8: Watch wildlife health

Within an ecosystem, wild animals and humans share many diseases and are susceptible to many of the same toxins. Studying diseases and contaminants in wildlife help us to better protect them and help prevent disease in people.

Diseases and contaminants that impact wildlife, like this Steller sea lion, also can impact humans. Monitoring wildlife health shows us where a stressed ecosystem contributes to increased disease in people and wildlife. Photo: A. Traxler

Disease in marine wildlife can serve as a sentinel for human health. Animals, particularly wildlife, are thought to be the source of over 70% of all emerging infections. A burgeoning human population, increased travel opportunities, booming commerce, frequent animal relocations, and expanding aquaculture increase human exposure to zoonotic diseases from marine wildlife.

Blooms of the phytoplankton Pseudo-nitzschia have caused closures of recreational, commercial, and tribal subsistence shellfish harvest in the Salish Sea.  These organisms produce domoic acid, a biotoxin known to cause seizures and death in marine mammals and amnesic shellfish disease in humans. Marine mammals are exposed by eating fish that have consumed domoic acid. Exposed animals often will strand on beaches and can serve as an early warning indicator for potential exposure of humans through shellfish consumption, thereby allowing managers to close shellfish harvesting areas to protect human health.

Discovering that the feline parasite Toxoplasma gondii infected marine wildlife alerted people to the fact that raw shellfish consumption also could be a route of exposure for humans. If a pregnant woman becomes infected with this parasite the parasite can infect the fetus, leading to mental retardation, seizures, blindness and death in children. Interestingly, this cat parasite has been discovered to infect marine wildlife such as sea otters, marine-foraging river otters and harbor seals. It is believed that marine wildlife are exposed to T. gondii when cats shed the infective stage (oocyst) in feces, which is then transported by freshwater run-off into the marine ecosystem. Increased numbers of domestic and feral cats and their associated feces as well as modifications in freshwater run-off have probably increased marine mammal exposure to this parasite. Because shellfish can concentrate the infective T. gondii oocysts, humans, like marine mammals, also are at risk for exposure by eating uncooked shellfish.

Human, wildlife and ecosystem health are intimately connected. Understanding and monitoring diseases in both groups will help to identify where and when a stressed ecosystem is contributing to increased disease in people and wildlife and how the ecosystem can be redesigned. In the Salish Sea region high-quality public health programs exist but efforts to monitor and understand marine wildlife health in both countries are limited and not well linked to human health networks.