The Bovine enzootic hematuria has been observed in numerous countries as diverse as New Zealand, Brazil, Sweden, England, Canada and Fiji, although the most affected Venezuela and Costa Rica.
Humans who consume contaminated milk from cows that feed on the fronds of Pteridium aquilinum have a high rate of stomach cancer, much higher than expected in any human population. Costa Rica ranks third worldwide in incidence and mortality from stomach cancer. The carcinogenic substances found in milk are shikimic acid, quercetin, aquilide A and above all ptaquiloside, which is considered the main toxic principle and is in highest concentration in the tender fronds. Was isolated in 1983 and its carcinogenic toxicity in laboratory animals such as rats, mice, quail, dogs, hamsters, etc. .. , in which causes malignant neoplasm of bowel, bladder, lung and lymphatic leukemia, was shown in 1984. It was also demonstrated experimentally the toxicity in cattle. When ingested is broken down into a chemical second derivative called dienone, which is the real toxic and cause direct damage to DNA and activation of oncogenes.
Cows graze in pastures where it not grows Pteridium aquilinum not have the hematuric disease and their milk is free from carcinogenic pollutants, which affects the health of humans who feed on their milk, which present a very low rate gastric cancer, similar to that expected in any human population.
In Wales, western England, where it grows in abundance Pteridium aquilinum, there has been an unusual incidence of cancer among the human population. Not being consumed as food, has blamed the contamination of well water exudative fern root and the incorporation of spores into the water in surface water systems, but has not been demonstrated any relationship.
A deep-rooted custom is padded with fronds of Pteridium aquilinum boxes with fresh oysters. In this case perhaps the danger is contamination with spores of the fern open oysters and placed on the fronds.
In countries where this fern behaves as an invasive weed, crowding out the normal grass, are studying various methods of eradication, which to date have been too costly and ineffective.
And finally in the air is a question: why such toxicity?. The answer could perhaps be the same as for the tiny poison frogs of the Amazon forests: the fern Pteridium aquilinum funnels large amounts of toxic substances in their tissues simply not be eaten, to protect itself, to eliminate by a slow and cruel form its predators, ultimately, to survive and in the light of the results, their strategy has not done anything wrong.