Death of spinner dolphin from parasite found in cats spurs concern

Death of spinner dolphin from parasite found in cats spurs concern
(Image: Art Tarsa)
(Image: Art Tarsa)

HONOLULU (HawaiiNewsNow) - The disease primarily spread by cat feces that's threatening Hawaiian monk seal populations killed a spinner dolphin in Hawaii last year, scientists have now concluded.

It's the first documented case of toxoplasmosis killing a spinner dolphin since 1990, though scientists say more study is needed to determine whether a greater threat exists to the animals.

The adult male spinner dolphin that died was found in shallow waters off Hawaii Island, and initial indications were that it had a serious infection.

Subsequent lab tests, which were completed recently, determined that the dolphin died from Toxoplasmosa gondii, a parasite commonly associated with cats. The parasite enters the oceans via cat feces, which gets caught up in polluted runoff.

Kristi West, associate professor of biology at Hawaii Pacific University and director of the state's marine stranding program, said the case is a serious wake-up call for Hawaii conservationists.

"It's really concerning for us," she said. "Is this a population threat to spinner dolphins like it is for Hawaiian monk seals?"

The conclusion has prompted West to launch a new examination of previous necropsy samples in her lab, dating back to 1997. West and her team are responsible for determining the cause of death for all whales and dolphins that die in Hawaii waters.

She said her lab will conduct a retrospective analysis of samples from 22 dead spinner dolphins that were never tested for toxoplasmosis.

Toxoplasmosis has already been identified as a significant threat to Hawaiian monk seals, which congregate on shore and in near-shore waters. Spinner dolphins are near-shore animals, West said.

Late last year, a monk seal that died near the Ala Wai Boat Harbor tested positive for Toxoplasmosa gondii. The death brought to eight the number of monk seals in the main Hawaiian islands known to have died from toxoplasmosis

The parasite lives in the muscle tissue of host animals (rodents and small birds). When cats eat those small animals, the parasite reproduces in their digestive tracts and is released into the environment through their feces.

Toxoplasmosa gondii is common in both feral and household cats in Hawaii, and cats are the only known animal in which Toxoplasmosa gondii eggs are reproduced, which is why scientists have called on the state to control the feral cat population in order to reduce the risk of the parasite spreading.

"The vector is really cat feces that get into the watershed, and it's very persistent," West said.

Infected cats oftentimes don't show any effects from the parasite. In monk seals, dolphins and other marine animals, the parasite infects tissue, causing or contributing to death.

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