Bonamia perspora of Ostrea stentina

Category

Category 3 (Host Not in Canada)

Common, generally accepted names of the organism or disease agent

Microcell disease, Bonamiasis.

Scientific name or taxonomic affiliation

Bonamia perspora unlike other species of Bonamia (i.e., Bonamia ostreae, Bonamia exitiosa, Bonamia roughleyi and other unnamed species) produces spores similar to those of other spore-forming Haplosporidia. The Parsimony and Bayesian analyses of the small subunit ribosomal RNA (SSU rDNA) gene sequences conducted by Hill et al (2014), portrayed B. perspora and B. ostreae as sister species (though not well supported) separate from B. exitiosa and other Bonamia spp. that were assessed. This relationship was also found by the maximum parsimony analysis, minimum evolution methods, and the Parsimony bootstrap analysis of haplosporidian SSU rDNA sequences (Abollo et al. 2008, Engelsma et al. 2014). However, similar analyses (Parsimony and Bayesian) of the internal transcribed spacer region (ITS rDNA) of the same gene indicated that B. perspora formed a monophyletic clade separate from that of all other Bonamia spp. but the divergence of ITS rDNA sequences among species of Bonamia could make resolution of inter-specific relationships impossible using this locus (Hill et al. 2014).

Geographic distribution

Bogue Sound and Masonboro Sound, North Carolina, USA (Carnegie et al. 2006). Co-infections with B. exitiosa were detected in Wilmington, North Carolina, USA (Hill et al. 2014).

Host species

Ostrea stentina (=Osterola equestris).

Impact on the host

Overall low prevalence of 1.4% (31 oysters infective of 2,144 examined in 2004 and 2005) with the highest prevalence of 5.6% detected in June using polymerase chain reaction (PCR) detection methods (Carnegie et al. 2005, 2006). Infection intensity was not found at the very high intensities typical of infections by other Bonamia spp. Oysters containing B. perspora undergoing sporulation (spore formation) had sporogonic cell forms (sporonts, sporocysts and released spores) distributed throughout and sometimes completely filling the connective tissue of the oyster. Oysters with late sporulation stages displayed widespread disintegration of digestive diverticula with sporocysts and free spores occurring in the lumens of many digestive tubules. Haemocyte infiltration into infected tissue was generally strongest in infections dominated by uninucleate and diplokaryotic (binucleate) microcells and weakest in oysters with plasmodial infections or sporulation of B. perspora (Carnegie et al. 2006).

Diagnostic techniques

Histology: Bonamia perspora is remarkably larger (2 to 6 µm in diameter, with many greater than 5 µm in diameter) than other Bonamia spp. and it was rarely observed in haemocytes or other host cells. The uninucleate microcells were distributed throughout to connective tissues of infected oysters and were often abundant at the base of the epithelia of the gut and hemolymph sinuses. Plasmodia (multinucleate forms, up to 16 µm in diameter) were numerous and occurred within the connective tissue along with with sporonts and sporocysts (up to 26 µm). Spores (4.3 to 6.4 µm in length and 3-5 µm in width) were observed within degenerating sporocysts or free within the connective tissue and digestive tubules (Carnegie et al. 2006, Engelsma et al. 2014).

Electron microscopy: Uninucleate, diplokaryotic (binucleate stage with 2 apposed nuclei) and multinucleate plasmodial stages resemble those of other spore forming haplosporidians but few haplosporosomes (5 ± 3 per cell) were present and plasmodia were small (Carnegie et al. 2006). The uninucleate stages, including haplosporosome characteristics, of B. ostreae and B. perspora are more similar to each other than to other examined isolates of Bonamia spp. (Hine et al. 2014). Plasmodia develop into sporonts, sporoblasts, sporocysts and spores, as do Haplosporidium spp. and Minchinia spp. (Hine et al. 2014). Spores had a hinged opercular lid (2 to 3 µm in diameter), no episporoplasm and were ornamented. Ornamentations were wall derived ribbons (15 to 30 per spore, 1 to 3 µm long, 300 nm wide by 50 nm thick) that tapered in width but increased in thickness with distance from the spore wall and each ribbon had an apical four-pronged cap (Carnegie et al. 2006, Engelsma et al. 2014).

DNA Probes: A B. perspora SSU rDNA sequence was generated and the sequence analyzed by parsimony jackknife analysis to demonstrate inclusion in the monophyletic Bonamia clade with closer affiliation to B. ostreae than to B. exitiosa and the Bonamia sp. isolated from introduced Crassostrea ariakensis held in Bogue Sound, North Carolina (Carnegie et al. 2006). This sequence was used to identify B. perspora-specific primers applicable to PCR and fluorescent in situ hybridization (Carnegie et al. 2006).

Methods of control

To date there are no known eradication or control procedures. Until the method(s) of transmission and host specificity of B. perspora has been investigated, the movement of oysters out of endemic areas should be avoided.

References

Abollo, E., A. Ramilo, S.M. Casas, P. Comesaña, A. Cao, M.J. Carballal and A. Villalba. 2008. First detection of the protozoan parasite Bonamia exitiosa (Haplosporidia) infecting flat oyster Ostrea edulis grown in European waters. Aquaculture 274: 201–207.

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.

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.

Engelsma, M.Y., S.C. Culloty, S.A. Lynch, I. Arzul and R.B. Carnegie. 2014. Bonamia parasites: a rapidly changing perspective on a genus of important mollusc pathogens. Diseases of Aquatic Organisms 110: 5-23.

Hill, K.M., N.A. Stokes, S.C. Webb, P.M. Hine, M.A. Kroeck, J.D. Moore, M.S. Morley, K.S. Reece, E.M. Burreson and R.B. Carnegie. 2014. Phylogenetics of Bonamia parasites based on small subunit and internal transcribed spacer region ribosomal DNA sequence data. Diseases of Aquatic Organisms 110: 33-54.

Hine, P.M., R.B. Carnegie, M.A. Kroeck, A. Villalba, M.Y. Engelsma and B. EM. 2014. Ultrastructural comparison of Bonamia spp. (Haplosporidia) infecting ostreid oysters. Diseases of Aquatic Organisms 110: 55-63.

Citation Information

Bower, S.M. (2015): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Bonamia perspora of Ostrea stentina

Date last revised: April 2015
Comments to Susan Bower

Date modified: