THERAPEUTIC AND PROPHYLACTIC EFFECTS OF A PROTECTIVE MONOCLONAL-ANTIBODY (MAB-001) AGAINST THE PATHOGENIC HEMOFLAGELLATE CRYPTOBIA SALMOSITIC

We recently produced a species-specific monoclonal antibody (MAb-001) against a surface antigen of Cryptobia salmositica Katz 1951. When a s ingle dose (4 % body of weight in mi) of MAb-001 was injected into fis h infected with C. salmositica, subsequent parasitaemias were signific antly (p < 0.05) reduced at 48 h after treatment. Parasitaemias were s till significantly lower than in control fish (injected with cold-bloo ded vertebrate Ringer's solution, CBVR) 1 wk after injection of MAb-00 1. There was no significant difference in parasitaemias between inject ion of a single dose or a double dose of MAb-001. Injection of MAb-001 into fish before infection and at 1 wk after infection did not preven t infection. Parasitaemias in fish which received MAb on Days 0, 1, 2, 3, 4, 5, 6 (daily injected fish) were significantly higher than in fi sh which received CBVR. The production of complement-fixing antibody a gainst C. salmositica in MAb daily injected fish was significantly low er than in those injected with CBVR. Antibodies against MAb-001 were d etected in fish injected daily with MAb-001. These results suggest tha t a single dose of MAb-001 is therapeutic and perhaps can be used to p revent mortality of infected fish. Injection of MAb-001 every day in t he first week after infection induced significant antigenic competitio n between parasites and MAb-001. Consequently, these fish produced les s complement-fixing antibody against C. salmositica and this resulted in higher parasitaemias than in CBVR-injected fish.