Sticky Polymers Spread Disease from Cats to Endangered Sea Otters

It seems that playful sea otters have a reason to fear domesticated cats. New research shows that certain sticky polymers produced by seaweed aids and abets the spread of disease from land animals to marine mammals.

According to the study, these large, complex molecules form slimy biofilms and bind water-borne organic matter into larger particles, to which disease-causing microorganisms can attach, thereby spreading disease to the marine food chain.

"Discovering the role that these invisible polymers play in disease transmission in the ocean is a tremendous step forward in helping us better understand and mitigate the impacts of coastal water pollution on the health of wildlife and humans," lead author Karen Shapiro, from the University of California, Davis, said in a statement.

Using the parasite Toxoplasma gondii as a model, Shapiro and her team showed how these sticky polymers increase the chance that disease-causing organisms would be picked up by marine snails, which graze on kelp and are among the common foods of some endangered sea otters.

Sea otters, which swim along the coasts of the Pacific Ocean in North America and Asia, were hunted for their fur to the point of near extinction. According to National Geographic, there are only 100,000 to 150,000 of these critters left, which are now protected by law.

Contamination of coastal waters is an obvious threat to the health of both humans and animals, but the mechanisms by which diseases are transmitted in marine ecosystems has until now remained a mystery.

The protozoan parasite T. gondii, which can also infect humans, actively reproduces in various cat species including domestic cats. It spreads via cat feces and can persist in the environment for months to years, infecting marine mammals including the endangered southern sea otter in California.

Researchers found that T. gondii infections were 10 times more common among sea otters that munched on kelp-grazing marine snails than among otters who ate other food. The reason? It turns out the gelatinous polymers, excreted by seaweed, act like a glue, helping to form sticky biofilms that can trap the T. gondii egg cells and coat kelp on which marine snails graze.

The findings were published in the journal Proceedings of the Royal Society B: Biological Sciences.