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A Mysterious Zombie Parasite Is Killing Off Sharks

Meet Miamiensis avidus, the brain-eating zombie parasite killing thousands of sharks in San Francisco Bay.


Over the past few months, thousands of sharks have died in the San Francisco Bay, and scientists were stumped. A new investigation by NBC Bay Area found that as many as 2,000 leopard sharks, 500 bat rays, hundreds of striped bass and halibut, and 50 smooth-hound sharks have died in the first half of 2017.

Leading the charge is a scientist named Dr. Mark Okihiro, who researches the species of the San Francisco Bay with the California Department of Fish and Wildlife. He says it's unusual that so many different kinds of species would all be dying off at the same time.

And even though leopard sharks aren't endangered, it's not a good sign that so many of them have died off in such a short time span. Losing leopard sharks from the ecosystem could have huge unintended consequences.

Luckily, Okihiro is pretty sure he knows the culprit behind the mass die-offs.


It's a small parasite called Miamiensis avidus, which is just one single cell of pure death.

zombie parasite killing sharksMiamiensis avidus, the brain-eating zombie parasite killing sharks in San Francisco Bay.

Okihiro likens it to the common amoeba. It's been appearing in huge numbers in necropsied sharks, and the method by which it possesses and kills its prey is absolutely bone-chilling — just in time for Halloween.


First, the parasite enters through its victim's nose, gnawing away in nasal canals until it bores its way into the brain and eats the brain.

zombie parasite killing sharks


Then the shark, weak and disoriented, either swims in repeated circles or beaches itself and dies.

zombie parasite killing sharks


Okihiro told NBC Bay Area that because sharks don't naturally float, the sharks that have died from this infection may have just sunk to the bottom of the seafloor without leaving a trace. So the estimated count of 2,000, which was derived simply from sharks that beached themselves or died visibly, may be far lower than the real death count.


Now that the perpetrator has been identified, Okihiro and other scientists are now figuring out a way to keep the parasite from spreading elsewhere in the Pacific Ocean.

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