Sheep mortality associated with paralytic shellfish poisons from the cyanobacterium Anabaena circinalis

This is the first report of sheep mortalities associated with paralytic shellfish poisons (PSPs) from the cyanobacterium Anabaena circinalis Rabenhorst. Fourteen sheep died within 150 m of a farm dam containing a dense bloom of A. circinalis. Extracts from both the cyanobacterium and small intestine from a dead ewe were analysed by high-performance liquid chromtography (HPLC) and found to contain PSPs. The toxin profiles of the cyanobacterium contained a high proportion of C-toxins (70%), whereas toxins in the small intestine content were dominated by gonyautoxin 5 (87%). This observation could be explained by desulfation of the C-toxins in the gut of the sheep. The LD100 of bloom material calculated from HPLC data was consistent with mouse bioassay data (12-25 mg/kg). The symptoms of affected sheep, mouse bioassay data, coupled with HPLC analysis of toxins from the bloom samples and the intestine contents, and the absence of other cyanobacterial alkaloid toxins, indicate that PSPs were responsible for the deaths of the sheep.