Pollution and contamination in the oceans off the coast of the United Sates may be having severe effects on the health of dolphins. A new study, published in PLOS ONE, has found that the immune systems of wild dolphins are dangerously compromised when compared to dolphins in captivity.
“The immune system is incredibly complex and so very important for health. Microbes are part of the natural world and help to develop the immune system,” explained Dr Gregory Bossart, who co-authored the paper. “The key to a healthy immune system is a balance between being able to recognize harmful organisms and overstimulation, and this study demonstrates the importance of the environment in these responses.”
Obviously, dolphins living in the wild will have more active immune systems than their captive counterparts, simply because they are encountering more pathogens as they go about their daily lives. But the researchers found that the wild dolphins’ immune systems were being overly stimulated, which has a knock-on effect on how they deal with other infections.
After studying the populations of dolphins living in the Indian River Lagoon and Charleston over the last 14 years, the scientists got some startling results. The levels of contamination from anthropogenic pollution is alarmingly high, with those in the Indian River Lagoon having particularly worrying levels of mercury in their systems. This is thought to be due to it building up through the ecosystem, in what is known as bioaccumulation.
It had previously been found that the wild dolphins were subject to cutaneous fungal infections, and the researchers suggest that this could be related to how their immune system is being suppressed as a result of the high pollution levels. They also note that the cetaceans are subject to other new emerging viruses and infectious agents.
“Importantly, the chronic immune system activation as found in the wild dolphins of this study could lead to eventual immunologic dysregulation and the inability to eliminate chronic inflammation,” said Dr Bossart.
The researchers suggest that their findings in the dolphins may have profound impacts on the people living in the same regions. If the dolphins, for example, have high levels of mercury in their bodies due to bioaccumulation from eating contaminated fish, then people who are also eating large quantities of locally caught fish may also be at risk.
The immune-compromised dolphins may also be a threat to human health by increasing the chance that they will spread viruses and diseases to people. Known as a zoonotic disease, the spread of infection from animals to humans is actually quite a common occurrence around the world, but the worry is that the situation with the dolphins is simply increasing the stakes.