Submitted to: Journal of Fish Diseases
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/17/2001
Publication Date: 1/1/2002
Citation: SHELBY, R.A., KLESIUS, P.H., SHOEMAKER, C.A., EVANS, J.J. PASSIVE IMMUNIZATION OF TILAPIA (OREOCHROMIS NILOTICUS L.) WITH ANTI-STREPTCOCCUS INIAE WHOLE SERA. JOURNAL OF FISH DISEASES. 2002. 25, 1-6. Interpretive Summary: Streptococcal disease is caused by the bacterium Streptococcus iniae in man cultivated warm water fish species including tilapia. We conducted a series of experiments to measure the antibody response of tilapia to infection by this pathogen. We wanted to know how quickly and to what extent the animals responded to infection by producing antibodies. We were able to accomplish this using a newly developed assay method known as an ELISA test. We found that antibody levels in the surviving animals were measurably higher in infected animals after only 1 week, and remained elevated for 49 days, the duration of the experiment. When some of the surviving infected animals were re-infected with the same bacterium, antibody levels increased further and the fish had no additional symptons, suggesting a memory response which is similar to other species. Additionally, when serum from surviving fish was administered to uninfected fish, they also had fewer symptoms. These experiments show the protective effect of antibodies against Streptococcus iniae in this species.
Technical Abstract: Passive immunization of tilapia (Oreochromis niloticus) was conducted to determine whether anti-Streptococcus iniae whole sera (ASI) and normal whole sera (NWS) were protective when intraperitoneally (IP) injected into tilapia. The ASI was produced in tilapia actively immunized with virulent S. iniae by IP injection. An antibody response against S. iniae was demonstrated by ELISA and 18% of the immunized fish died due to the S. iniae infection. The actively immunized tilapia demonstrated an anamnestic antibody response and immunity to S. iniae after challenge with S. iniae by IP injection. Relative percent survival (RPS) was 100 in the actively immunized fish. The NWS was obtained from tilapia free of ASI antibody and susceptible to S. iniae infection (40% mortality). Mortalities in the tilapia passively immunized with ASI and NWS were 10% and 23%, respectively, after S. iniae infection by IP injection. A significantly higher RPS of 73.7 was noted in the fish passively immunized with the ASI, in comparison to a RPS of 39.5 in the fish passively immunized with the NWS. Disease signs were observed only in the tilapia immunized with NWS. The immunity provided by ASI was apparently due to antibody against S. iniae. The results of this study indicated a primary role of anti-S. iniae antibody in immunity against S. iniae.