PATHOLOGY
Gross necropsy findings are often non-specific or absent. Nematodes may be evident in the meninges, cerebral cortex, cerebellum, brain stem or spinal cord, either grossly, particularly if in the meninges, or histologically (Figs 24.2 and 24.3).
Body condition may vary according to the chronicity of disease. Gross changes may be seen in other organs (e.g. bladder distention, lung congestion). Histological changes are variable and depend on host species, infective dose of parasites, duration of infection, larval stage of the parasites (e.g. brains of flying-foxes containing fifth-stage larvae had moderate to severe lesions while those with third-stage larvae had minimal inflammatory response [Ladds 2009]), degree of host reaction and treatment provided. Neural pathology is the result of mechanical damage and haemorrhage caused by migrating larvae and the host response to larval antigens and excretory or moulting products. The latter is usually responsible for the intense, variably eosinophilic menin- goencephalomyelitis that is often seen in Australian native mammals. The severe eosinophilic inflammation seen in eutherian mammals is not as common in marsupials (Higgins et al. 1997). A. cantonensis infection can be associated with more widespread vasculopathy and associated tissue damage in other organs. Pathology seen in various Australian mammal species has been described and is summarised in Table 24.2.Table 24.2. Summary of pathology seen in Australian mammal species with neural angiostrongyliasis
Flying-foxes
| Gross | Cloudiness, congestion or brown discoloration of meninges, cerebral cortical petechiae, nematodes on the surface of the cerebellum or brain stem, nematodes (sometimes large numbers) or parts of nematodes within the brain. |
| Histologic | Eosinophilic and granulomatous meningoencephalitis; nematode sections in brain or spinal cord, most frequently in the subarachnoid space of the cerebral sulci and/or cerebellar folds; meningitis most severe around brain stem and cerebellum, with macrophages predominating in the infiltrate, often with large numbers of lymphocytes and eosinophils, some plasma cells and occasionally multinucleated giant cells. |
Marsupials
| Gross | Congestion or haemorrhage on the ventral lumbar spinal cord, distended bladder with mucosal petechiae, haematuria, fibrin tags and nematodes on the surface of the cerebellum or brain stem beneath the meninges, red granular appearance of the leptomeninges, focal haemorrhages in the midbrain. |
| Histologic | Multifocal meningeal and parenchymal perivascular haemorrhages and severe and extensive granulomatous and eosinophilic meningoencephalitis associated with multiple nematode larvae within the brain parenchyma and along the cerebral surface beneath the meninges; extensive lumbar spinal malacia and granulomatous and eosinophilic myelitis; nematodes within the meninges of the spinal cord; caseous necrosis associated with dead nematodes; multifocal spongiosis associated with haemorrhagic areas; perivascular cuffing of lymphocytes, plasma cells and macrophages; Wallerian degeneration. |
Gordon 1992; Higgins etal. 1997; McKenzie etal.
1978; Reddacliff etal. 1999; Barrett etal. 2002; Barrett 2004; Vogelnest and Woods 2008; Ladds 2009; Ma etal. 2013; ARWH 20185.
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