Abstract
A major epizootic of West Indian manatees occurred in early 1996 on Florida's Gulf of Mexico. By early May more than 150 animals had died. An unusual temporal distribution of manatees and Florida red tide, combined with cold weather, exposed animals to very high concentrations of the causative organism Gymnodinium breve. A very similar event occurred in 1973, when 37 animals succumbed to red tide poisoning. The causative agents, the polyether brevetoxins (PbTx), were demonstrated by synaptosome binding assay at 50 to 100-fold above background in tissue samples of lung, buccal membranes, liver, kidney, and in stomach contents. Histological staining, using a brevetoxin immunoperoxidase detection method, demonstrated toxin accumulation in phagocytic cells of brain, spleen, liver, and kidney. Duplicate manatee tissues stained for a major apoptosis enzyme, interleukin converting enzyme I (ICE I), further revealed that cells that had accumulated brevetoxin were programmed for cell death. Tissues from PbTx-exposed mice stained in an identical manner, indicated accumulation of toxin in lymphocytes. Brevetoxin incubated in vitro with cathepsin B,H, and L, the major proteolytic enzymes in phagocytic cells, inhibited the enzymes in a specific dose-dependent manner. The implications of chronic polyether marine intoxication will be presented.