Clinical and Pathological Findings in Coastal Birds Affected by Domoic Acid Toxicity

In 2017, an unusually large number of live stranded and dead marine birds were found in California, coincident with a large bloom of the diatom Pseudo-nitzschia that produced the toxin domoic acid (DA). The most abundant bird species affected by this large die-off and stranding event were Pacific Loons (Gavia pacifica) and Red-throated Loons (Gavia stellata). International Bird Rescue (IBR; San Pedro, CA) received 117 live loons with suspected DA toxicosis. Many birds that survived the first few days in rehabilitation quickly re-attained suitable health metrics; however, 68 loons (58.1%) died or were considered unreleasable due to ongoing abnormal behavior or injuries that necessitated humane euthanasia. In this descriptive study, both live stranded euthanized birds and dead stranded birds were examined to characterize and better understand the effects of DA toxicosis in the avian brain and body. Utilizing a suite of diagnostics, our analysis revealed novel pathological patterns that divided these birds into three groups: those suspected of having acute, subacute, and chronic DA toxicosis. Domoic Acid was found in all groups, and the severity of the microscopic lesions appeared to correspond with the amount of time each bird survived post-stranding. Our investigation is the first known account identifying the pathological progression from acute to chronic DA toxicosis in birds.