Vibrio spp. (Larval and Juvenile Vibriosis) of Clams

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• Category
• Common, generally accepted names of the organism or disease agent
• Scientific name or taxonomic affiliation
• Geographic distribution
• Host species
• Impact on the host
• Diagnostic techniques
• Methods of control
• References
• Citation information

Category

Category 4 (Negligible Regulatory Significance in Canada)

Common, generally accepted names of the organism or disease agent

1. Larval Vibriosis, Bacillary necrosis, Vibrio of Tapes philippinarum,VTP.
2. Juvenile Vibriosis, Bacillary necrosis.

Scientific name or taxonomic affiliation

1. Vibrio anguillarum, Vibrio alginolyticus, Vibrio tubiashii, Vibrio splendidus (specifically V. splendidus biovar II), and Vibrio sp. Sutton and Garrick (1993) reported bacteria with phenotypic characteristics 80% or greater similar to Vibrio orientalis, Vibrio campbelli, Vibrio metschnikovii, Vibrio harveyi and Photobacterium (Vibrio) damsela as pathogenic to larval Tridacna gigas from a research hatchery in Australia.
2. Surface coating Vibrio sp. (possibly Vibrio alginolyticus).

Geographic distribution

In all marine waters where bivalve hatchery culture is practised. It is generally a problem only in the warmest months.

Host species

1. Mercenaria mercenaria, Venerupis (=Tapes, =Ruditapes) philippinarum,Ruditapes decussatus, Panope abrupta, Tridacna gigas and other cultured bivalve larvae and juveniles (spat) including oysters, scallops and abalone. However, some species of bivalves may be more resistant to the pathogenic effects of these bacteria than other species (Elston et al. 2008). Nicolas et al. (1992) indicated that VTP (Vibrio of Venerupis (=Tapes) philippinarum, called V. tapesi by Paillard et al. (2004)) did not affect oyster (Crassostrea gigas) and scallop (Pecten maximus) larvae.
2. Mercenaria mercenaria.

Impact on the host

Systemic infection of the soft-tissues of the larvae, resulting in tissue necrosis (due to production of exotoxin by the bacteria) and death. Two episodes of mass mortality of cultured larvae and juveniles of Ruditapes decussatus associated with Vibrio spp. infections were recorded during 2001 and 2002 in a commercial hatchery located in Spain (Gómez-León et al. 2005). In general, adult bivalves do not suffer high mortalities when experimentally challenged with larval pathogens (Paillard et al. 2004).

Diagnostic techniques

Note: Definitive diagnosis of the disease as vibriosis or one resulting from other bacteria requires identification of the specific species or strain involved by appropriate biochemical, immunodiagnostic, or molecular methods. However, consistent isolation of numerically dominant bacteria (Gram negative rods) from tissues with characteristic lesions provides a strong presumptive diagnosis.

Wet mount

Symptoms of bacterial disease were usually rapid with profuse bacterial growth on and in larval clams and disintegration of most tissues within 48 hours. A pale color of the digestive tract in the affected larvae, possibly caused by a decrease in feeding activity, may occur. Moribund larvae are usually surrounded by swarming bacteria.

Histology

The presence of rod shaped bacteria (usually slightly curved) are associated mainly with the velum, mantle and connective tissue and indications of tissue necrosis are usually evident. Disease can also include disorganization of muscles fibres and strong haemocytic infiltration, especially in the connective tissue

Culture

Isolation and culture of colonies of Vibrio from the tissues of diseased clams. Examples of suitable culture media include TCBS bacterial culture agar or seawater-Trypticase-glucose-yeast (TGY) broth (composed of 0.4% Trypticase, 0.1% glucose, and 0.1% yeast extract) with the addition of 1.25% agar to make a solid medium. However, the Vibrio sp. called VTP from V. philippinarum does not grow on TCBS agar but can be grown on Zobell agar.

Molecular characteristics

Genomic analysis using polymerase chain reaction (PCR) and the nucleotide sequences of various genes (e.g., 16S ribosomal DNA (16S rDNA), rpoA, recA, and pyrH genes) are being employed to enable the differentiation between species of some Vibrio spp. (Paillard et al. 2004, Gómez-León et al. 2005, Thompson et al. 2005).

Methods of control

Vibrio bacteria are ubiquitous, hence eradication of the aetiologic agent is impossible. Vibriosis appears to be directly related to poor husbandry. Sources of infection are broodstock, algal cultures and incoming seawater. Determine the source of infection by culturing bacteria from these candidates. Batches containing infected individuals should be destroyed in an approved manner; disinfect all containers and equipment in contact with the infected stock. Elston et al. (2008) presented various techniques for the management and prevention of serious bacterial contamination in shellfish hatcheries.

Antimicrobial agents to reduce bacterial populations in and around the bivalve molluscs for the control and treatment of disease in mollusc hatcheries have been assessed and employed (Tubiash et al. 1965, Le Pennec and Prieur 1977, Gómez-León et al. 2005). However, the use of inhibitory compounds may lead to the rapid development of pathogen populations resistant to antibiotics, the elimination of beneficial organisms and the emergence of other microbial pathogens of the bivalves.

References

Elston, R.A., E.L. Elliot and R.R. Colwell. 1982. Conchiolin infection and surface coating Vibrio: shell fragility, growth depression and mortalities in cultured oysters and clams, Crassostrea virginica, Ostrea edulis and Mercenaria mercenaria. Journal of Fish Diseases 5: 265-284.

Elston, R.A., H. Hasegawa, K.L. Humphrey, I.K. Polyak and C.C. Häse. 2008. Re-emergence of Vibrio tubiashii in bivalve shellfish aquaculture: severity, environmental drivers, geographic extent and management. Diseases of Aquatic Organisms 82: 119–134.

Gómez-León, J., L. Villamil, M.L. Lemos, B. Novoa and A. Figueras. 2005. Isolation of Vibrio alginolyticus and Vibrio splendidus from aquacultured carpet shell clam (Ruditapes decussatus) larvae associated with mass mortalities. Applied and Environmental Microbiology 71: 98–104.

Hada, H.S., P.A. West, J.V. Lee, J. Stemmler and R.R. Colwell. 1984. Vibrio tubiashii sp. nov., a pathogen of bivalve molluscs. International Journal of Systematic Bacteriology 34: 1-4.

Kraeuter, J.N. and M. Castagna. 1984. Disease treatment in hard clams, Mercenaria mercenaria. Journal of the World Mariculture Society 15: 310-317.

Le Pennec, M. and D. Prieur. 1977. Les antibiotiques dans les elevages de larves de bivalves marins. (Antibiotics in larval rearing of marine bivalves) Aquaculture 12: 15-30. (In French, English abstract).

McGladdery, S.E. 1999. Shellfish diseases (viral, bacterial and fungal). In: Woo, P.T.K., D.W. Bruno (eds.) Fish Diseases and Disorders, Volume 3: Viral, Bacterial and Fungal Infections, Vol. 3. CABI Publishing, Wallingford, UK. pp. 723-842.

Mortensen, S., I. Arzul, L. Miossec, C. Paillard, S. Feist, G. Stentiford, T. Renault, D. Saulnier and A. Gregory. 2007. Molluscs and crustaceans, 5.3.6 Vibriosis caused by Vibrio spp. / V. splendidus-related strains. In: Raynard, R., T. Wahli, I. Vatsos, S. Mortensen (eds.) Review of disease interactions and pathogen exchange between farmed and wild finfish and shellfish in Europe. VESO on behalf of DIPNET, Oslo. pp. 334-340.

Nicolas, J.L., D. Ansquer and J.C. Cochard. 1992. Isolation and characterization of a pathogenic bacterium specific to Manila clam Tapes philippinarum larvae. Diseases of Aquatic Organisms 14: 153-159.

Paillard, C., F. Le Roux and J.J. Borrego. 2004. Bacterial disease in marine bivalves, a review of recent studies: Trends and evolution. Aquatic Living Resources 17: 477-498.

Plana, S. and M. LePennec. 1991. Alterations in the digestive diverticula and nutritional consequences in the clam Ruditapes philippinarum infected by Vibrio. Aquatic Living Resources 4:255-264. (In French).

Sutton, D.C. and R. Garrick. 1993. Bacterial disease of cultured giant clam Tridacna gigas larvae. Diseases of Aquatic Organisms 16: 47-53.

Thompson, F.L., D. Gevers, C.C. Thompson, P. Dawyndt, S. Naser, B. Hoste, C.B. Munn and J. Swings. 2005. Phylogeny and molecular identification of vibrios on the basis of multilocus sequence analysis. Applied and Environmental Microbiology 71: 5107–5115.

Tubiash, H.S., P.E. Chanley and E. Leifson. 1965. Bacillary necrosis, a disease of larval and juvenile mollusks. Journal of Bacteriology 90: 1036-1044.

Tubiash, H.S., R.R. Coldwell and R. Sakazaki. 1970. Marine vibrios associated with bacillary necrosis, a disease of larval and juvenile mollusks. Journal of Bacteriology 103: 271-272.

Citation Information

Bower, S.M. (2009): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Vibrio spp. (Larval and Juvenile Vibriosis) of Clams.

Date last revised: December 2009
Comments to Susan Bower