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Sunday, 2 December 2012

The fruit bats, the palms and lytico-bodig

This entry is dredged from old files. It has the potential to have been overtaken, but Kymmaree made a comment that you can see in Collecting and Pressing Plants, and I am too busy right now to do a full reply, so this will have to do.


First, here is what I wrote in July 2002: note the date carefully, because there may be newer findings!

The neurological disease, lytico-bodig is found only on the island of Guam, and it is now becoming rare. It became well-known when Oliver Sacks wrote of it in his book, The Island of the Colour-blind, describing his experiences on four islands in the area of Micronesia.  (By an odd coincidence, I had been on the island of Pohnpeim helping them with their science curriculum, and transited twice through Guam, not long before Sacks went there; I am quite colour-blind; and I attended a lecture by Sacks at about that time. Sadly, I knew nothing of his observations, and he wasn't talking about that work.  You win some, you lose some)

The disease hits many of the older Chamorros, the indigenous people of Guam, and its symptoms include loss of recent memory, wasting muscles, Parkinson-like tremors or complete immobility.

Aside from the book (highly recommended for a general readership), Guam has for many years been the focus of major studies. In medical circles, though, lytico-bodig as it is called by the Chamorros, is identified as a neurological disease known as ALS-PDC, short for amyotrophic lateral sclerosis - Parkinson-dementia complex.

Under either name, it exhibits itself with symptoms and fatigues in common with Lou Gehrig's, Alzheimer disease, and Parkinson's disease. The presence of the disease in the population of the Chamorro increased at alarming rates, and then just as mysteriously, decreased. Investigations have looked at everything from the water they drink to the air they breathe, but no solid evidence has been linked to the disorders.
Another view of the same plant

At its peak, ALS affected some 400 per 100,000 Chamorro, but now that Guam's cycad-eating bats have disappeared, the rate has fallen to about 22 per 100,000. Confined to the Chamorro lytico-bodig climaxed in the 1940s when it was the main cause of adult death and today it only occurs in older adults and rarely in any individual born after 1960. There was no genetic link to the disease, nor was there any obvious infectious origin. The only known correlate seemed to be with the Chamorro diet, and it was known that the toxins of the cycad plant caused neurological disorders.
An Australian cycad with fruit

That made sense: the cycad, a primitive sort of plant, is generally toxic, but in most parts of the world, locals know how to treat and eat the seeds. And sure enough, the Chamorros knew of the plant's toxicity as well. They ate part of the cycad in the form of flour in tortillas, the plants were washed repeatedly, and the amount of toxin they were exposed to was minimal.

On the other hand, there is a Chamorro delicacy, flying fox in coconut milk, that might be to blame. The flying fox is actually a large fruit bat, with a wing span of 1.2 metres (four feet) or more, and this dish is a delicacy served on special occasions. Mostly consumed by men, the entire animal, including the fur and all the insides, are eaten during social gatherings and certain important events. Women sometimes eat the bat as well, but only the breast meat.

Earlier this year, Sacks (from the Albert Einstein College of Medicine) and Paul Cox, Director of the National Botanical Gardens in Kauai Hawaii, came up with a tantalising suggestion. The bats are known to forage on cycad seeds, which contain much higher levels of neurotoxin then the rest of the plant. According to Cox, "when the people consume the animals, the effects of the toxin could be biomagnified," leading to high enough levels of the neurotoxin for people to show signs of ALS-PDC.

Flying foxes are hard to photograph
when flying and even harder to shoot.
Further evidence: the bats were eaten in ceremonial occasions and their consumption was a core part of Chamorro custom, particularly in the villages of Umatac and Inarajan, and these villages have the highest incidences of the disease. The authors also found the flying foxes some times consume up to two and a half times their body weight per night in fruit and nectar - and that they were particularly fond of cycad seeds.

So why did the disease break out and then die away? The island was taken over by the US military after World War II and used as a military base, leading to a new economic system, disposable income, and a heavy trade in the bats. One species of flying fox has already been wiped out on the island, and another is on the verge of extinction.

By day they roost in trees and so
are very easy to shoot.
The US military is not wholly to blame: the introduction of guns for hunting has led to massive downturns in the populations of food animals on many other Pacific islands. Flying foxes remain still, hanging in trees during the day, even when people are at close enough range to have an easy shot with a small-bore rifle, so after the 1940s, a great deal more flying fox was available, but in the end, the species was hunted almost to extinction by the 1970s, and the locals were then supplied with imported bat carcases, brought from Samoa, about 18,000 of them each year, at US$35 each. Significantly, there are no indigenous cycads in Samoa.

So far, this is only a hypothesis, and work is continuing to sample the few surviving Guam flying foxes to see if the bats contain high levels of the cycad toxin. Sandra Banack an ethnobotanist at California State University in Fullerton, California is working on the issue. "This is just a start," she said in a recent interview, "Bush-meat has the potential to contain many kinds of toxic chemicals. People should be cautious eating it."


Then I wrote this in August 2003:

Lytico-bodig  is a condition that is now only encountered in elderly people on the island of Guam. It shows up as what is technically called ALS-parkinsonism dementia complex (ALS/PDC), one of the reasons why the Chamorro name lytico-bodig is also common. The Chamorro people of Guam once had an incidence rate of ALS-parkinsonism dementia complex that was 50 to 100 times higher than the rate of ALS elsewhere. The decline in the incidence of ALS/PDC among the Chamorro mirrored the decline of the population of flying foxes (a type of fruit-bat), by the 1960s and 1970s.

It seems likely that the local flying foxes were absorbing some sort of toxin that came from a plant on the island, probably one of the local cycads. The local bats were hunted almost to extinction after World War II, and replaced by bats imported from other islands which do not seem to cause the same problems. But while the disease is no longer a problem, it remains an important area of study because it offers researchers the chance to model some of those conditions, and perhaps get an insight into what is causing them.

Now fifty-year-old museum specimens of the Guamanian flying fox may shed more light on why the Chamorro people once had an extremely high incidence of lytico-bodig. At the same time, the study, supported by the ALS Association, introduces the role that biomagnification of neurotoxins might play in the development of symptoms similar to those of ALS, Parkinson disease and Alzheimer disease.

Researchers report in the August 12 (2003) issue of Neurology that skin tissues of the flying foxes contained elevated quantities of BMAA (beta-methylaminialanine, or more formally, n-methylamino-L-alanine), a non-protein amino acid that has shown to kill neurons in cell culture, and is believed to be a possible cause of ALS/PDC.

Once readily available and consumed by the Chamorro, native flying foxes in Guam are now an endangered species, so the two researchers, located at the Institute for Ethnobotany, National Tropical Botanical Garden in Kauai, Hawaii, turned to bat skin specimens from Guam now housed at the Museum of Vertebrate Zoology at the University of California at Berkeley, to measure the concentration of BMAA.

The skins contained a high concentration of BMAA - ranging from 1287 micrograms per gram, or parts per million to 7502 micrograms per gram. For comparison, the researchers also analyzed cycad plant seeds for their toxicity because they were an important part of the diets of both the flying foxes and the Chamorro. Although cycad seeds contain BMAA, the concentrations of the neurotoxin in processed cycad flour is believed to be too low to be toxic, and therefore their consumption was not associated with immediate ill effects. Compared with the high concentrations in bat skins, the concentration of BMAA in the unprocessed seeds averaged 9 micrograms per gram.

"The concentration of BMAA in these 50-year-old museum specimens suggests that the Chamorro people may have unwittingly ingested high doses of BMAA when they ate flying foxes," says Paul Alan Cox. "This appears to be a consequence of biomagnification of the toxic substances in the food chain."

Cox and Sandra Banack were building on the research hypothesis by Cox and Oliver Sacks, published in Neurology in March 2002, which theorized that the flying foxes' penchant for cycad seeds (which are toxic only in extreme doses) is what made the flying foxes toxic to humans. Earlier epidemiologic studies had raised the suspicion that the high incidence of ALS/PDC in Guam was due to the traditional foods of the region. Cox says other neurotoxic cycad molecules should now be studied to learn whether they are possible contributors to development of the disease.

In a related editorial in Neurology, Carmel Armon, from the Department of Neurology at Loma Linda University School of Medicine, Loma Linda, California, called the evidence of biomagnification of cycad-derived toxins in flying foxes "tantalizing."

He suggests it would be useful if future studies would confirm that the flying foxes in the museum are representative of the flying foxes that were consumed, adding: "The high concentration of BMAA in the museum specimens may have been the reason why these specific bats became museum exhibits." ALS/PDC research would also benefit from a look for biomagnification of suspected toxins in current ALS/PDC patients as well as in controls.

I'm not sure what has happened in the past nine years, but that gives the curious readers enough names and unusual terms to allow a tight Google search.

Over to you.

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