Lymphatic leukemia and pulmonary tumors in female Swiss mice fed bracken fern (Pteris aquilina).

Bracken fern (Pteris aquilina) mixed with a grain mixture (1:3 by weight) was fed to a group of 40 female 6-week-old Swiss mice intermittently every other week for a total experimental period of 60 weeks. Thirty-three mice survived 30 or more weeks and all developed lymphatic leukemia with multiple organ involvement. Additionally, 5 mice developed multiple pulmonary tumors. No urinary bladder or intestinal tumors, common in rats fed a similar bracken fern diet mixture, were found. No tumors were detected in 38 control mice that survived for 30 to 60 weeks while ingesting the grain mixture. Bracken fern has an inhibitory effect on myeloid tissue in cows (12, 19), causing a progressive diminution in the number of white blood cells and platelets in the peripheral blood. These alterations maximally coincide with evidence of clinical toxicity due to bracken fern. The leukocytic depression is associated with a drastic diminution in the number of polymorphonuclear leukocytes. This inversion of the ratio of neutrophils to lymphocytes suggests that bracken fern severely damages the bone marrow. However, the effect, if any, of bracken fern on the lymphoreticular tissue of rodents is not known. The objective of this study was to investigate the possible murine leukemogenic and carcinogenic effects of chronic p.o. administration of bracken fern.