for National Geographic News
Throughout the last century the Chamorro people of Guam suffered alarmingly high incidences of a mystery neurological illness found to be a hundred times more common than in the United States. Last year researchers suggested this sickness is linked to the tradition of feasting on the Mariana flying fox, a type of bat, which accumulates neurotoxins in its diet.
Now scientists report in the June edition of the journal Conservation Biology that the recorded increase and decrease in prevalence of the disease was closely mirrored by the rate of human consumption of these bats. The team predicts that originally dense populations of the herbivorous flying fox (Pteropus mariannus) may have once dwarfed the human population six-fold and have plummeted from more than 60,000 animals to fewer than 200 today.
"Through the consumption of cycad [seed]-fed flying foxes, the Chamorro people may have unwittingly ingested large quantities of cycad neurotoxins," says the study.
Bowl of Bat
Following World War II when Guam changed hands from Japanese to American control, researchers began to notice a higher incidence of a neurological disease similar to Lou Gehrig's, Parkinson's, and Alzheimer's. Known as amyotrophic lateral sclerosis-Parkinsonian dementia complex (ALS-PDC), or "lytico-bodig" by the Chamorro, the illness causes muscle weakness, paralysis, dementia, and death. In the village of Utamac alone, one-quarter to one-third of all deaths between 1944 and 1953 were attributed to the disorder.
Genetics, pollution, and other possible causes were all ruled out until researchers thought they'd found the key in the form of cycad seed flour, which is used traditionally to make tortillas, said Sandra Banack, ethnobotanist and study co-author at California State University in Fullerton. (Ethnobotanists study the plant-related traditions of indigenous peoples.) The disease had previously appeared to crop up more in those that lived a traditional lifestyle, she said, and it ran in families.
The seeds of cycad plants common on Guam and the surrounding Pacific islands contain high levels of chemicals toxic to the nervous system. However, that theory fell out of favor when studies showed the quantities of the chemical ingested from tortillas were suspiciously low.
That was until ethnobotanist Paul Alan Cox at the Hawaiian National Tropical Botanical Garden in Kalaheo, and other colleagues, began to wonder if cycad-seed-eating flying foxes might be involved. The bats have been especially desirable food items to the Chamorro, possibly because the tradition is one of few retained from older times before four centuries of upheaval and cultural oppression which began with Spanish colonial rule in 1565.
Served at weddings, fiestas, birthdays, and alike, the etiquette of bat-eating and preparation involves "rinsing off the outside of the animal like you would a cucumber and tossing it in boiling water," said Banack. The animals are then served whole in coconut milk and are consumed in their entirety. Meat, internal organs, fur, eyes, and wing membranes are all eaten, she said.
Last year Cox and well-known neurologist Oliver Sacks of the Albert Einstein College of Medicine in New York City reported in the journal Neurology the first evidence for a link between bat eating and the disease. Bats consume large quantities of cycad seeds, andlike some eagles, which were shown to build up levels of the pesticide DDT in fat tissueprobably accumulate the toxins to dangerous levels.
Flying Foxes Fed to Pigs
Now, Banack, Cox, and geographer Clark S. Monson of the University of Hawaii in Honolulu provide further compelling evidence for that explanation.
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