The Shark Immune System | When Sharks Attack

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NARRATOR: As experts begin to search for other explanations, they turn their attention to a series of disturbing discoveries that occurred in the months following the June 2012 attacks. We had some dolphins that washed up already dead. We weren't really sure what it was, but we did hear from other states that they were having the same issue.

NARRATOR: In fact, it turns out that over the course of 2013, a total of 48 dolphins are found dead on South Carolina beaches. Researchers concluded the dolphins were inflicted with the morbillivirus. This deadly disease suppresses the dolphin's immune system and causes inflammation of the brain. The result is a bizarre shift in behavior. Infected dolphins have been witnessed swimming in strange patterns, almost like they are drunk.

And additional research has shown that brain inflammation in zebrafish caused them to become more agitated. So in 2012, could the sharks of Myrtle Beach have been inflicted with a disease that changed their behavior, making them more likely to bite swimmers? According to Dr. Dan Huber, it comes down to a shark's immune system.

DAN HUBER: For animals, the skin is the first line of defense against any type of an infection. So the skin is part of the immune system, essentially. Looking at a section of shark skin which shows what are called dermal denticles, which are basically little teeth that make up the scales of a shark.

NARRATOR: The denticles perform a unique function in the shark's immune system.

DAN HUBER: Dermal denticles creates a very uneven shape that bacteria have a hard time adhering to. Because the bacteria can't adhere to it, they can't form colonies. And this is something that helps sharks to resist bacterial infections.

NARRATOR: And there's also another organ that helps protect sharks from disease-- their liver. The liver produces a chemical compound called squalamine. The squalamine is dispersed inside the shark's cells. If a virus invades the cells, the squalamine prevents it from multiplying so the virus doesn't spread. And the shark doesn't get sick. Scientists are even testing squalamine to fight cancer in humans.

This remarkable immune system means that sharks might be one of the most disease-resistant creatures on Earth. Any suggestion that the sharks could have become ill due to a virus or a bacterial infection isn't very likely because sharks have very strong immune systems.