Why Are California Sea Otters Dying?

September 16, 2019

The following is the story of a journey taken by a little parasite. Yes, parasites are yucky, but the routes they take can be fascinating for scientists, and in some cases, help resolve puzzles about death and disease.

Toxoplasma gondii is a parasite that affects warm-blooded animals such as rats, birds, and goats. But this parasite has a curious way of transforming, especially when it resides in a cat. When it makes its way into a cat’s gut, this parasite replicates, creating millions of oocysts that the cat eventually sheds in its feces (good riddance, right?). These parasites then travel along with the feces across different channels before ending up in city waterways and eventually flow into open waters like the ocean …

Judy Gallagher [CC BY 2.0 (https://creativecommons.org/licenses/by/2.0)]
That’s where our story begins. The Toxoplasma gondii parasite that ultimately winds up in a cat’s feces and into open waters has been linked to the deaths of California sea otters. What starts out as flu-like symptoms eventually become a brain infection that kills the sea otter.

Can humans help? As always, small steps go a long way. For now, scientists suggest that people throw their cat waste away in trash bags and into garbage bins instead of flushing it down the toilet since water treatment plants aren’t able to prevent these parasites from making their way into open waters. Furthermore, they suggest that cats be kept indoors, or that owners try and prevent their cats from killing rodents and birds—a place where these parasites like to hide.