Unknown toxin killed 34 Zoo Knoxville reptiles

May 12--Scientists have determined an unknown "toxic agent" killed 34 Zoo Knoxville reptiles on a March night seven weeks ago.

Thirty-four snakes and other reptiles, including several endangered species, died in or shortly after an "environmental event" between 5 p.m.March 21 and 8 a.m.March 22. The animals that included rattlesnakes, boas, a blue-tongued skink and a Gila monster lived in a 1,400-square-foot building, one of three in the zoo's hilltop herpetology complex.

Necropsy results released this morning by the zoo and performed at the University of Tennessee College of Veterinary Medicine found that some type of toxic agent caused the animals' deaths.

The necropsies -- autopsies on bodies of animals -- found many of the reptiles had swollen blood vessels and changes in their livers and hearts. UT veterinarians determined the combination of those findings and the sudden deaths of so many animals pointed to a toxic cause.

But what that toxin was remains a mystery. Tests could not determine the poison.

No poisons or infections were found in blood from the dead reptiles or from unaffected animals. Zoo officials also determined within days of the event the reptiles didn't die from food issues, disease, infection or predators.

But zoo officials point out that carbon monoxide, carbon dioxide and electrical shock cannot be tested for in animals' bodies after death and so can't be ruled out as potential causes. Knoxville Utilities Board tests done shortly after the snakes' deaths didn't find carbon monoxide, carbon dioxide or methane gas in their building.

Keepers found 31 snakes and lizards dead when they arrived at the zoo March 22. The other three animals, including a savu python and baby radiated tortoise, later died from their injuries.

Other dead reptiles included a forest cobra, albino Eastern diamondback rattlesnake, lined flat-tail gecko and four Western African Gaboon vipers. Members of three critically endangered species -- the Louisiana pine snake, Catalina Island rattlesnake and Aruba Island rattlesnake -- died. The surviving animals included other snakes, lizards, poisonous tree frogs and a bog turtle.

Because there's no clear cause of death, the zoo will no longer exhibit or house animals in the building where the animals lived and died.

"We had hoped for a definitive answer to what happened so we can make sure it never occurs again," said Zoo Knoxville President and CEO Lisa New. "Unfortunately, there is no clear-cut answer to this situation and therefore we will not take the risk of housing animals in this building."

After the deaths, the zoo did extensive tests of the building's air quality and its heating, air conditioning and temperature monitoring systems. Air quality tests were normal. While one thermostat malfunctioned intermittently, the building temperature monitors worked. Those monitors alert zoo staff if temperatures get too hot or too cold.

Unable to replicate what might have caused the animals' sudden deaths, zoo officials decided the safest action was to no longer use the building to house animals. It will likely be used for storage.

The zoo's reptile habitats are among its oldest. Zoo supporters are raising money to build a state-of-the-art reptile education center. Zoo officials have wanted to a new home for its reptiles for three decades.

The zoo cares for some 400 reptiles and is known internationally for its successful breeding programs for some species of snakes and tortoises.

New said that closing the building "does affect the number of animals we have on view in the short term, this will in no way impact the internationally recognized work our herpetologists do to save critically endangered reptiles. That will continue.

"If there is a positive to come from this, it is the affirmation that the conservation work we do is important to our community, and strengthens our commitment and urgency to construct a new, state-of-the-art reptile education center as part of our current capital campaign," she said.

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