PLANT TOXICOSES
1.1 Pyrrolizidine alkaloid hepatotoxicosis
Pyrrolizidine alkaloid poisoning is a serious threat to livestock in many arid to semi-arid grazing areas of the world. Historically, disease has been seen in red kangaroos (Osphranter rufus) (Fowler 1983).
Between 2011 and 2013, southern hairy-nosed wombats (Lasiorhinus lati- frons) inhabiting degraded habitat in SA were identified with severe bilaterally symmetrical exudative and necro- haemorrhagic dermatitis of facial extremities and alopecia of sun-exposed dorsal and lateral body skin (Woolford et al. 2014) (Plate 19.1). Animals were in poor to emaciated body condition and sub-adults were more severely affected than adults. Pathological and clinicopathological investigations identified a toxic hepatopathy suggestive of exposure to plants containing pyrrolizidine alkaloids. Elevated hepatocellular leakage enzymes (GLDH, AST) and hepatobiliary enzymes (GGT, ALP) were noted. Bronchointerstitial pneumonia caused by Pneumocystis sp. and Emmonsia sp., small intestinal coccidiosis and periocular demodicosis were also seen in some cases. Toxicological analysis performed on faeces and GI contents found toxic pyrrolizidine alkaloids consistent with ingestion of potato weed (Heliotropeum europaeum). Although unpalatable, ingestion likely occurred because of decreased availability of preferred forages in degraded habitats and the emergence of weeds around the time of weaning of naive animals. Because of the often-close interaction between agricultural enterprises and wildlife, these findings have implications for the management of both conservation areas and agricultural land. The habitat where the affected wombats were found was previously a livestock grazing enterprise in which wombats had coexisted with livestock. Loss of preferred forage, weed overgrowth (following heavy rainfalls after a period of drought), habitat degradation soon after the land was destocked and the abandonment of land management practices are thought to have contributed to the disease in wombats. Some animals with skin lesions improved when brought into care and provided with good-quality food and supportive treatment.1.2 Chronic phalaris toxicity
Phalaris spp. (canary grasses) are perennial grasses commonly used in south-eastern Australian grazing systems. Poisoning has been reported in various grazing livestock species, associated with the ingestion of various Phalaris spp. Chronic phalaris toxicity has been reported in rednecked wallabies (Notamacropus rufogriseus) in Tas. (Grillo et al. 2015) and eastern grey kangaroos (Macropus giganteus) at three different sites in Vic. (Bacci et al. 2014). In both cases, animals showed neurological signs, including disorientation, ataxia, hypermetric gait, head tremors, hyperexcitability and collapse. Neuropathological changes include pronounced green discoloration of the grey matter that appeared microscopically as intraneuronal brown pigmentation (Bacci et al. 2014). Accumulation of α-synuclein aggregates and neuromelanin have also been recorded in brain tissues (Tayebi et al. 2019). Phalaris aquatica was present on properties where affected animals were found (Bacci et al. 2014; Grillo et al. 2015). A study by Chen et al. (2024) showed that chronic phalaris toxicity in macropods is widespread and peaks in July in Vic. They demonstrated a significant positive correlation between case count and both the abundance of eastern grey kangaroos and western grey kangaroos (M. fuliginosus) and the abundance of P. aquatica, and a significant negative correlation between annual case count and average rainfall of March and April. As incidents of CPT in macropods in Vic. has raised concern about the impacts on animal welfare and public safety, understanding these relationships will assist land and wildlife managers in predicting the risk and magnitude of CPT outbreaks in Vic.
1.3 Steroidal saponin toxicity
Multiple juvenile and adult eastern grey kangaroos presented with blindness and dermatitis in the Wagga Wagga region of NSW (Steventon et al.
2018). Affected animals exhibited photophobic behaviour, blindness, ataxia, recumbency, lethargy, ear shaking and behaviour consistent with distress or depression. The photophobia manifested as abnormal shade-seeking during the day, including finding refuge under structures frequented by people. Severely affected kangaroos were jaundiced and had elevated serum bilirubin and GGT. Blindness in affected animals was attributed to corneal oedema and inflammation. Distal extremities, including pinna and forearms, were most affected. Histological lesions included mild keratitis accompanied by moderate to severe corneal oedema and affected skin typically exhibited a moderate to severe necrotising or ulcerative dermatitis. The liver of affected animals included acicular clefts typical of steroidal saponins. The crystal-associated hepatopathy was consistent with intoxication by steroidal saponins, suggesting that affected animals had ingested sweet grass (P. gilvum) which is a recognised source of hepatogenous photosensitisation for grazing livestock (Steventon et al. 2018).1.4 Other plant toxicoses
Other plant toxicoses reported in Australian mammals are detailed in Table 19.1.
2.