Not all brown snake venoms are alike, causing antivenom concern

Researchers from The University of Queensland (UQ) have discovered that venom from northern and southern populations of eastern brown snake builds blood clots in very different ways, meaning the antivenom given to people bitten by these snakes may not be as effective as it could be. Their work has been published in the journal Toxins.

Professor Bryan Fry from UQ’s School of the Environment led a team which assessed the blood-clotting toxins in venoms from every Australian brown snake species, using a process called ‘thromboelastography’ to assess blood coagulation. This showed that eastern brown snakes from southern Australia have a ‘taipan-like’ venom that builds a strong, stable blood clot; venom from northern populations of eastern brown snake, as well as all other brown snake species, triggered fragile blood clots, but lightning fast.

“Our data shows the effect on blood of an eastern brown snake bite in northern areas and a bite in southern Australia are chalk and cheese,” Fry said. This is concerning given that Australia’s brown snake antivenom is currently produced using a pool of venom of unstated geographic origin — so if it isn’t produced from both northern and southern eastern brown snake venom, “coverage could be patchy and the antivenom efficacy could vary widely”, Fry stated.

“Clinical reports have all brown snake bite cases together, regardless of species or location, so any differences for the southern population versus all other brown snakes could be obscured,” he added.

According to Fry, the team’s next step is to “go back through hundreds of hospital charts to ascertain if there is a difference, which we can do because the southern strong-clot lineage lives where no other brown snake occurs”. They can then “re-code every reported bite by geography and tease apart the clotting patterns between the strong and weak clotting types of brown snakes”.

“We will also urgently test the available human and veterinary antivenoms to see if the differences in venom biochemistry are mirrored by variations in antivenom efficacy,” he said.

Fry’s team is also sequencing the venom genes to pinpoint the mutations responsible for the differences in northern and southern eastern brown snakes, having already shown that the geographic difference in venom effect overlays with a genetic divide within the eastern brown snake.

“Our research demonstrates how diet steers venom evolution, because the southern populations consume more reptiles than the northern populations which eat more mammals,” Fry said.

“By appreciating both the evolutionary fine-tuning and the clinical outcomes of these venoms, we can better tailor our medical responses.”

Image credit: iStock.com/Ken Griffiths