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Thursday, Aug. 29, 2002

NATURAL SELECTIONS

Fruit bats boiled in milk may be tasty, but . . .


After World War II, the Pacific island of Guam was taken over by the United States military. In the years that followed, a mysterious, debilitating and incurable brain disease struck increasing numbers of the indigenous Chamorro people, hitting the men especially hard.

The disease, known as lytico-bodig among the Chamorro and ALS-PDC among neurologists, leads to a suite of unpleasant symptoms -- the dementia often suffered by Alzheimer's patients, a slow paralysis usually associated with amyotrophic lateral sclerosis and tremors linked with Parkinson's disease. As the disease became the No. 1 killer of Chamorro adults, researchers from all over the world came to investigate. They tested everything from the purity of the water to the quality of the air, but none of them could find anything to explain the disorders.

Scientists did find that the Chamorros made tortillas with flour ground from the seeds of cycads. The large palmlike plants produce cones with fleshy seeds that contain neurotoxins, but lab rats fed on the flour failed to develop neurological disease. The islanders knew the seeds were toxic and washed them repeatedly before using them. Researchers concluded that the Chamorro were exposed to minimal amounts of toxin. The cause of the brain sickness remained unknown.

Then, suddenly, in the 1970s, cases of the disease dropped off. From occurring at more than 100 times the usual rate, cases of ALS-PDC fell to normal levels. Something happened in the '70s -- but what?

The decades-old mystery has finally been solved. Ethnobotanist Paul Cox, director of the National Tropical Botanical Garden in Kalaheo, Hawaii, and neurologist Oliver Sacks, of the Albert Einstein College of Medicine in New York (the same Sacks who wrote "Awakenings" and "The Man Who Mistook His Wife for a Hat") found that ALS-PDC had risen as commercial bat hunting increased. Giant fruit bats (also known as flying foxes) are a delicacy in Guam, and bat hunting became easier after the Americans came and guns were made readily available.

To mark an important event or to celebrate a social gathering, the Chamorro drop an entire bat (wingspan up to 1.2 meters) into a pot of boiling milk. Once the animal is cooked through, it is eaten -- all of it, fur, wings, bones and all internal organs, including the intestines. Mouthwatering stuff, to be sure, but the problem is that the bats eat large quantities of cycad seeds. The neurotoxin contained in the seeds builds up in the fat of the flying foxes.

Nevertheless, the islanders didn't know that -- they simply liked to eat bats. So they fired their American rifles freely, and bat numbers plummeted.

"Easy access to firearms increased hunter yields, which resulted in the Chamorros consuming more bat meat," said Cox. "When people consume the animals, the effects of the toxin could be biomagnified." And this, Cox and Sacks proposed in a recent issue of the journal Neurology, is the reason for the mysterious disease -- the toxin built up to levels high enough to develop signs of ALS-PDC.

It also explained why the disease occurred in men four times more often than in women: Eating bat is a male privilege. Poor women usually only get to eat the breast meat. They miss out on that tasty bat fur and gut -- and miss much of the toxins, too.

One species of flying fox is now extinct; another is on the verge. By the '70s, the Chamorro were forced to import bat meat from neighboring islands.

The ecological calamity on Guam had one happy outcome, however: Samoa and other bat-exporting islands have no indigenous cycads -- their bat meat is toxin-free. No one born after 1960 seems to have developed the disease (though many older islanders still suffer from it).

The links between the disease and the changes in the lifestyle of the Chamorro were discussed by Sandra Banack, a California State University ethnobotanist, at the American Society of Ecology meeting in Tucson, Ariz., earlier this month.

Banack interviewed the Chamorro and is examining museum specimens of flying foxes to see if they contain the cycad toxin. Her research supports the idea of Cox and Sacks that ALS-PDC cases increased when the economy changed with the arrival of the Americans after World War II.

"This is just a start," warned Banack. "Bush-meat has the potential to contain many kinds of toxic chemicals. People should be cautious eating it."

The Pacific Daily News in Guam reported that the Chamorro were still occasionally eating flying foxes caught locally. "People should not be unduly frightened if they have eaten fruit bat," Ulla-Katrina Craig, a biologist from the University of Guam, told the newspaper.

Rowan Hooper can be contacted at rowan@gol.com


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