Fry and a python. Fry reassures us the blood on his hand was from a mere flesh wound. Image provided by Bryan Fry.
Despite conventional wisdom that pythons are not venomous, python owners may be surprised to learn that their favorite snakes bear traces of venom in their mouths. In a recent paper in the journal Molecular & Cellular Proteomics, researchers described how python oral glands bear the remnants of the venom-producing machinery of their venomous snake and lizard cousins. The finding has important implications for doctors who use the snake-venom detection kits to decide if a bitten person needs antivenom.
Bryan Grieg Fry at the University of Queensland in Australia and colleagues have been studying pythons and iguanas for a while because their venom production methods have not been well explored. the team has using a variety of techniques to understand the setup and mechanism of toxin production in these animals.
In previous work, Fry says, the investigators showed that powerful constricting snakes “are not primitive, as is conventionally believed, but actually highly (evolutionary) derived, with constriction as a novel form of prey capture. We had shown in other snakes, such as egg-eating sea snakes, that venom has a use-it-or-lose-it character due to the high energetic costs of making it.” For this reason, constrictors are important to study to understand how venom production has evolved in animals.
Besides being interesting from a fundamental biology standpoint, the work has practical applications. Fry explains that in Australia doctors rely on snake-venom detection kits to diagnose snake bites and figure out which antivenoms to use. “False-positives could lead to patients getting very expensive antivenom they don’t need, potentially triggering life-threatening allergies, but without the benefit of curing a snakebite, as well reducing supply for patients who actually need it,” he says.
A previous study showed that pythons cross-react in the venom-detection kits “but this curious result was dismissed as an anomaly and never thought of again,” says Fry.
In previous work, Fry says, he and his colleagues demonstrated that all snakes evolved from a common ancestor, a venomous lizard. “Snakes have various degrees of venomosity, with some being extremely advanced, such as cobras or taipans, while others have lost almost all their venom, like egg-eating sea snakes or pythons,” he explains.
Their current work in the MCP paper demonstrated that pythons pose a surprising potential source of false-positives when using sVDKs. Fry states, “We show in this paper that even though python oral glands overwhelmingly secrete mucus to swallow their large prey, there is still a trace of venom in there.”
The amount of vemon is not enough to harm a human or to kill prey, says Fry, but it’s enough “to mess up an extremely sensitive diagnostic tool.”
Fry adds that he and his colleagues are excited by finding of a low level of evolutionary ancient venom still being secreted by pythons, as the venom could contain novel. “These novel molecules therefore represent an untapped resource for biodiscovery,” notes Fry.
The investigators also delved into understanding the rictal glands, organs that are associated with venom glands. “These glands had only been investigated in a pair of studies almost 100 years ago. The secretions were shown to be highly toxic to the birds injected with it but then no more investigations were undertaken and the glands were forgotten in the sands of time,” says Fry.
In their MCP paper, the investigators showed that these glands are derived from the well-studied venom glands. This means that the venom glands aren’t the only organs involved in the secretion of venom, implicating that venom production in snakes is much more complex than previously thought.
