A mystery illness on a Queensland island turned out to be toxocariasis. Fear swept the Aboriginal community on Great Palm Island, Qld. in 1979 when violent attacks of painful vomiting struck down 138 children and 10 adults in three weeks. All the victims were found to have enlarged livers. Many began bleeding internally or through the mucous membranes.
It took intravenous feeding and intensive care to save some of the children, who were ill for nearly a month. They were tested for every likely poison, bacterium or virus. Toxocariasis was not considered because it had never been responsible for such a sudden, explosive outbreak. Unable to find any causative organism, doctors called the illness 'the Palm Island mystery disease'.
Investigations continued, and one common factor was found: every victim had been eating mangoes. Fruit collected on the island was examined and hundreds of eggs of a Toxocara roundworm were found on the rinds. They proved to be Toxocara pteropodis - a fruit bat parasite discovered in Vanuatu but never known to have existed in Australia.
Bats of the common black flying fox species, Pteropus alecto, were captured at Townsville, 65 km to the southwest. Three out of seven suckling juveniles had the worms and were excreting them in their faeces. More infected juvenile bats were detected in Brisbane and another species, Pteropus poliocephalus was also implicated.
Mangoes were tested over a wider area, and Toxocara contamination was found among backyard fruit at Yeppoon, near Rockhampton. Commercial supplies in markets were clean, however. A fungicide treatment, required in the packing process, had removed whatever bat deposits there may have been.
Fruit bats of many species range from the subtropical coast of Western Australia, across the far north and down the east coast to northern NSW, with a huge outlying colony based in the Sydney suburb of Gordon.
Enlargement of the liver for no apparent reason, has long been noted as a common complaint of northern Aborigines. The solution to the Palm Island mystery suggests toxocariasis from bats, as well as from dogs, as a likely cause. It also indicates a possible risk to anyone eating unwashed fruit from trees that are visited by bats - especially to children who like peeling fruit with their teeth.
The worm eggs are excreted only by baby bats, clinging to their mothers and suckling while the adults feed on fruit or blossoms. After the first month or two of their lives, the juveniles cease to excrete the eggs. Since bats breed only once a year, the dangerous period is November-December.
But fruit ripening after that, if there has been no rain, could still have deposits of the long-living eggs. Washing the fruit and the hands after picking it will remove any risk.
DATE: May 1991
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