The Inter-Research Science Publisher published findings this week on two stranded spinner dolphins in Hawaii that died from toxoplasmosis, an infection caused by a parasite, according to Kristi West, the Health and Stranding Lab director at the University of Hawaii Manoa who contributed to the research.

West and her colleagues closely studied 51 whales and dolphins across 18 different species that were all stranded. The two spinner dolphins found in Hawaii were the only ones that tested positive for toxoplasmosis. Though West said it should be noted that there were only one to three individuals of each species, and results would likely differ with a larger sample size.

spinner dolphin death from toxoplasmosis
This spinner dolphin was found on the Big Island in 2015. Researchers later determined it died from toxoplasmosis. Courtesy: Hawaii News Now

The first report of a spinner dolphin that died from toxoplasmosis was in 1990, found on the North Shore of Oahu in Haleiwa, which scientists thought was a rare occurrence, according to West. The next was found beached on the Big Island in 2015, which West said spurred the research in their paper. The most recent dolphin that died from the parasite was found floating near the shores of Waianae, on the west coast of Oahu in 2019.

While a lot of birds and mammals, such as cats, monk seals, pigs and rodents can get infected, the parasite only reproduces in the digestive system of a cat, West said. To date, the parasitic disease has been the primary cause of death for at least 14 critically endangered Hawaiian monk seals.

The parasite’s eggs are shed in cat feces which is why, as a precaution, people who are immunosuppressed or pregnant are often advised to refrain from changing litter boxes. If the parasite is accidentally ingested, it can cause severe lung or brain disease, and consequences for the fetus are severe, West said.

Studies in California have shown that marine invertebrates, such as crabs and clams, have accumulated a part of the parasite after rain and runoff, and sea otters that ingested the infected marine invertebrates later developed the disease, according to a UH press release.

West said it’s also likely that marine invertebrates and fish that harbor the parasite are swept downstream from watersheds, leading to the infection of nearshore spinner dolphins.

RN36, commonly known as Uilani, rests on the shoreline. The endangered Hawaiian monk seal died of toxoplasmosis in 2015. Courtesy: NOAA Fisheries

Generally, many people can test positive for toxoplasmosis and won’t have any symptoms, and it won’t cause any damage.

“But with dolphins, we learned that if they’re infected with toxoplasmosis — they die,” West said. “Every single organ system had incredible inflammation and dysfunction … it’s a little bit of all or nothing.”

Since the UH Health and Stranding Lab only recovers and examines about 5% of the spinner dolphins that die in Hawaiian waters, it’s possible that at least 60 spinner dolphins may have died of toxoplasmosis, according to the research.

The public can help reduce the spread of toxoplasmosis through responsible cat ownership by spaying or neutering cats, keeping cats indoors and reporting any illegal dumping of cats or kittens outdoors into feral colonies, according to a UH press release.

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