Unidentified Species of Bonamia from Various Oysters and Locations


Category 3 (Host Not in Canada)

Common, generally accepted names of the organism or disease agent

Microcell disease, Bonamiasis, Haemocyte disease of oysters.

Scientific name or taxonomic affiliation

Bonamia spp. which resemble Bonamia ostreae a pathogen of European flat oysters Ostrea edulis, Bonamia roughleyi a pathogen of Sydney rock oysters Saccostrea glomerata, Bonamia exitiosa a pathogen of New Zealand dredge oysters Ostrea chilensis, and Bonamia perspora a parasite of the crested or horse oyster Ostreola equestris have been reported from various species of oysters in distant locations. The specific identity of these parasites has not yet been confirmed. However, Hall et al. (2010) suggested that Bonamia spp. isolates from Argentina, Australia, and the eastern USA have genetic affinities to the Bonamia exitiosa / Bonamia roughleyi clade. Each reported geographic location and host species was assigned a letter code which is consistently applied to all available information under each of the following headings.

Geographic distribution

  1. Western Australia, Victoria, New South Wales and Tasmania, Australia (pers. comm. Ben Diggles PhD, DigsFish Services, www.digsfish.com, ben@digsfish.com).
  2. Chiloe and Quihua Islands, Southern Chile (Kern 1993, Campalans et al. 2000, Lohrmann et al. 2009).
  3. San Antonio Bay and adjacent areas in San Matías Gulf, North Patagonia, Argentina (Kroeck and Montes 2005, Kroeck et al. 2008).
  4. Bogue and Masonboro Sounds, North Carolina, USA (Burreson et al. 2004, Carnegie et al. 2005, Wilbur et al. 2008), York River (Gloucester Point) and Chesapeake Bay, USA (Schott et al. 2008).
  5. Hawaii (Hill et al. 2008).

Host species

  1. Ostrea angasi.
  2. Ostrea (=Tiostrea) chilensis.
  3. Ostrea puelchana.
  4. Crassostrea ariakensis and Ostreola equestris. Infection was not detected in wild Crassostrea virginica from the same location as infected, experimentally introduced, C. ariakensis (Carnegie et al. 2006). However, Wilbur et al. (2008) detected Bonamia sp. DNA (via quantitative real-time PCR assay) in C. virginica from three estuaries in south eastern North Carolina with no detectable impact on the health of the positive oysters. This Bonamia sp. was detected in the same species, O. equestris, as Bonamia perspora (Carnegie et al. 2006).
  5. Ostrea sandvicensis.

Impact on the host

  1. Like B. ostreae and B. exitiosa, this intrahaemocytic protozoan quickly becomes systemic with overwhelming numbers of parasites coinciding with the death of the oyster. Preliminary unpublished reports from P.M. Hine (MAF New Zealand) indicate the Bonamia in O. angasi from Tasmania causes a different pathology by being epitheliotropic and associated with, but rare in, focal abscesses. However, Heasman et al. (2004) observed Bonamia sp. only in haemocytes and usually in areas of haemocytosis in O. angasi from New South Wales.
  2. Significance is unknown. Although high "levels" of infection were noted by Kern (1993) and prevalence up to 20% were detected by Arzul et al. (2005), no significant mortalities have been reported.
  3. This Bonamia sp. was associated with high mortalities (33% after 18 months, 80% after 31 months and 95% when the O. puelchana reached market size after 32 to 36 months of culture) and resulted in the termination of the culture effort (Kroeck and Montes 2005). Kroeck et al. (2008) propose that Bonamia sp. is an enzootic parasite of San Matías Gulf, because of its occurrence in native populations of O. puelchana from natural dense beds located close to the impacted oyster culture facilities. In the natural beds, there were no differences between the shell length of the parasitized and non-parasitized oysters and the probability of infection was independent of oyster sex (Kroeck et al. 2008).
  4. High prevalence of infection (up to 100%) were associated with high mortalities among triploid C. ariakensis in experimental field trials within a month of being transferred to grow-out locations in Bogue Sound, North Carolina in the summer of 2003. Cohorts at a distant location in North Carolina (Pamlico Sound) and in Chesapeake Bay, Virginia did not experience mortalities and were not infected with the Bonamia sp. (Burreson et al. 2004). However, Schott et al. (2008) reported a low prevalence of infection (2.7%) in triploid C. ariakensis experimentally reared near the mouth of the York River, Chesapeake Bay. Because C. ariakensisis not native to the east coast of the United States and was known to be free of infectious pathogens prior to the field trials, the source (natural host) for this Bonamia sp. is unknown. However, this Bonamia sp. was detected in low prevalence (3.3%) in O. equestrisfrom Bogue Sound, North Carolina in June 2003. Experimental results indicate that salinity below 30 parts per thousand were detrimental to Bonamia sp. in C. ariakensis (Audemard et al. 2005, 2008a) and warm temperature (greater than 20 °C) was associated with higher host mortality than colder temperatures, suggesting that temperature influenced Bonamia sp. pathogenicity (Audemard et al. 2008b). However, Bonamia sp. may be able to persist in C. ariakensis under a combination of low temperature and meso- to euhaline salinities (Audemard et al. 2008b). Also, Bonamia sp. activity was found to be seasonal with oyster mortality reaching 100% in late spring and summer deployments, early fall deployments showed reduced (17–82%) mortality and late fall and early winter deployments (made at temperatures less than 20 °C) did not develop Bonamia sp. infections (Carnegie et al. 2008). Crassostrea ariakensis can acquire infection with Bonamia sp. after 2 weeks of exposure in enzootic areas of North Carolina and laboratory studies suggest that this parasite can be directly transmitted between C. ariakensis in the laboratory (Audemard et al. 2008c).
  5. None reported.

Diagnostic techniques

Smear: Make acetone- (or methanol-) fixed impression smears from heart tissue (preferably ventricle since the auricles contain an abundance of serous cells which make detection of the parasite difficult). Stain with Wright, Wright-Giemsa or equivalent stain (e.g. Hemacolor, Merck; Diff-QuiK, Baxter). Examine for 2-5 µm spherical or ovoid organisms (microcells) with a central nucleus (fried egg appearance) within or outside the haemocytes. Note: The organisms are enlarged by this method compared to those in fresh or histological preparations.


  1. Examine haematoxylin and eosin stained tissue cross-sections for intracellular microcells (2-3 µm in diameter) within haemocytes. Bonamia are distributed systemically in advanced infections. In early infections, Bonamia are often observed within haemocytes in focal infiltrations in the connective tissue of the gill and mantle, and in the vascular sinuses around the stomach and intestine.
  2. Figure 1. Accumulation of haemocytes within the gills of Ostrea angasi infected with Bonamia sp. in Australia. Image provided by Ben Diggles PhD, DigsFish Services, www.digsfish.com, ben@digsfish.com.

    Figure 2.One Bonamia sp. (arrow) within a haemocyte among a group of haemocytes between vesicular connective tissue cells in a subclinical infection in Ostrea angasi. Image provided by Ben Diggles PhD, DigsFish Services, www.digsfish.com, ben@digsfish.com.

    Figure 3. A cluster of Bonamia sp.(arrows) in a haemocyte involved in an accumulation of haemocytes within the gills of a diseased Ostrea angasi. Image provided by Ben Diggles PhD, DigsFish Services, www.digsfish.com, ben@digsfish.com.

  3. Cells of Bonamia sp. were observed in connective tissue (free or within haemocytes) of the gills and around the digestive gland, stomach, intestine and gonad. Gross signs, histopathological alterations in O. puelchana, and Bonamia sp. cytological morphology resemble those reported for Bonamia exitiosa (Kroeck 2010).
  4. Lohrmann et al. (2009) examined the ultrastructure of the Chilean Bonamia sp. and reported that: 1) it resembles B. ostreae in size, the low number of mitochondrial profiles, and the prevalence and mean number of lipid droplets; 2) it differs from B. ostreae in the greater prevalence of nuclear membrane-bound Golgi (NM-BG), associated haplosporogenesis, and smaller size of haplosporosomes; 3) it resembles B. exitiosa in the number of haplosporosomes, prevalence of lipid droplets, anastomosing endoplasmic reticulum and NM-BG, presence of circles of smooth endoplasmic reticulum, and confronting and cylindrical cisternae; 4) it also appears to have a similar developmental cycle to B. exitiosa with larger forms occurring in winter (August). Based on similarities in ultrastructure and developmental stages between B. exitiosa and the Chilean Bonamia sp., Lohrmann et al. (2009) suggested that the 2 species are related, and that the Chilean Bonamia sp. is either B. exitiosa, a sub-species of B. exitiosa, or a separate species closely related to B. exitiosa.

DNA Probes:

  1. The sequences of the small subunit ribosomal DNA (SSU rDNA or 18S rDNA) is similar to that of Bonamia exitiosa but is only 64% homologous with that of Bonamia ostreae from Europe suggesting that this parasite may be conspecific with B. exitiosa and different from B. ostreae. Corbeil et al. (2006b) supported this suggestion by comparing the molecular sequence of the 18S-ITS-1 region of the small subunit rRNA operon obtained from 3 isolates from O. angasi collected from the Merimbula estuary in New South Wales, Australia with that of B. exitiosa and B. ostreae from the GenBank database. The Australian Bonamia sp. may derive from a common ancestor of B. exitiosa at the end of the Cretaceous, when New Zealand separated from Victoria, Australia or this parasite may have evolved in New Zealand and following mass mortalities of Australian oysters in the late 19th century was introduced to Australia with New Zealand oysters that were laid in Victorian and Tasmanian waters for the restaurant trade (Hine and Jones 1994). A real-time TaqMan PCR assay was developed for the detection of Bonamia spp. also detected the Bonamia sp. from O. angasi (Corbeil et al. 2006a).
  2. Partial sequences of the SSU (18S) and internal transcribed spacers (ITS) regions of the ribosomal DNA (rDNA) suggested that the parasite was closely related but distinct from B. ostreae and B. exitiosa (Arzul et al. 2005, White et al. 2008). A real-time TaqMan PCR assay was developed for the detection of Bonamia spp. also detected the Bonamia sp. from O. puelchana (Corbeil et al. 2006a).
  3. Based on genetic (parsimony) analysis, White et al. (2008) suggested that a single Bonamia species which resembles B. exitiosa may occur in New Zealand, Australia, Argentina and North Carolina. However, Kroeck (2010) proposed to treat the Argentinean species as B. exitiosa-like until more molecular and ultrastructural studies are conducted to determine the correct taxonomy.
  4. Two polymerase chain reaction (PCR) assays known to amplify the SSU rDNA of various species of Bonamia (Carnegie et al. 2000 and Cochennec et al. 2000) produced amplicons of the predicted size from all infected C. ariakensis that were assayed. Sequencing of the products yielded a single SSU rDNA sequence (GenBank Accession number AY542903) that was clearly a species of Bonamia but different from other Bonamia spp. (B. ostreae, B. exitiosa, and B. roughleyi) for which sequence data was available (Burreson et al. 2004). In situ hybridisation with Bonamia-specific probes reacted with the Bonamia sp. in C. ariakensis from Bogue Sound, North Carolina. Schott et al. (2008) reported novel Bonamia-related sequences as well as those closely related to previously described Bonamia spp. in C. ariakensis from Chesapeake Bay, USA (GenBank Accession number AY923853-AY923857).
  5. The Bonamia sp. detected by genus specific PCR and histological examination in Ostrea sandvicensis from Hawaii was found to be novel and basal to the rest of the Bonamia clade based on phylogenetic analysis of the SSU and ITS rDNA gene sequences (Hill et al. 2008).

Methods of control

To date there are no known eradication or control procedures. Until the method(s) of transmission and host specificity of these parasites has been investigated, the movement of oysters out of endemic areas should be avoided. Carnegie et al. (2008) determined that infection with Bonamia sp. in Crassostrea ariakensis in North Carolina was seasonal and influenced greatly by temperature. Thus, avoiding peak seasonal Bonamia sp. activity (late spring through early fall when water temperatures are greater than 20 °C) will be essential for culturing C. ariakensis in Bonamia sp.-enzootic waters (Carnegie et al. 2008).


Arzul, I., J.-P. Joly, M. Robert, B. Chollet, C. Garcia, L. Miossec, N. Cochennec, N. Carrasco, J. Campalans, M. Campalans and F. Berthe. 2005. Microcells in flat oysters, Ostrea chilensis from Chiloe Island, Chile: a new Bonamia species? Journal of Shellfish Research 24: 639. (Abstract).

Audemard, C., R. Carnegie, N. Stokes, E. Burreson and M. Bishop. 2005. Salinity effects on the susceptibility to and persistence of Bonamia ostreae and Bonamia sp. in Crassostrea ariakensis. Journal of Shellfish Research 24: 639. (Abstract).

Audemard, C., R.B. Carnegie, N.A. Stokes, M.J. Bishop, C.H. Peterson and E.M. Burreson. 2008a. Effects of salinity on Bonamia sp. survival in the Asian oyster Crassostrea ariakensis. Journal of Shellfish Research 27: 535-540.

Audemard, C., R.B. Carnegie, M.J. Bishop, C.H. Peterson and E.M. Burreson. 2008b. Interacting effects of temperature and salinity on Bonamia sp. parasitism in the Asian oyster Crassostrea ariakensis. Journal of Invertebrate Pathology 98: 344–350.

Audemard, C., R.B. Carnegie, K.M. Hill, C.H. Peterson and E.M. Burreson. 2008c. Investigation of Bonamia sp. transmission among, and incident in, Crassostrea ariakensis. Journal of Shellfish Research 27: 986. (Abstract).

Burreson, E.M., N.A. Stokes and R.B. Carnegie. 2004. Bonamia sp. (Haplosporidia) found in nonnative oysters Crassostrea ariakensis in Bogue Sound, North Carolina. Journal of Aquatic Animal Health 16: 1-9.

Campalans, M., P. Rojas and M. Gonzalez. 2000. Haemocytic parasitosis in the farmed oyster Tiostrea chilensis. Bulletin of the European Association of Fish Pathologists 20: 31-33.

Carnegie, R.B. and N. Cochennec-Laureau. 2004. Microcell parasites of oysters: recent insights and future trends. Aquatic Living Resources 17: 519-528.

Carnegie, R.B., B.J. Barber, S.C. Culloty, A.J. Figueras and D.L. Distel. 2000. Development of a PCR assay for detection of the oyster pathogen Bonamia ostreae and support for its inclusion in the Haplosporidia. Diseases of Aquatic Organisms 42: 199-206.

Carnegie, R.B., N.A. Stokes, C. Audemard and E.M. Burreson. 2005. Bonamiasis in the crested oyster Ostrea equestris in North Carolina, USA. Journal of Shellfish Research 24: 644. (Abstract).

Carnegie, R.B., E.M. Burreson, P.M. Hine, N.A. Stokes, C. Audemard, M.J. Bishop and C.H. Peterson. 2006. Bonamia perspora n. sp. (Haplosporidia), a parasite of the oyster Ostreola equestris, is the first Bonamia species known to produce spores. Journal of Eukaryotic Microbiology 53: 232-245.

Carnegie, R.B., N.A. Stokes, C. Audemard, M.J. Bishop, A.E. Wilbur, T.D. Alphin, M.H. Posey, C.H. Peterson and E.M. Burreson. 2008. Strong seasonality of Bonamia sp. infection and induced Crassostrea ariakensis mortality in Bogue and Masonboro Sounds, North Carolina, USA. Journal of Invertebrate Pathology 98: 335–343.

Cochennec, N., F. LeRoux, F. Berthe and A. Gerard. 2000. Detection of Bonamia ostreae based on small subunit ribosomal probe. Journal of Invertebrate Pathology 76: 26-32.

Corbeil, S., I. Arzul, B. Diggles, M. Heasman, B. Chollet, F.C.J. Berthe and M.S.J. Crane. 2006a. Development of a TaqMan PCR assay for the detection of Bonamia species. Diseases of Aquatic Organisms 71: 75-80.

Corbeil, S., I. Arzul, M. Robert, F.C.J. Berthe, N. Besnard-Cochennec and M.S.J. Crane. 2006b. Molecular characterisation of an Australian isolate of Bonamia exitiosa. Diseases of Aquatic Organisms 71: 82-85.

Heasman, M., B.K. Diggles, D. Hurwood, P. Mather, I. Pirozzi and S. Dworjanyn. 2004. Paving the way for continued rapid development of the flat (angasi) oyster (Ostrea angasi) farming industry in New South Wales. Final Report to the Department of Transport & Regional Services, Project No. NT002/0195 June 2004 NSW Fisheries Final Report Series No. 66. NSW Fisheries, Nelson Bay. (Link to publication: http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0003/134481/Output-448.pdf).

Hill, K.M., D.M. White, N.A. Stokes, R.B. Carnegie, N. Aloui-bejaoui, S.C. Webb, P.M. Hine, M.A. Kroeck, R. Ghars alli, R.K. Crockett, T.D. Lewis, K.S. Reece and E.M. Burreson. 2008. New perspectives on the dispersal and evolution of Bonamia species, haplosproidian parasites of oysters. Journal of Shellfish Research 27: 1016. (Abstract).

Hill, K.M., R.B. Carnegie, N. Aloui-Bejaoui, R.E. Gharsalli, D.M. White, N.A. Stokes and E.M. Burreson. 2010. Observation of a Bonamia sp. infecting the oyster Ostrea stentina in Tunisia, and a consideration of its phylogenetic affinities. Journal of Invertebrate Pathology 103: 179–185.

Hine, P.M. and J.B. Jones. 1994. Bonamia and other aquatic parasites of importance to New Zealand. New Zealand Journal of Zoology 21: 49-56.

Kern, F.G. 1993. Shellfish health inspections of Chilean and Australian oysters. Journal of Shellfish Research 12: 366. (Abstract).

Kroeck, M.A. 2010. Gross signs and histopathology of Ostrea puelchana infected by a Bonamia exitiosa-like parasite (Haplosporidia). Diseases of Aquatic Organisms 89: 229–236.

Kroeck, M.A. and J. Montes. 2005. Occurrence of the haemocyte parasite Bonamia sp. in flat oysters Ostrea puelchana farmed in San Antonio Bay (Argentina). Diseases of Aquatic Organisms 63: 231-235.

Kroeck, M.A., L. Semenas and E.M. Morsan. 2008. Epidemiological study of Bonamia sp. in the native flat oyster, Ostrea puelchana from San Matías Gulf (NW Patagonia, Argentina). Aquaculture 276: 5–13.

Lohrmann, K.B., P.M. Hine and M. Campalans. 2009. Ultrastructure of Bonamia sp. in Ostrea chilensis in Chile. Diseases of Aquatic Organisms 85: 199–208.

Schott, E.J., J.A. Fernández-Robledo, M.R. Alavi and G.R. Vasta. 2008. Susceptibility of Crassostrea ariakensis (Fujita 1913) to Bonamia and Perkinsus spp. infections: potential for disease transmission between oyster species. Journal of Shellfish Research 27: 541-549.

White, D., N. Stokes, K. Hill, M. Kroeck, P.M. Hine, N. Aloui-bejaoui, R. Carnegie, K. Reece and E. Burreson. 2008. A molecular phylogeny of the genus Bonamia based on internal transcribed spacer region sequences. Journal of Shellfish Research 27: 1063. (Abstract).

Wilbur, A.E., J.D. Gauthier, T.D. Alphin and M.H. Posey. 2008. Preliminary investigations into the occurrence of a novel parasite (Bonamia sp.) associated with the eastern oyster Crassostrea virginica. Journal of Shellfish Research 27: 1064. (Abstract).

Citation Information

Bower, S.M. (2011): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Unidentified Species of Bonamia from Various Oysters and Locations

Date last revised: May 2011
Comments to Susan Bower

Date modified: