locality was designated as Beihai region, Guangxi Zhuang, China. Based on oyster samples examined by a P. beihaiensis-specific PCR assay, the geographic distribution extends along the southern coast of China at least from Tong'an in Fujian province to Qinzhou and locations surrounding Beihai, Guangxi province (Moss et al. 2008a).
b) Pacoti River estuary in the state of Ceará, northeast Brazil (Sabry et al. 2009).
c) Great Barrier Reef, Australia (Goggin and Lester 1987). Also, oysters collected from the Cooktown area of the Great Barrier Reef off the coast of northern Queensland, Australia were found infected after being transplanted to and held for 12 months on a farm in Torres Strait, Australia (Norton et al. 1993).

Host species

a) Crassostrea hongkongensis (type host) and Crassostrea ariakensis. Also, detected by a P. beihaiensis-specific PCR assay in Pinctada margaritifera and Pinctada martensii pearl oysters and some unidentified bivalve mollusc species from the same location as infected oysters (Moss et al. 2008a). Crassostrea virginica and Mercenaria mercenaria were found susceptible via experimental cohabitation in the laboratory (Moss et al. 2008b).
b) Crassostrea rhizophorae (Sabry et al. 2009).
c) Pinctada margaritifera, Pinctada sugillata and Pinctada maxima pearl oysters and the subtidal oysters Alectryonella plicatula and Malleus regula (Goggin and Lester 1987, Norton et al. 1993).

Impact on the host

a) Perkinsus beihaiensis was initially detected in Asian oysters being assessed for pathogens and diseases prior to assessment for potential introduction into Chesapeake Bay, USA for the restoration of the severely depleted Crassostrea virginica populations (Moss et al. 2007). Prevalence as high as 60% was detected in affected oyster populations. Histopathological observations of defensive haemocyte infiltration into infected tissue and the occurrence of P. beihaiensis in the epithelial regions of the stomach, intestine and digestive tubules and ducts suggest that infection is detrimental to oysters and could potentially lead to interference with nutrient uptake (Moss et al. 2008a). Also, a few moribund or dead oysters were found to have very heavy infection intensities (Moss et al. 2008a). However, there are no reports of apparent disease or pathogen induced mortalities in Crassostrea spp. oysters populations from the known geographic distribution of P. beihaiensis.
b) None reported.
c) Perkinsus-like protists were observed in 3 of 14 Pinctada maxima examined histologically after 12 months of heavy mortalities following transplantation. However, the significance of the infections was unknown and the mortalities were attributed to adverse handling of the oysters prior to arrival on the farm (Norton et al. 1993).

Diagnostic techniques

Histology: a) Trophozoites (spherical, "signet-ring" cells, 2 to 8 µm in diameter) each with a single eccentric nucleus that typically contains a prominent nucleolus and a large eccentric vacuole (that may contain ane eosinophilic vacuoplast) occupying much of the cell volume. Proliferation is by schizogony of a 4 to 12 µm mother cell to yield clusters of sibling daughter cells (Moss et al. 2008a). Trophozoite morphology does not have taxonomic value because it can be influenced by the host, the time of the year, and nutrient availability (Villalba et al. 2004). Lesions usually associated with infection consist of many Perkinsus sp. surrounded by oyster haemocytes (mainly nongranulocytic) and some parasites occur within haemocytes. Moss et al. (2008a) found P. beihaiensis to occur with decreasing frequency among visceral connective tissues, stomach and intestinal epithelium, mantle and gill connective tissue and digestive gland epithelia.
b and c) Histological analysis showed the occurrence of typical "signet-ring" trophozoites (3 to 7 µm in diameter) and tomonts (schizonts, 4 to 6 µm in diameter) infecting connective tissues of several organs (mainly the connective tissue of the mantle, gills and adjacent to the digestive tract) and digestive epithelia (Norton et al. 1993, Sabry et al. 2009).

DNA Probes: a) Analysis of nucleotide sequences of the small subunit (SSU) ribosomal RNA (rRNA) internal transcribed spacer (ITS) region and of the large subunit (LSU) rRNA and actin (type 1) genes, consistently from monophyletic clades that confirmed genus affiliation to species of Perkinsus but distinguished P. beihaiensis from all six accepted species of Perkinsus described prior to 2008 (Moss et al. 2008a). These sequences were deposited with GenBank (http://www.ncbi.nlm.nih.gov/Genbank). A polymerase chain reaction (PCR) assay was developed and optimized to detect P. beihaiensis but not other species of Perkinsus, related protists and other pathogens of oysters (Moss et al. 2008a). Also, a P. beihaiensis-specific in situ DNA probe hybridization assay was designed to target the LSU rRNA of P. beihaiensis in histological section of infected oysters (Moss et al. 2008a).
b) PCR and restriction fragment length polymorphism (RFLP) assays specific to the genus Perkinsus, followed by cloning and sequencing of the internal transcribed spacer (ITS) region of the ribosomal ribonucleic acid (rRNA) gene complex, identified a close phylogenetic relationship between Brazilian Perkinsus sp. and P. beihaiensis infecting Chinese oysters (Sabry et al. 2009).

Culture: a) After incubation of tissues (usually rectal, gill and/or mantle tissues) in supplemented fluid thioglycollate medium (RFTM) for 5 to 7 days followed by staining with Lugol's iodine stain as described by Ray (1966) or using alternative Ray's fluid thioglycolate medium (ARFTM) as described by La Peyre et al. (2003), blue-black prezoosporangia (hypnospores 5 to 55 µm in diameter) were evident in infected oysters (Moss et al. 2008a). Although not true propagating cultures, this procedure is used for the diagnosis of many species of Perkinsus but may also detect other organisms (Villalba et al. 2004). Transfer of enlarged prezoosporangia of P. beihaiensis from ARFTM to nutrient medium resulted in zoosporulation of some cells. Zoosporangia (35 to 63 µm in diameter) had single polar discharge pores and tubes , and developed motile zoospores (3 to 5 µm long). However, the zoospores remained contained in the thick walled zoosporangia and further proliferation was not achieved even though the nutrient medium had the same formulation as the medium used for the in vitro culture of other species of Perkinsus (Moss et al. 2008a).
b)  Prezoosporangia of Perkinsus sp. from  C. rhizophorae in Brazil after incubation in RFTM and transfer to filtered seawater developed into zoosporangia which released numerous motile zoospores (2 µm long) after 48 to 96 hours (Sabry et al. 2009).

Methods of control

No known method of prevention or control.

References

Goggin, C.L. and R.J.G. Lester. 1987. Occurrence of Perkinsus species (Protozoa, Apicomplexa) in bivalves from the Great Barrier Reef. Diseases of Aquatic Organisms 3: 113-117.

La Peyre, M.K., A.D. Nickens, A.K. Volety, G.S. Tolley and J.F. La Peyer. 2003. Environmental significance of freshets in reducing Perkinsus marinus infection in eastern oysters Crassostrea virginica: potential management applications. Marine Ecology Progress Series 248: 165-176.

Moss, J.A., E.M. Burreson, J.F. Cordes, C.F. Dungan, G.D. Brown, A. Wang, X. Wu and K.S. Reece. 2007. Pathogens in Crassostrea ariakensis and other Asian oyster species: implications for non-native oyster introduction to Chesapeake Bay. Diseases of Aquatic Organisms 77: 207-223.

Moss, J.A., J. Xiao, C.F. Dungan and K.S. Reece. 2008a. Description of Perkinsus beihaiensis n. sp., a new Perkinsus sp. parasite in oysters of southern China. Journal of Eukaryotic Microbiology 55: 117-130.

Moss, J.A., C.F. Dungan and K.S. Reece. 2008b. Susceptibility of Chesapeake Bay bivalves to non-native Perkinsus species: pathogen risk associated with the introduction of Crassostrea ariakensis. Journal of Shellfish Research 27: 1034. (Abstract).

Norton, J.H., M.A. Shepherd, F.P. Perkins and H.C. Prior. 1993. Perkinsus-like infection in farmed golden-lipped pearl oyster Pinctada maxima from the Torres Strait, Australia. Journal of Invertebrate Pathology 62: 105-106.

Ray, S.M. 1966. A review of the culture method for detecting Dermocystidium marinum, with suggested modifications and precautions. Proceedings of the National Shellfisheries Association 54: 55-69.

Sabry, R.C., R.D. Rosa, A.R.M. Magalhães, M.A. Barracco, T.C.V. Gesteira and P.M. da Silva. 2009. First report of Perkinsus sp. infecting mangrove oysters Crassostrea rhizophorae from the Brazilian coast. Diseases of Aquatic Organisms 88: 13–23.

Villalba, A., K.S. Reece, M.C. Ordás, S.M. Casas and A. Figueras. 2004. Perkinsosis in molluscs: A review. Aquatic Living Resources 17: 411-432.

Citation Information

Bower, S.M.  (2010): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Perkinsus sp. of oysters in the Pacific and southern oceans.

URL: http://www.pac.dfo-mpo.gc.ca/science/species-especes/shellfish-coquillages/diseases-maladies/pages/perkinasoy-eng.htm

Date last revised:  November 2010
Comments to Susan Bower