The complex taxon embraced in the Pteridium genus, popularly known as bracken fern and notorious weeds in many parts of the world, is one of the few vascular plants known to induce cancer naturally in animals. It has been known for long to be acutely toxic to livestock and sublethal chronic oral feeding of bracken fronds leads to cancerous lesions in the urinary bladder, or bovine enzootic haematuria (BEH) and ileum of cattle. Bracken poisoning has been attributed chiefly to ptaquiloside, a norsesqui-terpene which is also a potent carcinogen inducing various malignancies in laboratory animals. It is capable of alkylating uncoiled DNAbases at key proto-oncogenes of selected organs. Some human populations also eat young bracken shoots and epidemiological studies in Japan and Brazil have shown a close association between bracken consumption and cancers of the upper alimentary tract. In addition, other studies reveal that the mere presence of bracken swards represents a greater risk to die of gastric adenocarcinoma for people who live more than 20 years in such areas or are exposed in childhood. This work reviews the bracken-cancer connections established by in vitro and in vivo experiments and epidemiological studies in various parts of the world, and provides insights into the possible bridges for bracken carcinogens to reach the human diet. Also, specific points where more research is needed are highlighted.

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To explore a possible connection between specific environmental factors that might explain the high rates of stomach cancer in people living in the highlands of western Venezuela, an epidemiologic study was conducted in 2 regions of contrasting topography. The regions embrace 3 Andean states, Mérida, Táchira and Trujillo, and the vicinal lowland surrounding the Maracaibo lake basin of Zulia State. Statistical sanitary records from 1986 to 1996 comprising 5.5 million people in the study area indicated that age‐sex‐adjusted gastric cancer death rate per 100,000 people (DR) was up to 3.64 times higher in highland than lowland areas, although total cancer‐related DRs were comparable in both regions. DRs of other less frequent cancers from the upper alimentary tract [esophagous (1.18/0.99) and mouth‐throat (1.39/2.64)] showed comparable values in both regions as well as colorectal, breast, and uterus‐cervix cancers, suggesting that the stomach cancer DRs were related to geographically determined factors. Comparison of some nutrition issues, incidence of Helicobacter pylori infection in selected areas, the discovery of the bracken carcinogen ptaquiloside in milk from bracken‐fed cows, the prevalence of this plant in mountain cattle households and pasturelands and the rates of bracken‐evoked bovine enzootic hematuria led us to conclude that consumption of ptaquiloside‐contaminated milk may contribute to human gastric cancer in the Andean states of Venezuela. © 2001 Wiley‐Liss, Inc.

Tabulated data on plants in Venezuela that are toxic to livestock are presented in this chapter. Information on toxic effects is included. The extraction of compounds with insecticidal properties from these plants is mentioned.