The shocking effects of domoic acid in California sea lions

Algal blooms occur when large groups of algae (plant-like microorganisms) grow together in fresh or saltwater. As a whole, algal blooms are extremely beneficial, providing food for many different sea creatures. However, a small percentage of these organisms called Pseudo-nitzschia grow to a mass known colloquially as “Red Tide” or Harmful Algal Blooms (HABs) and release a marine biotoxin—domoic acid (DA)—the substance known for causing Amnesic Shellfish Poisoning (ASP).

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In mammals, acute DA exposure can cause heart failure and seizures while chronic exposure has been known to cause permanent brain damage. DA is not only found in the HABs, but also accumulates in small fish such as sardines, anchovies, and shellfish that are eaten by California sea lions and humans as well. For this reason, California sea lions act as food safety sentinels regarding the presence of HABs near California. Additionally, the findings associated with DA exposure in California sea lions demonstrate the potential health effects for other marine mammal species.

A retrospective study published in Frontiers in Veterinary Science¹ determines DA poisoning’s impact on the electroencephalograms (EEGs) of California sea lions using data taken over 7 years from 120 stranded patients.

The patients were divided into 2 groups: Neurologically Normaland Suspected DA Toxicosis. The normal group presented with various non-neurological issues such as abscesses, malnutrition, and entanglement, whereas the suspected DA group presented with neurological signs such as unresponsiveness, seizures, and ataxia. These researchers cored both groups’ EEG readings from 0 (no abnormal activity) to 3 (abundant, severely abnormal activity that often obliterates the background EEG).¹

In the Neurologically Normal group of California sea lions, only 6% received a score of 3, whereas 66% of sea lions in the suspected DA toxicosis group scored three.¹ All patients in the latter group displayed some form of epileptic-like activity in their EEG readings. The patients in the suspected DA group that received treatment with phenobarbital for these seizures did not experience any significant EEG changes upon following readings. It is unclear by what mechanism DA toxicosis induced this resistant behavior. However, treatment with benzodiazepines, midazolam, or lorazepam during EEG readings reduced the amount of slow wave discharges observed.

The researchers identified additional risk factors for EEG abnormalities secondary to DA toxicosis such as older age, female sex, and evidence of previous brain injury.¹

The current data is extremely limited due to the lack of available controls, follow ups, and loss of patients, however the data obtained was valuable to future endeavors using other animal models. Future research should evaluate patients with confirmed DA toxicosis to help determine this disorder’s functional aspects in relation to EEG abnormalities.

Ms Erlingheuser is a 2024 PharmD Candidate at the University of Connecticut.

Reference

Williams DC, Haulena M, Dennison S, et al. Pinniped electroencephalography: Methodology and findings in California sea lions (Zalophus californianus). Front Vet Sci. 2023;10:1040125. doi: 10.3389/fvets.2023.1040125