Blister Disease of Cultured Abalone

Category

Category 3 (Host Not in Canada)

Common, generally accepted names of the organism or disease agent

Blister disease or pustule disease of cultured abalone.

Scientific name or taxonomic affiliation

Vibrio fluvialis II and possibly other bacteria (Nie and Wang 2004).

Geographic distribution

Disease is known to occur only in the Dalian area of China. However, V. fluvialis is present in aquatic, particularly estuarine, environments throughout the world (Lee et al. 1981).

Host species

Haliotis discus hannai.

Impact on the host

Blister-like lesions on the foot of various growth stages of cultured abalone were associated with mortalities as high as 50 to 60 % in at least three abalone culture facilities in the vicinity of Dalian, China. Vibrio fluvialis II cultured from the lesions caused identical signs of the disease in 100% of the experimental abalone exposed by inoculation.

Diagnostic techniques

Gross Observations: Blister-like lesions on the abalone foot.

Histology: The connective tissue and muscle fibers were dissolved and denatured by an intense inflammatory response in the centers of the lesions. The lesions first formed on the surface of the abalone foot and tended to migrate into the tissue as the disease progressed. In advanced stages of the disease, only haemocytes and V. fluvialis II remained in the center of the lesions.

Smears: Gram-negative, short rod-shaped bacterium were abundant in Gram stained smears of well developed lesions.

Electron Microscopy: Host cells within the lesions had evidence of nuclear membrane disintegration resulting in nucleoplasma diffusion, loss of the nucleolus and glycogenesome, and mitochondria denaturation. The short rod-shaped bacterium had a thin cellular wall, clear central zone with many glycogenosomes and free ribosomes in the plasma and a single polar flagellum.

Culture: The bacteria were cultured in 1% tryptone agar medium (with or without beef broth) made up with 20-30 parts per thousand seawater, pH of 5.5 to 11 and temperatures of 15 to 42 °C. Characteristics of the cultured forms include: fermentation of glucose with the production of gas, reduction of nitrate to nitrite, a positive Voges-proskauer test, hydrolization of arginine but not amylum nor gelatin, fermentation of arabinose but not xylose nor inositol, oxidase and catalase positive, and sensitivity to vibriostatic agent 0/129 (150 µg).

Methods of control

No known methods of prevention or control although, various antibiotics have been applied with some success (Nie and Wang 2004). Three strains of V. fluvialis II that were isolated from diseased abalone had varying resistance to 18 different antibiotics. The mechanism of drug resistance was related to gene mutations in the bacterium (Li et al. 1996b). Experimental results suggest that exposing abalone (via oral ingestion or injection) to a formalin treated culture of V. fluvialis-II improved the survival of cultured juvenile and adult abalone, and the serum of inoculated abalone had a higher agglutinin titre against the bacterium. The phage isolated from V. fluvialis II cultures and inoculated into the muscle of the foot and pustules on abalone increased abalone survival rate by up to 50% (Tai-wu et al. 2000).

Although the aetiological agent of pustule disease (V. fluvialis) is present in aquatic, particularly estuarine, environments throughout the world (Lee et al. 1981), the disease has only been reported in China. Perhaps the conditions in the abalone culture facilities in China may have predisposed the abalone to infection. Nevertheless, the possibility of the existence of a strain modified for pathogenicity to abalone can not be discounted. Thus, to avoid the risk of introducing this pathogen to other culture facilities or natural stocks, only animals certified to be free of infection should be considered for transplantation from areas where the disease occurs. In addition, imported animals must be held in quarantine and assayed for cryptic or subclinical infections prior to release into the new environment.

References

Bower, S.M. 2000. Infectious diseases of abalone (Haliotis spp.) and risks associated with transplantation. In: Campbell, A. (Editor), Workshop on Rebuilding Abalone Stocks in British Columbia. Canadian Special Publication of Fisheries and Aquatic Sciences 130:. In press.

Lee, J.V., P. Shread, A.L. Furniss and T.N. Bryant. 1981. Taxonomy and description of Vibrio fluvialis sp. nov. (synonym Group F vibrios, Group EF6). Journal of Applied Bacteriology 50: 73-94.

Li, T.-W., J. Xiang and R. Liu. 1996a. Comprehensive studies and control of disease of cultured abalone Haliotis discus hannai. Various unpublished abstracts, for copies contact S.M. Bower.

Li, T.-W., M. Ding, X. Song, J. Xiang and R. Liu. 1996b. Preliminary studies on the mechanism of Vibrio fluvialis II resistance to antibiotics. Oceanologia et Limnologia Sinica 27: 637-645. (In Chinese with English abstract).

Li, T.-W., M. Ding, J. Xiang and R. Liu. 1997a. Immunological studies on Haliotis discus hannai with Vibrio fluvialia II. Oceanologia et Limnologia Sinica 28: 27-32. (In Chinese with English abstract).

Li, T.-W., J. Zhang, M.-J. Ding, S.-J. Wang, P. Shi, J.-H. Xiang and R.-Y. Liu. 1997b. Histology and ultrastructure of pustule disease in abalone Haliotis discus hannai (Mollusca: Gastropoda). Acta Zoologica Sinica 43: 238-242.

Li, T.-W., M. Ding, J. Zhang, J. Xiang and R. Liu. 1998. Studies on the pustule disease of abalone (Haliotis discus hannai Ino) on the Dalian coast. Journal of Shellfish Research 17: 707-711.

Liu, J., L. Nie, T. Li, M. Ding, X. Song and R. Zhao. 1995. A study on pustule disease of Haliotis discus. Journal of Fishery Sciences of China 2: 78-84. (In Chinese with English abstract).

Nie, Z. and S. Wang. 2004. The status of abalone culture in China. Journal of Shellfish Research 23: 941-945.

Nie, L., J. Liu and T. Li. 1995. Physiological and biochemical characteristics of the pathogen of pustule disease of H. discus. Chinese Journal of Microecology 7: 33-36. (In Chinese with English abstract).

Tai-wu, L. (same author as Li, T.-W.), J. Xiang and R. Liu. 2000. Studies on phage control of pustule disease in abalone Haliotis discus hannai. Journal of Shellfish Research 19: 535. (Abstract).

Citation Information

Bower, S.M., Li Tai wu (2007): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Blister Disease of Cultured Abalone.

Date last revised: November 2007
Comments to Susan Bower

Date modified: