A disease spread by cat feces killed three female Hawaiian monk seals on Oahu in May, the National Oceanic and Atmospheric Administration announced Monday.

The NOAA Fisheries Pacific Island Regional Office said an adult female identified as RK60 was found dead May 15 after being spotted in Kaneohe Bay. A dead pup was found the next day in Laie, and an adult female identified as RT10 was found the day after, on May 17.

All three died of organ failure related to toxoplasmosis, a parasitic disease spread by infected cat feces, said Angela Amlin, Hawaiian monk seal recovery coordinator at NOAA. There have been 11 reported monk seal deaths in the state due to toxoplasmosis, two in 2015. Eight of the deaths were of female monk seals.

“We’ve had a very wet year, and we don’t know what that means for the monk seal population,” said Amlin. “But we do know that … rains can flush fecal matter from the top of the mountains all the way down.”

Amlin warned that the disease is “disproportionately affecting females” and is a cause for concern in terms of reproduction potential. “Whatever pups those females would have given birth to … we’ll now never see those pups,” she said.

With a population of 1,400, the Hawaiian monk seal is one of the most endangered marine mammals in the world, according to data from NOAA.

Toxoplasmosis also is responsible for the death of two spinner dolphins in recent years, and also can infect the nene goose and alala, the Hawaiian crow, said Amlin.

Though more research is needed to determine why female monk seals are particularly vulnerable, Michelle Barbieri, a wildlife veterinary medical officer at NOAA Fisheries’ Science Center, said pregnant seals may not be able to effectively fight off infections, and pups can be exposed to the disease in utero.

Barbieri said toxoplasmosis is “of greatest concern,” as it is the leading disease- related cause of mortality for Hawaiian monk seals.

Monk seals are vaccinated for diseases, but there is no vaccine for toxoplasmosis, said Barbieri.

“Cats are the only known reproductive host of the toxoplasmosis parasite,” wrote the state Department of Land and Natural Resources and Department of Health in a news release. “It reproduces in the feline digestive system. A single cat can excrete 145 billion eggs per year in its feces. Once released into the environment, these eggs can infect other animals, including humans, both on land and in the ocean. Toxoplasmosis parasites create cysts in muscle and organ tissues and can cause inflammation of the heart, liver, and brain.”

Amlin said interrupting the parasite’s life cycle by that removing cats from the landscape is crucial. Keeping cats indoors and feeding them supplements, as well as not feeding the feral cat population are effective methods. Spaying and neutering cats do not prevent toxoplasmosis.

“Feeding cats at state parks, boat harbors and other coastal areas increases the risk of transmission because the cysts don’t need to travel very far to get into the ocean,” said DLNR Chairwoman Suzanne Case. “Frankly, feeding cats anywhere where their feces can ultimately wash into the ocean is a problem.”