LACK OF TOXICITY OF A NONSPORIDESMIN-PRODUCING STRAIN OF PITHOMYCES-CHARTARUM IN CELL-CULTURE AND WHEN DOSED TO LAMBS

In New Zealand the fungus Pithomyces chartarum normally produces spori desmin, a mycotoxin, which is responsible for the hepatogenous photose nsitisation disease known as facial eczema. Cultures from an isolate o f P, chartarum, which does not produce sporidesmin, were examined by c ell culture and by dosing to lambs to determine whether other toxic me tabolites were produced. Acute and long term toxicity studies were con ducted with the toxic response being assessed by weight changes, postm ortem and histological examination of tissues, blood biochemistry and haematology tests. An extract from a sporidesmin-producing isolate was highly toxic in cell culture, while extracts of the nonsporidesmin-pr oducing isolate did not cause a cytotoxic response to HEp 2 cells. Aft er dosing with a sporidesmin-producing isolate, lambs developed liver lesions and clinical signs of facial eczema. Serum biochemistry change s occurred which were consistent with sporidesmin poisoning. Lambs dos ed with the nonsporidesmin-producing isolate, at the rate of thirty ti mes the number of spores of the sporidesmin-producing isolate, showed no observable toxic effects. All organs were of normal appearance, and histological examination of tissues, blood biochemistry and haematolo gy results showed no abnormal changes. Similarly, long term dosing of extracts of the nonsporidesmin-producing isolate, at a rate equivalent to 100 000 spores/g of grass, produced no indication of a toxic respo nse. It was concluded that the nonsporidesmin-producing isolate of P, chartarum contained no toxic metabolites in significant concentration.