Mass mortality of Eastern Grey Kangaroos (Macropus giganteus) associated with hepatogenous photosensitisation subsequent to ingestion of Panicum gilvum

The impact of introduced toxic plant species, to which evolutionarily naïve native mammals have little tolerance, is poorly documented but is an emerging issue in wildlife population health. Blindness associated with photosensitivity, as well as abnormal behaviours including shade seeking in domestic buildings and straying onto roads and roadside verges resulted in subsequent mass mortalities of Eastern Grey Kangaroos (Macropus giganteus), which occurred in the Wagga Wagga region of New South Wales in April 2014. Necropsy of affected cases revealed lesions indicative of dermal and corneal photosensitivity. In particular, animals presented with marked corneal oedema with a ventral to dorsal progression indicative of progressive stages of the disease. Dermal and ocular lesions were associated with cholangiohepatopathy of varying severity and chronicity and hyperbilirubinaemia. This syndrome was suspected to be a plant toxicosis resulting in hepatogenous photosensitisation. The presence of acicular clefts in hepatic portal regions suggested saponin toxicity.
An analysis of pasture proportion and species indicated a high proportion a Panicum grass initially identified as Panicum gilvum. P. gilvum has been reported to contain steroidal saponins that have been implicated in crystalline hepatopathy and cholestasis resulting in photosensitivity in livestock. UPLC/QToF mass spectrometry indicated that steroidal saponins similar to diosgenin were found in the leaves, stems and inflorescence of P. gilvum. Trace metabolites were also evaluated in livers of affected kangaroos and are as yet unidentified. Subsequent outbreaks have occurred since 2013, highlighting the importance of understanding how invasive weeds species can adversely impact populations of native mammals.