Researchers Suspect Bats May be Source of Brain Ailment

Scientists have long sought to understand a horrific brain disease that once devastated the native people of Guam--Lou Gehrig’s, Alzheimer’s and Parkinson’s symptoms rolled into one.

Now two researchers have uncovered clues that suggest a Chamorro dietary tradition--eating a type of bat that feeds on neurotoxic plants--might be behind the mystery illness.

It’s circumstantial evidence so far. But if the new theory is proved right, it could be more than another dismal discovery that diet can wreck the human brain. Understanding the Guam disease may help uncover novel ways to treat regular Lou Gehrig’s, Alzheimer’s or Parkinson’s diseases.

The theory, published recently in the journal Neurology, turns on the principle that changing economies can have an impact on disease. The brain disease peaked after World War II brought guns and cash to Guam, spurring commercial hunting until the bats neared extinction--and then the human disease in turn rapidly waned, said ethnobotanist Paul Alan Cox, who studies how indigenous people relate to their environment.

“This is very good news, of course, for the Chamorrons ... but neuropathologists thought they were losing the opportunity to understand the potential linkage” between the three diseases, said Cox, director of the National Tropical Botanical Garden in Hawaii. He co-wrote the article with neurologist Oliver Sacks of New York’s Albert Einstein College of Medicine.

Their hypothesis is “very interesting,” said Diane Murphy, chief of neurodegenerative research at the National Institutes of Health. “Anything that sheds light on the pathological process in that disease potentially gives you places you could intervene with therapeutics.”

The Chamorro disease is a mix of the slow paralysis of Lou Gehrig’s disease (known medically as ALS), the tremors of Parkinson’s, and dementia. Dubbed ALS-PDC, it occurred at rates more than a hundred times greater than regular ALS elsewhere, and was almost completely confined to Chamorro people who followed traditional cultural practices.

Theories abounded. Water contamination and lack of nutrients were ruled out. No suspicious genes have been found.

The leading theory turned on cycads, a plant found throughout the tropics whose seeds native populations have long known were poisonous. The Chamorro repeatedly washed the seeds to detoxify them and then mashed them into flour. Toxicologist Peter Spencer of Oregon Health and Science University says they still got enough toxin to build up over time. But Cox and NIH’s Murphy say animal studies failed to prove that flour alone was the culprit.

Cox’s theory is biomagnification: maybe people became ill by eating large bats that ate lots of toxin and stored it in their fat. A single two-pound bat can eat up to 2 1/2 times its weight a night in plants, he said.

Bat consumption had been largely ceremonial until commercial hunting began after World War II, Cox said. Then a bat population once estimated at 60,000 began to plummet. By the 1970s, one Guam species was extinct and the remaining one was endangered. Guam began importing bat meat from Samoa--where there are no cycads, Cox said.

Rates of ALS-PDC mirrored the change, he argued: In 1956, there were 308 cases of the brain disease per 100,000 people, but just 22 cases per 100,000 by 1985. Today, no one born after 1960 seems to get it, and men--who traditionally ate more bat--got ill more than women, he said.

Spencer, author of the cycad flour theory, is skeptical. “It would be surprising if consumption of such a delicacy proved to be a more important source of exposure to cycad toxins than what was formerly daily use” of the flour.

But Cox says that mercury-tainted fish, PCB-tainted whale meat and mad cow disease-tainted beef have all caused brain diseases--and that it’s important to know if bats eating a natural toxin could too.