Historic priapism pegged to frog legs.

Historic priapism pegged to frog legs

Collaborators from three universities seem to have solved a 100-year-old medical mystery, linking human consumption of frog legs to cases of priapism, or painful and prolonged penile erection. The research provides the first strong evidence that frog legs indeed caused two outbreaks of priapism reported by French doctors in the second half of the 19th century. But the risk of contracting the excruciating condition from these amphibious delicacies appears extremely small.

As historians with an interest in sexual disorders know, the medical literature links two memorable accounts of priapism to possible dietary causes, both among French soldiers in North Africa. Published in 1861 and 1893, the reports describe cases of "erections douloureuses et prolongees" among soldiers who had recently eaten frog legs.

Attending physicians noted that the symptoms resembled those seen in men who had overindulged in a drug called cantharidin -- popularly known as Spanish fly -- which is extracted from a particular beetle for its purported value as an aphrodisiac. In one of the North African cases, physicians dissecting a local frog found its guts full of these beetles. Until last month, however, nobody had shown that frogs eating these beetles could accumulate large enough concentrations kf cantharidin to cause symptoms in humans who eat the frogs.

Thomas Eisner of Cornell University in Ithaca, N.Y., working with colleagues from the University of Missouri in Columbia and the University of Missouri in Columbia and the University of Michigan in Ann Arbor, has now detected such concentrations in the legs of frogs fed experimental diets of cantharidin-producing beetles.

For a few days after eating the beetles, the frogs showed cantharidin levels ranging from 25 to 50 milligrams per gram of thigh muscle, the researchers report in the December CHEMOECOLOGY. On the basis of sketchy preexisting pharmacological data, Eisner and his colleagues conclude that a meal of the cantharidin-contaminated meat could contain more than enough of the compound to cause priapism.

Gorging on these legs may lead to even more serious problems, Eisner adds. People consuming 200 to 400 grams of Spanish-fly-laden frog thighs in one meal could risk death from cantharidin poisoning, he says.

The work may finally explain what came over those unfortunate French troops, but it leaves several other questions unanswered. Why, for example, aren't frogs repulsed by cantharidin-containing beetles, which secrete the potent inflammatory compound as a defense against predator? To what extent do frogs choose these beetles as part of their normal diet, and what's the actual risk of human poisoning?

Eisner fears that most physicians today might not consider cantharidin toxicity as a cause for the priapism cases they encounter among their patients. Nonetheless, he says the lack of modern reports even hinting at a link between frog leg consumption and priapism suggests the risk is very small.

"I'm not saying, 'Watch out, don't eat frog legs' -- although I'd like to say that, because frogs are endangered all over the world," Eisner says. But the work "leaves little doubt" that the North African cases have now been solved, he maintains.

As for cantharidin's effects on the frogs themselves, little is known. Anatomically, "we didn't notice any change whatsoever" in the beetle-fed frogs, Eisner says. However, he adds, "we didn't watch to see how it might have affected their behavior."