Despite What You May Have Heard, Licking Frogs Does Not Cure the Flu

Amphibian skin is an interesting thing, between the chemicals secreted by the animals themselves and the microbes that thrive on their skin. Poison dart frogs, those neon cuties of the rainforest, are thusly named because their skins secrete a chemical so poisonous that the indigenous people of the Amazon hunt down these teensy frogs and rub their hunting darts on them. The skin microbiome of certain amphibians could help us figure out how to curb the fungal epidemic called chytridiomycosis that threatens tropical frogs. You’ve probably heard about dogs — and some people! — licking cane toads to obtain a hallucinogenic dose of toad venom. And now an international team of researchers reports that the skin of a common frog produces a chemical with direct virucidal action against a nasty strain of human influenza A.

The chemical is a host-defense peptide that the researchers named urumin, and it’s produced by a common South Indian frog, Hydrophylax bahuvistara. The researchers report that when they exposed human influenza A particles to urumin in the lab, the urumin latched onto the viral particles and physically destroyed them.

Electron micrograph of A) Intact flu virus particles; B) Remnants of lysed flu virus particles after incubation with urumin. Image: Holthausen, Jacob et al, 2017

It did this by seeking out a normally sheltered place on the virion’s surface. The strain of flu they were using binds to human cells using lollipop-shaped extensions jutting out from its surface. The extensions are made of a protein called hemagglutinin (HA). Different strains of the flu have different versions of the antigen on the business end of this docking stalk, but the stalk itself tends to be conserved between strains.

Influenza virions, or viral particles.

While the peptide was only active against one strain of the flu, the researchers report that it did display antiviral activity in vitro and in vivo. In addition to destroying viral particles in the Petri dish, urumin “protected naive mice from lethal influenza infection.” When administered intranasally, the peptide protected mice against a lethal dose of influenza particles.

The researchers aren’t certain of the mechanics by which this peptide destroyed the virus. They hypothesize that electrostatic interactions, like the ones that govern protein folding, are responsible for the sudden destruction. But since the HA stalk tends to be conserved between strains, if we could figure out how this peptide manages to attack just the stalk, it could be a real step toward a universal flu vaccine. Once we know what amino acid sequence enables the peptide to bind to the HA stalk, it becomes possible to use technologies like CRISPR to engineer useful peptide variants.

In the meantime, jokey articles aside, please do not attempt to treat the cold or flu by licking frogs.

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