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[music playing]
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NARRATOR: As experts begin to search for other explanations,
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they turn their attention to a series
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of disturbing discoveries that occurred
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in the months following the June 2012 attacks.
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We had some dolphins that washed up already dead.
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We weren't really sure what it was,
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but we did hear from other states
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that they were having the same issue.
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NARRATOR: In fact, it turns out that over the course of 2013,
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a total of 48 dolphins are found dead on South Carolina beaches.
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Researchers concluded the dolphins were inflicted
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with the morbillivirus.
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This deadly disease suppresses the dolphin's immune system
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and causes inflammation of the brain.
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The result is a bizarre shift in behavior.
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Infected dolphins have been witnessed
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swimming in strange patterns, almost like they are drunk.
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And additional research has shown
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that brain inflammation in zebrafish
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caused them to become more agitated.
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So in 2012, could the sharks of Myrtle Beach
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have been inflicted with a disease that
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changed their behavior, making them
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more likely to bite swimmers?
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According to Dr. Dan Huber, it comes down
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to a shark's immune system.
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DAN HUBER: For animals, the skin is
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the first line of defense against any type
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of an infection.
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So the skin is part of the immune system, essentially.
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Looking at a section of shark skin which shows what
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are called dermal denticles, which
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are basically little teeth that make up the scales of a shark.
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NARRATOR: The denticles perform a unique function
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in the shark's immune system.
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DAN HUBER: Dermal denticles creates
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a very uneven shape that bacteria
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have a hard time adhering to.
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Because the bacteria can't adhere to it,
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they can't form colonies.
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And this is something that helps sharks
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to resist bacterial infections.
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NARRATOR: And there's also another organ that helps
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protect sharks from disease--
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their liver.
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The liver produces a chemical compound called squalamine.
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The squalamine is dispersed inside the shark's cells.
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If a virus invades the cells, the squalamine
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prevents it from multiplying so the virus doesn't spread.
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And the shark doesn't get sick.
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Scientists are even testing squalamine to fight cancer
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in humans.
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This remarkable immune system means
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that sharks might be one of the most
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disease-resistant creatures on Earth.
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Any suggestion that the sharks could have become ill due
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to a virus or a bacterial infection
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isn't very likely because sharks have
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very strong immune systems.
