THE mystery of “Cycad Island” may finally have been solved. The astonishingly high incidence of brain diseases on Guam in the western Pacific may be due to the islanders’ taste for flying foxes that feed on toxic seeds.
And it’s not just the islanders who have reason to worry. If one kind of food really causes diseases that resemble dementia, Parkinson’s and motor neuron disease, then perhaps other neurotoxins are triggering these diseases elsewhere.
Oliver Sacks highlighted the devastating epidemic of neurological diseases in Guam in his book The Island of the Color-Blind and Cycad Island. At its peak, a third of all adults in some villages had a neurological condition. Researchers suspected the local flour, which was made from the seeds of a palm-like cycad, was to blame. However, animal tests were inconclusive. Eventually they found a toxic amino acid in the seeds that caused neurological impairment when fed to monkeys. “But one would have to eat a thousand pounds of cycad seeds a month to get enough of the toxins,” says Sacks.
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Now Sacks, from the Albert Einstein College of Medicine in New York, and Paul Alan Cox, director of the National Tropical Botanical Garden in Hawaii, suggest that islanders would have consumed large enough quantities of toxins if they ate flying foxes. These animals eat twice their weight in cycad seeds every night, and the neurotoxins from the seeds could accumulate in their tissues. “If the flying foxes bio-concentrate the cycad toxins a hundredfold or more, then this would resurrect and perhaps confirm the cycad hypothesis,” says Sacks.
Cox and Sacks found that only those populations on Guam that suffered greatly from neurological disorders, such as the indigenous Chamorros, ate flying foxes. “In their traditional feast, they can consume several hundred animals,” says Cox.
The flying foxes, which numbered nearly 60,000 in the 1920s, were hunted nearly to extinction in the 1960s after the introduction of guns. This coincides with a strong peak and subsequent decline in neurological disorders in the Chamorro population. Today, the diseases seldom affect anyone born after 1960. There’s also a gender connection. Four times as many men as women suffered. “Men are far more likely to eat the animal, particularly in its entirety, than women,” says Cox.
Guns also made trade in such bush meat viable, exposing more people to the possibility of developing the disease. “We find the same thing now with parts of Africa with bush meat that’s in commercial traffic,” says Cox. “There should be a moratorium on eating commercial bush meat worldwide until the food products can be proven safe.”