November 16, 2005
Study Shows More to a Lizard Bite than a Nasty Nip
By Wendel Broere
LEIDEN, Netherlands -- More lizard families than previously believed are venomous, including several species that are popular pets, scientists said on Wednesday.
Until now, pain and swelling from lizard bites assumed to be non-venomous were attributed to the bacteria that thrive on bits of meat left between their teeth from their scavenging diet.
However, the symptoms are actually from the venom, a finding which could have implications for medical research, said Dr. Bryan Fry of the University of Melbourne, lead author of the research published online by the science journal Nature.
"The venom is the perfect knock-out punch by monitor lizards to their prey like small mammals and lizards," he told Reuters. It stops blood clotting, rapidly drops blood pressure and heightens the feeling of bite pain.
His team of international scientists isolated crotamine -- the classic venom of rattlesnakes whose bite can be fatal to humans -- in the eastern bearded dragon, a popular pet.
However, the bearded dragon's delivery system is primitive and it is present in such small amounts it would not harm a human.
Fry said Indonesia's Komodo dragon -- the world's largest lizard, weighing up to 350 lbs (160 kg) -- was also venomous.
It had previously been thought that only two families of reptiles were known to have venom systems -- advanced snakes and Helodermatid lizards.
This study demonstrates there are venom toxins in two more lizard families: monitor lizards, such as the Komodo dragon, and iguania such as the bearded dragon and green iguana, but their toxin secreting glands are smaller than those of snakes.
The study effectively doubles the number of potentially venomous reptile species to 4,600 from 2,300.
"There are so many more reptiles with venom now than we previously thought. That fact itself has massive implications for a vast array of areas, whether it be evolution, drug design and development or ecology," Fry said.
Snake toxins are already widely used in medicines to treat epilepsy, haemophilia and thrombosis. The new lizard venom toxins and their molecules present a huge unexplored resource for drug design and development, according to the researchers.
"Milking the big monitors was quite simple, just gently squeezing the glands would result in 40-50 milligrams (dry weight) of liquid venom pooling at the base of the teeth," Fry said.
This means a big Komodo dragon could have more than 200 milligrams ready to delivery at any time, he said.
Fry was anxious that lizard owners should not be unduly concerned by the findings.
"If you're dinner then the venom plays a role, but if you're human it's most likely just to make your hand throb. We don't want people to suddenly be afraid of their pets," he said.
"Nor do we want any silly laws being passed against the keeping of these lizards."