Acute poisoning by bracken fern (Pteridium aquilinum) in cattle in central Rio Grande do Sul, Brazil

Cases of acute poisoning by bracken fern (Pteridium aquilinum) in cattle from 10 small farms of seven municipalities of the Central Region of Rio Grande do Sul State, Brazil, were reviewed. The study encompassed 6,256 necropsies of cattle considering a 43-year period and included 15 necropsies of cattle dying from acute bracken poisoning. Morbidity and mortality were 17.9% and lethality was virtually 100%. In 40% of the farms the disease occurred in small outbreaks affecting several cattle per farm and in 60% only one bovine was affected in each farm. Main clinical signs include fever (40-42 degrees C), apathy, drooling, and hemorrhages; the latter were mainly from the gums, nostrils, and gastrointestinal tract. Multiple petechiae were observed in several mucosae and in the skin. Occasionally hematuria and blood in the milk were reported. The disease was invariably fatal after a course of approximately two days. Hematological changes included severe neutropenia, non-regenerative normocytic normochromic anemia and thrombocytopenia. Necropsy findings include hemorrhages o varying degrees in several organs and infarcts in the liver. Both hemorrhages and hepatic infarcts were confirmed histologically; clusters of bacterial rods and thrombosed vessels were associated with the infarcts. Marked bone marrow aplasia was a consistent finding in the four cases in which the marrow was evaluated.