Abstract

Domoic acid (DA) is a neuroexcitotoxin that bioaccumulates up the trophic levels of the food chain.⁵ Neuronal necrosis of the hippocampus along with lesions and gliosis in CA1, CA3, and CA4 zones of the cornu ammonis is associated with domoic acid toxicosis (DAT) in the California sea lion (Zalophus californianus).^2,7 DAT is divided into two syndromes: acute, characterized by ataxia, coma, and seizures and chronic, characterized by long-term epileptic activity in the absence of toxicity.⁴ Acute versus chronic syndromes are based on dose and length of exposure; however, animals with acute DAT may develop chronic DAT.³ Diagnosing these symptoms is important because they are treated differently. Differences in behavioral abnormalities between acute and chronic subjects were first described by Goldstein et al. (2008). A study conducted by Wittmaack et al. (in review) showed that behavioral diagnostic criteria had an 88% true positive rate and a 15% false positive rate. The study did not investigate differences between acute and chronic subjects. Using data from subjects identified as acute or chronic, (chronic n = 8, acute n = 20), we tested the hypothesis that subjects with chronic DAT (CDAT) would meet differing behavioral criteria than subjects with acute DAT (ADAT). Data were obtained at The Marine Mammal Center (TMMC) between 5/22/2011-8/25/2013 using focal animal continuous sampling with continuous recording methodology.^1,6 Diagnostic criteria included head weaving, a classic head weaving subtype, muscle fasciculations, a head muscle fasciculation subtype, dragging the hind flippers, and swift scanning. A head weaving severity score of 3, which indicated that head weaving was displayed consistently, was a part of the diagnostic criteria. Furthermore, four threshold levels were calculated, each with a differing likelihood of a false positive diagnosis. Results from the current study show that there were not any statistical differences between the CDAT and ADAT samples for head weaving (Wilcoxon p > 0.05), muscle fasciculations displayed at TMMC (Wilcoxon p > 0.05), dragging the hind flippers (Fisher's p > 0.05), swift scanning (Wilcoxon p > 0.05), classic head weaving (Wilcoxon p > 0.05), head muscle fasciculations (Wilcoxon p > 0.05), and a head weaving severity score of 3 (Fisher's p > 0.05). The display of muscle fasciculations on the beach, prior to rescue, was exclusive to the ADAT sample and displayed by 12% of subjects. Diagnostic threshold 3 was reached by a single subject in the CDAT sample. The similarity of behavioral criteria displayed is surprising given the differences between the two syndromes. Nonetheless, the exclusiveness of muscle fasciculations displayed on the beach by the ADAT sample provides the practitioner with an additional tool to help differentiate between ADAT and CDAT. Further research is required to test whether there is a relationship between diagnostic threshold 3 and CDAT.

Acknowledgements

I thank Denise Grieg, PhD, for her review of the abstract. Dr. Grieg had mentioned testing for differences between the subjects and I am grateful for her suggestion. I thank Dr. Frances Gulland for her continued guidance during the original project. I thank Dr. William Van Bonn for his advice and expertise during the original project. I thank Deb Wickham, Lauren Rust, Lorraine Barbosa DVM, and Sophie Guarasci for their assistance at TMMC. Finally, yet importantly, I thank the volunteers, Roger Connet, Mike Minton, Jake Trushiem, and Tracey Sonnoborn.

* Presenting author

Literature Cited

1.  Altmann J. Observational study of behavior: sampling methods. Behavior. 1974;49:227–265.

2.  Costa LG, Giordano G, Faustman EM. Domoic acid as a developmental neurotoxin. Neurotoxicology. 2010;31:409–423.

3.  Goldstein T, Mazet JAK, Zabka TS, et al. Novel symptomatology and changing epidemiology of domoic acid toxicosis in California sea lions (Zalophus californianus): an increasing risk to marine mammal health. Proceedings of the Royal Society of Biological Sciences. 2008;275:267–276.

4.  Gulland FM, Haulena M, Fauquier D, Lander ME, Zabka T, Duerr R, Langlois G. Domoic acid toxicity in Californian sea lions (Zalophus californianus): clinical signs, treatment and survival. Veterinary Record. 2002;150(15):475–480.

5.  Lefebere KA, Powell CL, Busman M, et al. Detection of domoic acid in northern anchovies and California sea lions associated with an unusual mortality event. Natural Toxins. 1999;7:85–92.

6.  Martin P, Batson P. Measuring Behavior: An Introductory Guide. New York, NY: Cambridge University Press; 2007: 186p.

7.  Silvagni PA, Lowenstine LJ, Spracker T, Lipscomb TP, Gulland FMD. Pathology of domoic acid toxicity in California sea lions (Zalophus californianus). Veterinary Pathology. 2005;42:184–191.