CHEYENNE, Wyo. Usnic acid, a substance found in some weight-loss diet supplements, is suspected as the natural ingredient in lichens that may have caused the deaths of more than 300 elk in Wyoming in recent weeks, scientists say.
The elk ingested usnic acid by eating lichen, and some scientists theorize that the chemical was what caused the animals to weaken and collapse too helpless to eat, drink or escape predators.
After six weeks of uncertainty over what was causing the illness, researchers concluded that the culprit was tumbleweed shield lichen, which is olive-colored and shaped like a well-used scouring pad.
The lichen grows on the ground in many northern states, including Wyoming's sagebrush high country, and healthy captive elk fed the lichen developed the same fatal illness.
Researchers suspect usnic acid was the cause because it was extracted from the lichen. Also, usnic acid poisoning has been previously documented in livestock, though cattle tend to recover.
But some questions remain to be answered before scientists are willing to state a definite conclusion. For example, if usnic acid was to blame, why were the muscles of diseased elk whitish and sickly looking while the animals' livers appeared healthy? In humans, liver toxicity has been the worry.
''That's one of the reasons we don't want to chalk this up to usnic acid at this point,'' said Walt Cook, a wildlife veterinarian at Wyoming's state veterinary lab in Laramie. ''Either the usnic acid is affecting the elk differently or it's not usnic acid at all. ... There may well be other compounds in there that may be the toxic compounds.''
He said he likely will need at least a few more months to confirm a cause. But John Lehmann, president of the Wayne, Pa.-based drug information outlet DrugIntel, said it would not be surprising that usnic acid could affect elk differently than humans.
''It takes energy that's supposed to be used for constructive purposes and turns it into heat,'' he said. ''So whatever part of the animal that uses the most sugar, glucose, that's the part of the animal that's going to be affected.''
Usnic acid has anti-bacterial properties and lichen containing it have several uses in traditional medicine, including as a poultice. Put into pills, it can promote weight loss by boosting metabolism.
But side effects of usnic acid have been questioned before. In January, Food and Drug Comm-issioner Mark B. McClellan said more study is needed of three diet drugs including usnic acid. And in 2001, the Food and Drug Admin-istration asked Syntrax Innov-ations Inc. of Cape Girardeau, Mo., to stop selling Lipokinetix, a diet drug containing usnic acid, saying it was to blame for ''a number of serious liver injuries'' in some people who used the drug more than two weeks.
Lipokinetix is no longer on the market, but usnic acid still is readily available over the Internet.
''As we learn of the information and evaluate the science behind it we'll proceed accordingly,'' said Kimberly Rawlings, an FDA spokesperson.
Lehmann said, however, that the FDA does not track the number of people who may be affected by usnic acid.
''You hear about a few here and a few there related to a few marketing schemes that come to light,'' he said. ''The reason it is sporadic is partly because there is no safety monitoring of herbals.''
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