Microplastics Can Transport Parasites to Oceans, Impacting Wildlife and Humans

Microplastics are a pathway for pathogens on land to reach the ocean. It can lead to consequences for human and wildlife health, according to a study from the University of California, Davis.

The study, published today in the journal Scientific Reports, is the first to connect microplastics in the ocean with land-based pathogens. It found that microplastics can make it easier for disease-causing pathogens to concentrate in plastic-contaminated areas of the ocean.

The pathogens studied — Toxoplasma gondii, Cryptosporidium (Crypto) and Giardia — can infect both humans and animals. Moreover, the World Health Organization recognizes them as causes of illness. That’s from shellfish consumption and is found throughout the ocean.

“It’s easy for people to dismiss plastic problems as something that doesn’t matter for them, like, ‘I’m not a turtle in the ocean; I won’t choke on this thing,’” said corresponding author Karen Shapiro, an infectious disease expert and associate professor in the UC Davis School of Veterinary Medicine. “But once you start talking about disease and health, there’s more power to implement change. Microplastics can actually move germs around, and these germs end up in our water and our food.”

A human and animal problem

Microplastics are tiny plastic particles smaller than 5 millimeters, no bigger than a grain of rice. They’ve contaminated waters as remote as Antarctica. The study’s findings indicate that, by hitchhiking on microplastics, pathogens can disperse throughout the ocean. Therefore, reaching places a land parasite would normally never be.

T. gondii, a parasite found only in cat feces, has infected many ocean species with the disease toxoplasmosis. UC Davis and its partners have a long history of research connecting the parasite to sea otter deaths. It also kills critically endangered wildlife, including Hector’s dolphins and Hawaiian monk seals. Moreover, in people, toxoplasmosis can cause lifelong illnesses, as well as developmental and reproductive disorders.

Crypto and Giardia cause gastrointestinal disease and can be deadly in young children and people who are immunocompromised.

“This is very much a problem that affects both humans and animals,” said first author Emma Zhang, a fourth-year veterinary student with the UC Davis School of Veterinary Medicine. “It highlights the importance of a One Health approach that requires collaboration across human, wildlife, and environmental disciplines. We all depend on the ocean environment.”

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