LIHUE — Monk seal monitors are keeping a sharp eye on The Garden Island’s Hawaiian monk seal population after scientists confirmed toxoplasmosis as the cause of death for three Oahu seals in early May.
That’s according to veterinarians from the National Oceanic and Atmospheric Administration who investigated the three deaths.
“Toxoplasmosis is tough to diagnose because most times you can’t tell anything is wrong with the seal,” said Angela Amlin, Hawaiian monk seal recovery coordinator for NOAA.
She continued: “We’re keeping an eye out for logging, which is when they’re kind of floating lethargically and it’s also part of the reason we ask the public to call in sightings. You never know.”
In Hawaii, the National Oceanographic and Atmospheric Administration has recorded at least 11 Hawaiian monk seal deaths that are attributable to toxoplasmosis infection since the first confirmed deaths in 2001.
Three of those were on Kauai — one in 2004, one in 2006 and one in 2010.
“Interestingly, those were the only males that have been impacted,” Amlin said. “Otherwise, it’s been disproportionately impacting females which is not great. That has a bigger impact on the population.”
Seals are most likely getting it from their prey or from direct exposure to the parasite in their ocean environment and monk seal monitors have notched up their toxoplasmosis testing on seals over the past few years.
Cats are the culprit for spreading the disease, according to Hawaii’s Department of Land and Natural Resources, as the toxoplasmosis parasite requires the feline digestive system to reproduce and complete its lifecycle.
A single cat can excrete 145 billion eggs per year in its feces, according to DLNR.
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.
“In addition to impacting marine mammals and wildlife, toxoplasmosis is a risk to humans. It is known to cause serious problems for pregnant women and their unborn children,” said Health Director Bruce Anderson.
He continued: “During pregnancy, infection by the toxoplasmosis parasite can damage the unborn child, causing miscarriages, stillbirth, or substantial birth defects including enlargement or smallness of the head.”
Healthy individuals usually experience benign symptoms if they get a toxoplasmosis infection with a few people experiencing flu-like symptoms. Most probably don’t know they’ve been infected, according to the state Department of Health.
“The only thing certain about toxoplasmosis is that there are far more cases in humans and more deaths in seals, dolphins, native birds and other animals today than are recognized and reported,” said Anderson. “Since cats are the only animal that transmit the disease, it only makes sense that reducing the number of feral cats will reduce the risk of infection and serious illness or death.”
Basil Scott of the Kauai Community Cat Project said his and other organizations like KCCP are taking effective action to prevent issues caused by cats through capture and sterilization.
“In addition, our approach directly combats toxoplasmosis by ensuring that prevalence is dramatically reduced for cats that do live outside,” he wrote. “Scientific studies conducted in California has validated our approach by showing a reduction of 80 percent in the prevalence of toxoplasmosis in homeless cats.”
Based on National Institutes of Health data, the prevalence of exposure to toxoplasmosis in humans is declining significantly, Scott said. Prevalence means an exposure to the parasite, not sickness, he added.
In 1990, the age-adjusted prevalence was 14.9 percent. In 2014, it was under 6 percent. Data from intermediate years shows that this decline has been continuous and that it continues today, he said.
“It is very unfortunate that seals die from this disease, but fortunately, NOAA data, both seal necropsy data and seal health screen data, show that the prevalence in seals is very low. However, it is a risk that seals in the Main Hawaiian Islands face,” Scott wrote. “Given this, DLNR should support programs like ours which are shown by Kauai data and scientific studies to most effectively reduce the risk.”
Trap-neuter-release programs, Mobile Animal Sterilization Clinics and other methods are currently being employed throughout the islands to control the feral cat populations.
In addition to population reduction, DLNR suggests not feeding cats near sources of water or the ocean because it increases the risk of transmission. But, officials say it might not matter where the cats are congregating because watersheds push runoff to the ocean anyway.
“The cysts can live for months in soil and can wash into streams and runoff and be carried into the ocean from almost anywhere. 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 chair Suzanne Case. “Frankly, feeding cats anywhere where their feces can ultimately wash into the ocean is a problem.”
Spinner dolphins are the only other marine species that have been documented as dying from toxoplasmosis in Hawaii, according to DLNR. Toxoplasmosis can also infect Hawaii’s native birds, including the nene and the newly released Hawaiian crow, the Alala.