New research shows Aussie lizard bites can really hurt

Australian venom researchers have uncovered a 200-million year old secret: Australia's goannas and bearded dragons, Indonesia's giant Komodo dragon, and their iguana cousins, are more closely related to snakes than to other lizards -- and they're venomous.

An international research team led by Dr Bryan Fry, of the Australian Venom Research Unit at the University of Melbourne, and colleagues at Monash University, announced its discovery in a research paper in this week's issue of the international journal Nature.

Two years ago Fry stunned the herpetology world with his discovery that several thousand species of 'non-venomous' snakes aren't actually non-venemous -- and some supposedly harmless pet snakes are potentially capable of inflicting a lethal bite.

Previously, it was believed that only two closely related lizards -- the gila monster of the southern US arid zone and Mexico, and the closely related beaded lizards of Mexico and Guatemala -- were venomous.

But now Fry and researchers at Monash University's Venom Group, and a team of international collaborators, have shown that the newly discovered lizard venoms share a suite of peptide toxins with venomous snakes, confirming that they share a primitive, lizard-like ancestor.

Venom from the eastern bearded dragon, Pogon barbata, a water-loving visitor to suburban gardens on the east coast, contains small amounts of crotamine, one of the main peptide toxins in American rattlesnake venom.

All Australian goannas and bearded dragons are venomous -- and the extinct, 6-metre varanid Megalania prisca, the largest lizard that ever lived, may have packed up to a litre of venom in its venom glands to help subdue its megafauna prey, Fry said.

Iguanid lizards, including the iguanas of the Americas and the famed marine iguanas from the Galapagos Islands, also belong the the clade of venomous lizards.

"We've shown that these animals actually have proper venom, although it's not as toxic as taipan or death adder venom -- they're not going to kill you," Fry said.

Several of the lizard venom components are highly active, small peptides, with "completely new activity," Fry said. They include a natrurietic peptide that causes a steep drop in blood pressure, and a potent anti-coagulant -- which explains why victims of bites from large varanids like the Australia's biggest goanna, the perentie, and the Komodo dragon, cause dizziness, and the wounds bleed copiously, for long periods.

The tiny size of these peptides -- less than 4 kiloDaltons -- means they avoid immune detection, making them ideal drug candidates for applications such as treating stroke induced by blood clots, or reducing hypertension.