First description of an outbreak of cattle intoxication by cyanobacteria (blue-green algae) in the South of Portugal

Abstract

A herd of 53 Angus x Charolais crossbred cows and 1 herd bull grazing a stubble field broke through an electric fence, and gained access to stagnant water from a small river (Ribeira de Oeiras). In less than 19 hours, 20 cows died and 5 were sick with clinical signs of ataxia, recumbence, abdominal distension, opisthotonus, paddling and masticatory movements, frothing at the mouth, and bloody diarrhea. The 5 sick cows later died, and the remaining 29 animals remained healthy. Clinical and pathological findings revealed the presence of hepatic and renal necrosis. In the water samples, several cyanobacterial species were identified, predominantly belonging to the toxic genera Microcystis. Altogether, these observations led to a tentative diagnosis of acute hepatoxicity caused by cyanotoxins. The diagnosis was confirmed by detection of microcystin-LR in the kidney from 1 animal. To our knowledge, this is the first report of microcystin-LR animal poisoning in Portugal.