Researchers at the University of Hawaii at Manoa’s Health and Stranding lab have determined that two spinner dolphins that were stranded in separate incidents died from toxoplasmosis.

Toxoplasma gondii, the parasite that causes toxoplasmosis, is present in invasive species such as pigs, mongoose, chickens and cats.

One of the dolphins was stranded on Hawaii Island in 2015; the other was stranded on Oahu in 2019.

The researchers screened archived tissues from past dolphin and whale strandings and did not find the parasite present in any the marine animals except those that died from it. According to the team, this demonstrates that if a spinner dolphin has a severe toxoplasmosis infection, it will die.

“We suspect that many more spinner dolphins may succumb to toxoplasmosis and die than the animals that are recovered dead and examined for cause of death,” said Kristi West, associate researcher at UH Manoa’s Hawaii Institute of Marine Biology and director of the UH Health and Stranding Lab. “A better understanding of toxoplasmosis infections and infectious cycles is important to developing effective conservation strategies for protected and endangered Hawaiian wildlife.”

The team’s findings were published in the journal Diseases of Aquatic Organisms.

Toxoplasma gondii reproduces in the digestive systems of cats, which shed the eggs, called oocytes, in their feces. The oocytes can remain viable for up to two years and can infect monk seals, dolphins and whales when washed out to sea.

The strain of toxoplasmosis found in both dolphins is the same one identified in feral pigs on Oahu in 2020.

There are three documented cases of dolphins dying of toxoplasmosis in Hawaiian waters since 1990, but the researchers believe the actual figure is at least 60.