David J. Pasnik; Stephen A. Smith; Gerhard Schurig; Ramesh Vemulapalli
Aquatic Medicine Laboratory, Department of Biomedical Sciences and
Pathobiology, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic
Institute and State University, Blacksburg, VA
Mycobacteriosis is an economically important bacterial disease of
virtually all species of freshwater, brackish and marine fish (1). It is usually caused by
Mycobacterium marinum, M. fortuitum, or M. chelonae and is a chronic progressive
disease, leading to systemic infections and ultimately death. While the host's immune response
against aquatic Mycobacterium spp. Has been characterized (2,3), an effective vaccine
against mycobacteriosis has not been developed.
A vaccine for aquatic mycobacteriosis was created using a
Mycobacterium spp. 85A antigen and Brucella abortus as the delivery vector.
Previous studies in this laboratory have established that striped bass, Morone saxatilis,
are particularly susceptible to Mycobacterium spp (4). Therefore, juvenile striped bass
were used as a model to test the vaccine. Intraperitoneal vaccinations were administered on days
0, 14, and 35 with bacterial concentrations ranging from 106 through 1010
long with a sham-inoculated saline control group. On days 0, 14, 35, and 49, blood was drawn
from the caudal vessels of the fish for ELISA evaluation. Data from the ELISA exhibited a
significant humoral antibody response to the 85A antigen and B. abortus antigen among the
108, 109, and 1010 groups.
On day 49, fish were challenged with an intramuscular injection of M.
marinum at a concentration of 1.6 x 106 colony-forming units per fish. Moribund
fish were euthanized and routine histological examination performed to assess the protection
conferred by the vaccine. In addition, on day 56, the anterior kidney was harvested from a
sub-sample of each group of fish for a lymphoproliferative assay. This was used to assess the
cell-mediate immune response elicited by the vaccine.
The long-term goal of this project is to create a safe, effective,
marketable vaccine which will 1) decrease financial losses due to mycobacteriosis, 2) improve
the overall health and immuno-competence of economically-important cultured marine food fish, 3)
decrease antibiotic use in food fish, and 4) provide a protocol for developing fish vaccines
against other significant intracellular pathogens.
1. Austin, B. and D.A. Austin. 1993. Mycobacterium spp. In:
Austin, B. and D.A. Austin (eds) Bacterial Fish Pathogens" Disease in Farmed and Wild Fish.
Ellis Horwood, New York, N.Y.
2. Bartos, J.M. and C.V. Sommer. 1981. In vivo cell mediated
immune response to M. tuberculosis and M. salmoniphilum in rainbow trout (Salmo
gairdneri). Developmental and Comparative Immunology 5:75-83.
3. Chen, S.C., T. Yoshida, A. Adams, K.D. Thompson, and R.H.
Richards. 1996. Immune response of rainbow trout to extracellular products of Mycobacterium
spp. Journal of Aquatic Animal Health 8:216-222.
4. Wolf, J.C. and S.A. Smith. 1999. Comparative severity of
experimentally induced mycobacteriosis in striped bass Morone saxatilis and hybrid
tilapia Oreochromis spp. Diseases of Aquatic Organisms 38: 191-200.