ST. LOUIS—Parasites from cat feces are causing deadly brain damage in California sea otters. A combination of toxic chemicals and herpes virus is killing off California sea lions.

And toxic algae blooms are contributing to record manatee deaths in Florida.

All of these animals live near coastlines, spending a majority of their lives in the same waters people swim and surf in. Their daily cuisines consist of the same foods we serve up in clam shacks and fine seafood restaurants.

The difference between humans and these animals, says NOAA spokesperson Paul Sandifer, is that the animals deal with the ocean conditions, good or bad, full time. People can pick and choose when to go into the water and what to eat.

As a result, marine animals, particularly mammals, play an important role as sentinel species. When one of these species gets sick or dies from something in the water, it is often a warning to humans of disease to come.

"Some of what we throw or flow into the water will return to bite us in the gluteus maximus. You can bet on it," said Sandifer, who organized a panel of marine scientists to present their work here last week at the annual meeting of the American Association for the Advancement of Science.

Red tide

The red tide algae blooms that turn waters off Florida's coast rust-colored are becoming more frequent. Karenia brevis algae, responsible for red tide, produce toxins called brevetoxins, which can kill fish, sea turtles, birds, and marine mammals such as manatees.

The toxins seem to be sending more people to emergency rooms, too, said Gregory Bossart of the Harbor Branch Oceanographic Institution.

In 2005, 151 manatees died from exposure to brevetoxin. Post-mortem examinations revealed that the stuff was affecting their lungs.

"The animals are actually hemorrhaging into their lungs," Bossart said. "They're dying of acute toxic shock."

Airborne brevetoxins, Bossart said, can affect human respiratory systems the same way as a bad cold. A five-year study revealed that emergency room admissions for respiratory illness, including pneumonia and asthma attacks, increase by 54 percent during red tide blooms.

"While the toxin may not kill you, it will make you sick and immuno-suppressed. It may make you susceptible to other infections," Bossart said. "What's disturbing is that humans appear to respond to prolonged brevetoxin exposure in a way similar to manatees that die from it."

Bossart recently published evidence that algae blooms may be of danger to humans and marine animals even after they disappear.

Brevetoxins collect in filter-feeding shellfish. Within hours of ingesting shellfish with high levels of the toxin, humans can experience temporary neurotoxic shellfish poisoning (NSP). Symptoms of NSP include nausea and diarrhea, dizziness, muscle aches, and tingling and numbness in the tongue, lips, throat, and extremities.

Currently, scientists only monitor shellfish during a bloom. But Bossart discovered that the concentration of brevetoxins in the water and in sea grass continued to increase months after blooms faded.

"After the bloom, the toxins persist in some of the same food items that we eat," Bossart told LiveScience.

Deadly cat poop

A deadly parasite that's the third most common cause of death due to food-borne disease in the U.S. is also killing California sea otters at a rapid rate.

Toxoplasma gondii, which causes the disease toxoplasmosis in humans, has been found in 52 percent of dead otters and 37 percent of the living.

The parasites are tiny, mysterious, and tough, said Pat Conrad of the University of California at Davis. They can invade an organism and stay dormant for years. When the opportunity presents itself, they will emerge from their dormant form and attack the animal's brain.

In otters, the parasite causes tremors, incoordination, and seizures. It is the primary cause of death in some coastal otter populations.

"Some rescued otters need to be hand fed squid, their tremors are so bad," Conrad said.

Thanks, Kitty

But, Toxoplasma gondii can only reproduce in cats, which shed the parasites in their feces. Although cats will only shed new parasites once in a lifetime, millions come out at once.

This happens on land and in kitty litter boxes, though, so how are coastal otter populations becoming infected?

Conrad says the major culprit is freshwater runoff, which washes feces from backyards, streets, and illegally dumped kitty litter into streams, rivers, and ultimately the ocean. Indeed, Conrad's studies have indicated that infection risk potential for otters living near freshwater runoff increases three times. For the otters of Morro Bay, the risk is more than nine times increased.

Cat owners should try to keep their kitties indoors and to properly dispose of kitty litter at a landfill to reduce the risk of spreading parasites, Conrad said. She also notes that eco-friendly, flushable kitty litter may contribute to the problem since sewage treatment systems do not effectively eliminate the parasite from wastewater.

Scientists estimate that up to 25 percent of the U.S. population may be infected with this same parasite, but people rarely show symptoms. If they do, it might just appear as a flu-like illness.

Pregnant women infected with the parasite can pass it on to their developing babies, increasing the chance of an abortion or miscarriage. If a baby survives, it could have severe brain damage that may or may not be evident at birth.

Of the infected otters, 72 percent harbor a parasite strain not seen often in humans. Otters cannot pass the parasite to humans, but because of their chronic exposure, they act as an early warning for people.

Sea lion cancer

For California sea lions, a combination of persistent organic pollutants (POPs) and herpes virus similar to the one that infects humans has led to an increase in cancer.

Over the past 15 years, 17 percent of dead and stranded sea lions have been diagnosed with urogenital cancer, striking females in the cervix and males in the penis and prostate.

The cancer spreads to other organ systems in sea lions the same as in humans. Eventually it erodes the spinal cord, paralyzing them and causing them to wash up on the shore or strand in the open water, said Frances Gulland of the Marine Mammal Center.

Many adult sea lions also have the herpes virus—up to 43 percent of males and 23 percent of females. The higher rate for males is because it is a sexually transmitted disease, Gulland said, and males have more sexual partners.

But, since some herpes-infected animals are without cancer, Gulland suspects that POPs, which can cause cancer on their own, are teaming up with the virus to increase cancer rates.

While POPs are in the water, sea lions are exposed to them mainly through the food they eat, in which the toxic chemicals accumulate.

"These are top level predators," Gulland said. "Like us, they eat anchovies, squid, salmon, and mussels—they are sentinels for human health because they share our ecosystems and prey. We may see impacts in sea lions before people—they could be an early warning."