| Tracey Goldstein; School of Veterinary Medicine, UC Davis; tgoldstein@ucdavis.edu; Tanya Zabka, Gregg Langlois, Mary Silver, Linda J. Lowenstine, Frances M. Van Dolah, Joanna A.L. Mazet, Frances M. Gulland |
| The current unprecedented algal blooms off the California coast emphasize that domoic acid toxicosis is an increasing problem for marine vertebrates. Domoic acid is an excitatory neurotoxin produced by marine algae, such as Pseudo-nitzschia australis. Acute domoic acid toxicosis resulting from the glutamate agonist action of domoic acid was first documented in California sea lions (Zalophus californianus) that stranded off California in 1998. Animals displayed neurologic signs, including ataxia, disorientation, seizures, and death. Pathologic findings in acutely affected animals consisted of acute, ischemic, neuronal necrosis in the pyrimadal cells of the hippocampus and granular cells of the dendate gyrus, and acute myocardial necrosis. Since then, thousands of sea lions have stranded with signs of neurological disease at times when domoic acid producing plankton blooms were not always detected along the Pacific coast. Approximately 50% of these animals exhibit neurological effects longer than 2 weeks after initial stranding. Additionally, approximately 10% of affected sea lions re-strand following release, compared with 0.5% that re-strand following treatment for other reasons. Magnetic resonance imaging on live animals and histopathology from animals that died or were euthanized revealed varying degrees of unilateral and bilateral hippocampal atrophy, neuronal necrosis and gliosis in the limbic system. While all age classes and sexes are affected, 79% of cases have been adult females. Reproductive failure as a result of abortion and premature parturition was observed in approximately 1/3 of affected adult females. Domoic acid has been detected in amniotic fluid, fetal urine and gastric fluid tested up to 2 weeks after stranding. This suggests the fetus acts as a sink for domoic acid that is typically rapidly cleared from mammalian species (half life in primates is 4 hours). These data suggest that exposure to domoic acid can have effects on sea lion reproduction and survival beyond acute mortality documented to date and that animals may be exhibiting signs of persistent, sub-lethal exposure to the toxin. |