Dual parasitic infections deadly to marine mammals
An NIH study finds that seal, sea otter and porpoise deaths are linked to co-infection with two parasites normally found in land animals.
Balintfy: A study of tissue samples from 161 marine mammals that died between 2004 and 2009 in the Pacific Northwest has shown an association between severe illness and co-infection with two kinds of parasites. Dr. Michael Grigg, an investigator at the National Institutes of Health says, what’s surprising is that the two parasites are normally found in land animals.
Grigg: One of them is toxoplasma which is a parasite that's common to cats and the other is sarcocystis which is common to opossums. And we've often heard about these two parasites.
Balintfy: For example, pregnant women are often warned not to change kitty litter because of toxoplasma.
Grigg: And the opossum parasite sarcocystis is one that the horse industry worries about because it can cause equine encephalitis.
Balintfy: Encephalitis is swelling in the brain. But the big question raised by this study:
Grigg: How are these land animal parasites getting into and infecting these marine mammals?
Balintfy: Dr. Grigg theorizes that the parasites are getting into soil; and then, where there’s enough seasonal rainfall, like the Pacific Northwest, they’re getting washed into waterways where they get picked up in live bait fish or shellfish which are in turn eaten by marine mammals.
Grigg: Essentially all marine mammals were showing up. So it wasn't just that these parasites were infecting, say, a harbor porpoise or a harbor seal. It was infecting, we found whales, Dall's porpoises. We had Guadalupe fur seals, California sea lions, on harbor porpoises and harbor seals.
Balintfy: He notes that these parasites are tough, essentially like eggs.
Grigg: And inside these eggs are the infectious forms of the parasite and they're highly stable in the environment. So they can actually persist for up to five years and remain infective. All they need are moist conditions. And you can actually input them into chlorine bleach 100% and it doesn’t kill them.
Balintfy: Meaning there is a risk for human infection as well. But Dr. Grigg says that people can easily avoid the parasites by filtering or boiling untreated water and notes that filtration eliminates them from the water supply. But the study focused on some of the more than 5,000 dead marine mammals reported on the coastal beaches of the Pacific Northwest.
Grigg: What was intriguing was that we found that some of them were infected with sarcocystis and others were infected with toxoplasma. And it wasn’t until we saw the dual infection. So when they're infected with both parasites that we saw disease. These parasites are active in the brain and in the spinal fluids. And in those animals that were dually infected with both parasites, the inflammation and the swelling in the brain, I mean these were the primary reasons for death.
Balintfy: The study results also hint that animals with lowered immunity, such as pregnant or nursing females or very young animals, were more likely to have worse symptoms when co-infected with both parasites. Dr. Grigg stresses the importance of identifying the way that these parasites travel from wild and domestic land animals to marine mammals.
Grigg: So co-infection is clearly bad and therefore how these two parasites are getting into the marine waters is what we have to actually try to stop in order to protect the marine mammals. So maybe it's not a good idea to train your cat to defecate in the toilet or to flush kitty litter down the drain. Those sorts of things could happen. But I think the problem is more not with your kitty cat in the house. It's probably going to be what the wild cats, the bobcats, the mountain lions, cougars, and such. They're the ones that you can't really contain.
Balintfy: Opossums also, which gradually have been expanding their range northward from California and can shed an infectious form of the parasites in their feces. Dr. Grigg suggests vaccination efforts and the importance of having marine marshes to help filter out the parasites before they get to open waterways. For more information on this study and research on these parasites, visit www.niaid.nih.gov. This is Joe Balintfy, National Institutes of Health, Bethesda, Maryland.
About This Audio Report
Reporter: Joe Balintfy
Sound Bite: Dr. Michael Grigg
Topic:parasite, parasitic infection, marine mammal, porpoise, seal, whale, co-infection, Sarcocystis neurona, sarcocystis, Toxoplasma gondii, toxoplasma, cat, wild cats, opossum, encephalitis, brain swelling
Additional Info: Dual parasitic infections deadly to marine mammals