Perkinsus spp. of Oysters in the North Pacific and Southern Oceans


Category 1 (Not Reported in Canada)

Common, generally accepted names of the organism or disease agent

Perkinsus spp. of oysters in the North Pacific and southern oceans.

Scientific name or taxonomic affiliation

The specific identity of some of these parasites has not yet been fully confirmed. Reports pertaining to the same parasites were assigned a letter code which is consistently applied to all available information on those parasites under each of the following headings.

  1. Perkinsus beihaiensis (Moss et al. 2008a).
  2. Perkinsus sp. with genetic similarities to P. beihaiensis (Sabry et al. 2009). Further phylogenetic analyses by Sabry et al. (2013) strongly indicate that this parasite belonged to Perkinsus beihaiensis. Nevertheless, this parasite is referred to as "the Brazilian P. beihaiensis" in the following text. This parasite, other unidentified Perkinsus spp. and/or Perkinsus marinus were also reported from Brazil (da Silva et al. 2012, Brandão et al. 2013, Queiroga et al. 2013, Sabry et al. 2013). The presence of P. marinus was confirmed by da Silva et al. (2013) using phylogenetic analyses.
  3. Perkinsus-like protist (Norton et al. 1993).
  4. Perkinsus sp. (Taveekijakarn et al. 2008).
  5. Perkinsus olseni was identified by molecular analysis from Pinctada fucata (Sanil et al. 2010) and Perkinsus beihaiensis and "the Brazilian P. beihaiensis" were identified by molecular analysis from Crassostrea madrasensis (Sanil et al. 2012). The Perkinsus marinus detected in tissues of C. madrasensis assayed by the non-specific fluid thioglycollate medium - RFTM diagnostic procedure and reported by Muthiah and Nayara (1988) was considered to be a case of misidentification (Sanil et al. 2010, 2012).

Geographic distribution

  1. 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).
  2. Initially reported from the Pacoti River estuary in Ceará State, northeast Brazil (Sabry et al. 2009, 2013), "the Brazilian P. beihaiensis" and other unidentified Perkinsus spp. were detected in the Paraíba and Mamanguape river estuaries, Paraíba State, northeast Brazil (da Silva et al. 2012, Queiroga et al. 2013). Perkinsus marinus was confirmed to occur in the Paraíba River estuary (da Silva et al. 2013). Also, unidentified species of Perkinsus were reported from the coast of Bahia State, Brazil (Brandão et al. 2013).
  3. 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).

    d) Bangplasoy in Chonburi Province, Thailand at the upper part of the Gulf of Thailand (Taveekijakarn et al. 2008).

  4. Bangplasoy in Chonburi Province, Thailand at the upper part of the Gulf of Thailand (Taveekijakarn et al. 2008).
  5. Perkinsus olseni and P. beihaiensis were reported from several locations along the Gulf of Mannar, southeast coast of India (Sanil et al. 2010, 2012) and "the Brazilian P. beihaiensis" was detected in this area as well as on the southwest coast of India (Sanil et al. 2012).

Host species

  1. 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).
  2. Crassostrea rhizophorae (Sabry et al. 2009, 2013; da Silva et al. 2012, 2013; Brandão et al. 2013). Unidentified species of Perkinsus were also reported from Crassostrea gasar (=brasiliana) (da Silva et al. 2012, Queiroga et al. 2013).
  3. 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).
  4. Saccostrea forskali detected by histology in only one of 150 oysters that were over one year of age and sampled in November 2004 (Taveekijakarn et al. 2008).
  5. Crassostrea madrasensis (Muthiah and Nayara 1988, Sanil et al. 2012) and in wild and farmed Pinctada fucata (Sanil et al. 2010).

Impact on the host

  1. Perkinsus beihaiensis was initially detected in Asian oysters being examined 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.
  2. The impact of Perkinsus spp. on oyster populations in Brazil has not been assessed. Although a 81.5% mean prevalence of perkinsosis was reported by da Silva et al. (2013) in C. rhizophorae from northeast Brazil, associated pathology was not evaluated. Brandão et al. (2013) also reported a high prevalence of infection (between 87 and 92% at one location) in C. rhizophorae on the coast of Bahia State with insignificant evidence of histopathology and no apparent compromise on the health of the oysters. However, Queiroga et al. (2013) observed an increase in haemocyte mortality, a suppression of phagocytosis and Reactive Oxygen Species production, and possibly an induction of haemocyte proliferation in heavily infected C. gasar from the Mamanguape River estuary, Paraíba State with no evidence of associated mortality.
  3. 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).
  4. Variously-sized trophozoites and tomonts were scattered in necrotic areas of the gonad and among the connective tissue between degenerated tubules of digestive gland. Most of the parasites were tomonts but some typical "signet ring" trophozoites were also observed (Taveekijakarn et al. 2008).
  5. No mortality could be decisively attributed to Perkinsus spp. in oyster populations in India (Muthiah and Nayara 1988). In Crassostrea madrasensis, the percentage of infected oysters varied from a low of 10% during February to a high of 60% in May 1985 (Muthiah and Nayara 1988). Sanil et al. (2012) also found no mortality nor macroscopic clinical signs nor pathology associated with Perkinsus infections in C. madrasensis. However, Sanil et al. (2010) suggested that perkinsosis could be one of the major reasons for the decline of P. fucata populations in the Gulf of Mannar. Apparently, P. fucata collected from the wild had a higher intensity of infection when compared to those reared in the hatchery (Sanil et al. 2010).

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 (tomont) 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, c, d and e) Histological analysis showed the occurrence of typical "signet-ring" trophozoites (3 to 8 µm in diameter) and tomonts (schizonts, 3 to 8 µm in diameter) infecting connective tissues of several organs (mainly the connective tissue of the mantle, gills, muscle, gonad and adjacent to the digestive tract) and digestive epithelia (Norton et al. 1993, Taveekijakarn et al. 2008, Sabry et al. 2009, Sanil et al. 2012. Brandão et al. 2013). Although Sanil et al. (2010) observed protozoa measuring 4.7 to 7.3 µm in diameter in the tissues of infected pearl oysters (Pinctada fucata), no typical "signet-ring" trophozoites were found in the histological preparations studied.

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 ( 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 "the Brazilian P. beihaiensis" and P. beihaiensis infecting Chinese oysters (Sabry et al. 2009). Further phylogenetic analysis of ITS sequences of other isolates of this parasite and equivalent sequences available in GenBank lead Sabry et al. (2013) to conclude that this parasite was P. beihaiensis. Similar procedures were used by da Silva et al. (2013) to identify the Perkinsus grown in vitro from eight infected C. rhizophorae as P. marinus.

c and d) No information.

e) Screening of the tissues from pearl oysters (P. fucata) using the Perkinsus genus specific primers followed by sequencing the amplified PCR products showed 99% identity to Perkinsus olseni. The pairwise genetic distance values and phylogenetic analysis also confirm that the isolate from P. fucata was a member of the P. olseni clade (Sanil et al. 2010). The taxonomic affinities of the six Perkinsus isolates from C. madrasensis were determined to be P. beihaiensis (two isolates) and "the Brazilian P. beihaiensis" clade (four isolates) based on the transcribed spacer (ITS) sequences (98 to 100% identity) using basic local alignment search tool (BLAST) analysis. The pairwise genetic distance values and phylogenetic analysis confirmed these results (Sanil et al. 2013). Sanil et al. (2013) proposed that the genetic divergence data, close affinity with "the Brazilian P. beihaiensis", and co-existence with P. beihaiensis in the same host species in the same habitat possibly indicated intraspecific variants of P. beihaiensis having a separate lineage in the process of evolution. The sequencing of actin genes did not show any divergence among the samples studied (Sanil et al. 2013).

Culture: Although not true propagating cultures, the assay commonly known as RFTM is often used to detect Perkinsus spp. RFTM is carried out by incubating tissues (usually rectal, gill and/or mantle tissues) in supplemented fluid thioglycollate medium (FTM) plus antibiotics for 5 to 7 days followed by staining with Lugol's iodine stain as described by Ray (1966). An alternative Ray's fluid thioglycolate medium (ARFTM) assay was described by La Peyre et al. (2003). Positive results from both assays are blue-black prezoosporangia (hypnospores 5 to 55 µm in diameter) in tissues from infected oysters (Moss et al. 2008a). However, this procedure is not specific and may also reveal other organisms that are not species of Perkinsus (Villalba et al. 2004).

a) The 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 a single polar discharge pore and tube, 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) RFTM is frequently used in Brazil to detect and evaluate the intensity of infection of Perkinsus spp. (Sabry et al. 2009, 2013; da Silva et al. 2013; Brandão et al. 2013; Queiroga et al. 2013). Prezoosporangia of Perkinsus sp. from C. rhizophorae 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). Gill tissue from infected C. rhizophorae was used by da Silva et al. (2013) to propagate trophozoite of P. marinus, some of which developed into zoosporangia that released zoospores into the nutrient medium.

c and d) No information.

e) Typical blue-black prezoosporangia were detected in the mantle and rectal tissue of oysters assayed by RFTM (Muthiah and Nayara 1988, Sanil et al. 2010, 2013).

Methods of control

No known method of prevention or control.


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Citation Information

Bower, S.M. (2013): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Perkinsus spp. of oysters in the North Pacific and southern oceans.

Date last revised: December 2013
Comments to Susan Bower

Date modified: