A field outbreak of suspected stachybotryotoxicosis in sheep

An outbreak of mortality in a flock of mutton merino sheep in which 109 out of 568 sheep died in the south-western Cape Province, is described. It was characterized by haemorrhagic septicaemia, anaemia, leucocytopaenia and haemorrhagic tendencies. Mortalities followed unseasonal and heavy summer rain, extended over a period of 6 months and were associated with the uninterrupted consumption of sheep cubes processed on the farm severly fungus-infested wheat, barley and rye straw for a period of at least one month. The main clinical signs occurred in two phases: an elevated body temperature, listlessness, epistaxis and intermittent haemorrhagic diarrhoea during the first phase of the outbreak, and a progressively worsening anaemia, leucocytopaenia and less severe haemorrhagic tendencies and a terminally elevated body temperature during the second phase. The predominant autopsy findings were purpuric haemorrhage on serosal and mucosal surfaces and in most of the organs, enterorrhagia and severe pulmonary congestion and oedema during the first stage; anaemia was the predominant sign during the second stage - widespread haemorrhage still occurred but was less extensive. Pasteurella haemolytica was isolated from most of the animals autopsied during the first stage. Histologically the most salient features were atrophy and necrosis of the lymphoid tissue, aplastic anaemia and a markedly impaired inflammatory response. Extensive post-natal lamb mortalities, probably due to an Escherichia coli infection precipitated by the toxicosis, occurred during the outbreak. Toxigenic strains of Stachybotrys chartarum were isolated from the wheat and barley straw. Diethyl ether extracts of the wheat straw, sheep cubes and S. chartarum culture material elicited positive skin tests in rats following intradermal injection and the presence of 12,13-epoxytrichothecenes in these extracts were confirmed by thin layer chromatography. In feeding trials sheep cubes and wheat straw caused the death of 4/4 one-day-old Pekin ducklings and weanling Wistar rats in six and nine days, respectively. This is the first description of an outbreak of disease in sheep associated with the ingestion of S. chartarum-infested food components in the Republic of South Africa.