California Coast & Ocean

Some 18 years ago, I went to visit an old friend who was several months pregnant. She was giving me a tour of her new house, and when we arrived on the screened-in back porch she made a curious request: "Would you mind very much cleaning the cat's litter box for me?" I surely gave her a look, and she explained: "My doctor told me under no circumstances was I to clean it out myself because of a disease that can spread to human embryos. So I'm relying on family and friends to do the job."

The disease is called toxoplasmosis, and it is a parasitic infection that may be found in more than 60 million Americans--one-fifth of the population. How do we get it? Typically by eating undercooked, infected meat of animals that serve as an intermediate host (pigs, sheep, and rabbits are a few of them), or by contact with cat feces. For the protozoa Toxoplasma gondii, cats are the definitive host--the only organism in which the parasite reproduces. If a cat eats a rodent that has been infected with T. gondii, the little parasite can celebrate, because it is home at last, able to do what it was meant to do and complete its life cycle. Eventually its eggs (called oocysts) are shed all at once and by the tens of millions, in cat feces.

Most humans never know they have the disease. Healthy people tend to be asymptomatic, although some may develop flu-like symptoms that quickly vanish. Those at risk for the more serious consequences of toxoplasmosis are babies in utero and people with compromised immune systems. When passed on congenitally, toxoplasmosis may result in blindness and mental retardation; in immunosuppressed victims, it can cause encephalitis and, ultimately, coma and death.

Recently, I reencountered toxoplasmosis--not in humans, but in sea otters (Enhydra lutris). While most infected humans go through life blithely unaware of their predicament, sea otters are not necessarily so fortunate. In a study of freshly dead beach-cast sea otters collected from 1998 to 2001, toxoplasmosis was the primary cause of death in 17 percent of cases. In addition, researchers found that brain inflammation resulting from the infection led to a 3.7 times greater risk of death due to shark attack or boat strike.

But how can this be? Sea otters don't eat mutton or pork, or even rodents, and they aren't exposed to cat feces. Or are they?

It turns out they are. Or at least, to the microscopic T. gondii oocysts that are carried in the feces. The likely mode of transmission is freshwater runoff--not just along the California coast, but inland as well. Anywhere rain falls and washes into rivers that in turn flow into central California coastal waters, cats--domestic, feral, and wild (bobcats, mountain lions)--defecating outdoors contribute to serious disease in otters. Even indoor cats that use litter boxes are culprits, if their owners buy flushable litter for ease of use and send the feces into the sewers. Studies have found that urban centers along the coast, and points of heavy freshwater outflow such as the Salinas River, correlate strongly with high rates of infection in otters.

Scientists began to document toxoplasmosis as a killer of sea otters in 1998. The evidence they presented was so convincing that in September 2006, the California Legislature passed, and Governor Arnold Schwarzenegger signed, Assembly Bill 2485 in an effort to mitigate the problem. A major component of the bill, which took effect in January, calls for labels on cat litter packaging advising consumers that "encouraging your cat to use an indoor litter box, or properly disposing of outdoor cat feces, is beneficial to overall water quality."

Unsettling Trends
Unfortunately, toxoplasmosis is only one hazard that sea otters face. Other protozoal parasites, tiny worms, fungi, persistent organic pollutants (POPs), pesticides, fishing pots, boats, and even marine algae also play deadly roles. Currently, deaths are outpacing births among southern sea otters, and researchers are trying to understand why.

Their answers may determine whether we will be able to continue enjoying the presence of this lovable icon of the California coast.

As recently as the mid-17th century, an estimated 16,000 sea otters foraged and raised their young along the California coast. Hunting diminished their numbers so thoroughly that by the turn of the 20th century most experts believed the southern sea otter had been wiped out. But then, in the 1930s, a small colony of 50 or so individuals was discovered off Big Sur. In 1983, when the U.S. Geological Survey (USGS) began annual censuses, sea otters had expanded both their range and their number--to 1,277--with slow increases continuing into the early 1990s. Then growth slowed, and in some years counts showed a decline in number. Although the 2004 census recorded a population high of 2,825, by 2006 only 2,692 animals were counted. As Jim Curland of Defenders of Wildlife put it, "The population has flat-lined." The 2007 census will be pivotal: if numbers are down yet again, we'll be looking at a trend of shrinking population.