Caused by a common parasite that infects many animals, toxoplasmosis is a serious concern for the health of threatened species like the southern sea otter and the endangered Hawaiian monk seal.
September 6, 2017
When a southern sea otter was spotted rubbing his belly on a northern California beach rather than frolicking amongst the kelp, The Marine Mammal Center’s trained responders knew the animal was in distress. The otter, later identified as an adult male, was admitted to the Center’s hospital on the evening of July 3. Center volunteers aptly named him Yankee Doodle in honor of the Fourth of July holiday.
Yankee Doodle was placed in one of the Center’s newly retrofitted otter pens, separated by a pen of sea lions from our other sea otter patient, Otto, to prevent the territorial adult male otters from fighting. During an initial admit exam, Yankee Doodle exhibited signs of neurological disease in addition to being lethargic, underweight and malnourished for his age. The veterinary team ordered an MRI and some additional tests, and started Yankee Doodle on a rich diet of restaurant-quality shrimp, clam, squid and mussels.
Like Otto, Yankee Doodle's MRI showed signs that he was suffering from domoic acid poisoning after eating shellfish contaminated with a toxin produced by harmful algal blooms. But his bloodwork indicated that he was also battling another potentially lethal condition: toxoplasmosis.
Caused by a common parasitic protozoan called Toxoplasma gondii, toxoplasmosis can cause fatal brain infections in sea otters and other animals. While the parasite can infect most birds and mammals, it can only reproduce in cats. Both domestic and wild cats, such as bobcats and cougars, shed the parasite’s oocysts, or egg-like structures, in their droppings.
How does a parasite infect a sea otter?
These robust oocysts are able to survive for months in extreme environmental conditions. Once they reach the ocean, the oocysts can be inadvertently consumed by marine animals. For example, sticky substances secreted by seaweed may allow the oocysts to adhere to kelp, which is eaten by turban snails. Sea otters preying upon the infected turban snails may then become infected too.
Toxoplasma oocysts can also remain suspended in the water column, slowly making their way to the seafloor as marine snow. The oocysts have been shown to accumulate over time in the tissue of filter feeders like clams, mussels and scallops, which are all primary prey items for sea otters. The oocysts may also be ingested by otters during their frequent grooming sessions to keep their thick fur in good condition.
A variety of parasite infections are common in wild populations, and we often see heavy parasite loads in our patients at the Center. But toxoplasmosis is especially concerning because it is a significant cause of death in southern sea otters, which is already a threatened population.
Endangering another population
In 2004, less than 10 years after researchers began documenting the impacts of toxoplasmosis on the sea otter population in California, the first fatal infection was observed in Hawaiian monk seals, an endangered species.
Since then, researchers have confirmed a total of eight monk seal deaths due to toxoplasmosis, though that’s a minimum number because some monk seals die undetected. For a population of just 1,300 animals, this is a major threat to the species’ survival.
In monk seals, toxoplasmosis can cause fatal damage to multiple organs, including the heart, liver and brain. Although some seals survive the infection, they can suffer from compromised immune systems or brain damage that limits their ability to handle other environmental stressors.
Like sea otters, monk seals may be exposed to the Toxoplasma oocysts directly in the water or by eating other animals that have ingested them. Although it’s possible the parasite has always existed in the marine environment, most scientists think it’s directly due to oocysts dropped by cats reaching the ocean.
© NOAA permit #16632
A parasite’s path from land to sea
Toxoplasma oocysts are hardy enough to survive sewage treatment processes, so it’s possible that dirty kitty litter flushed down the toilet could carry the parasite out to sea. However, there is little evidence that animals living near sewage outflows are disproportionately affected by the parasite.
Instead, researchers have found that otters living near the mouths of rivers and streams are three times more likely to be exposed to Toxoplasma, which suggests that storm water runoff from areas frequented by cats may be a larger part of the problem. Runoff increases with the built environment as concrete and other impervious surfaces prevent rainwater from draining naturally.
The destruction of natural wetlands also reduces their important filtering capacity, which could prevent Toxoplasma and other fecal pathogens from reaching rivers, streams and the ocean.
Because both sea otters and Hawaiian monk seals spend much of their time in coastal and nearshore environments, they are clearly heavily impacted by human activity in these areas. But even areas far inland can have an impact on these threatened species as runoff enters the watershed and travels downstream to their ocean home.
How you can help
As a cat owner, there are several things you can do to help alleviate the problem. If you keep your cat indoors, be sure to dispose of the cat litter in the trash instead of flushing it down the toilet. If you allow your cat outdoors, maintain a litterbox outside as well and dispose of any waste in the trash. By spaying or neutering your outdoor cat, you can also help reduce the number of cats spreading Toxoplasma in the wild.
But this problem isn’t just about cats. It’s also important to support conservation and reconstruction of wetlands and other natural areas near the ocean. And don’t forget your own backyard: when landscaping, consider natural landscaping features such as native grasses and a rain garden to absorb runoff and filter out contaminants.
Sea otters as sentinels of ocean health
Making changes like these to help reduce the spread of Toxoplasma benefits more than just sea otters and Hawaiian monk seals—it can help keep humans safe as well. Although most people exposed to the Toxoplasma parasite through contact with cat waste or contaminated food or water don’t experience noticeable symptoms, those with compromised immune systems, including infants, can develop serious complications.
Toxoplasmosis is just one of many diseases we see in our marine mammal patients that have human health implications. That’s why our work at the Center goes beyond our rescue efforts to focus on scientific research and education as well.
As the world’s largest marine mammal hospital, we’re able to take what we learn from the hundreds of animals we rescue each year to help us all better understand the health of the ocean environment we both share.
Luckily for our sea otter patient Yankee Doodle, he was rescued in time to receive life-saving treatment for both of his neurological conditions. Like Otto, he received fluids to help flush his system of any remaining domoic acid. And to treat his toxoplasmosis, our veterinarians gave him an antibiotic that is known to be effective against Toxoplasma.
Over the last two months, Yankee Doodle’s health and appetite have improved, and he is steadily regaining the weight he lost while he was ill. The Center’s veterinary team is also closely monitoring his behavior to ensure he is not suffering from any permanent brain damage.
Once Yankee Doodle is deemed ready for release, we will monitor his progress in the wild to ensure his continued health and better understand the potential long-term impacts of toxoplasmosis on the sea otter population.
You Can Make a Difference
Because of the special diets and environments needed to rehabilitate sea otters and Hawaiian monk seals, you can understand why their care requires significant financial support from caring people like you. Passionate about threatened and endangered species? You can make this life-saving work possible through your support of The Marine Mammal Center today.
Toxoplasmosis Research at The Marine Mammal Center
Over the last two decades, our veterinarians and scientists have contributed to a number of scientific papers on Toxoplasma, some of which can be viewed here:
Carlson-Bremer, D., Colegrove, K.M., Gulland, F.M.D., Conrad, P.A., Mazet, J.A.K., Johnson, C.K. 2015. Epidemiology and pathology of Toxoplasma gondii in free-ranging California sea lions (Zalophus californianus). Journal of Wildlife Disease 51(2).
Conrad, P.A., Miller, M.A., Kreuder, C., James, E.R., Mazet, J., Dabritz, H., Jessup, D.A., Gulland, F., and Griggs, M.E. 2005. Transmission of Toxoplasma: clues from a study of sea otters as sentinels of Toxoplasma gondii flow into the marine environment. International Journal for Parasitology 35: 1155-1168
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