DIAGNOSIS
Antemortem diagnosis of NA in Australian native mammals is difficult. A presumptive diagnosis can be made based on signalment and clinical signs if other causes are ruled out. When present, haematology and serum biochemistry changes are non-specific and often reflect changes associated with other organ damage or compromise secondary to neurological dysfunction.
Systemic eosinophilia is rare, although eosinophilic pleocytosis is suggestive of NA (Vogelnest and Portas 2008). Lymphocytic pleocytosis, atypical lymphocytes and no eosinophils were seen in a western grey kangaroo (Macropus fuliginosus) with NA. Advanced imaging, such as MRI and multislice helical CT, is used in human medicine to aid diagnosis and was used in a southern hairy-nosed wombat (Lasiorhinus Iatifrons) with presumptive NA (Martin and Vogelnest 2004).Serological tests have been developed for humans and dogs, but current methods of detecting specific antigens associated with A. cantonensis are generally unreliable, having low sensitivity and specificity. ELISA and Western blot analysis detecting anti-A. cantonensis immunoglobulins (IgG) in cerebrospinal fluid show more promise in dogs and humans (Lunn et al. 2012). No serological tests are available for other species. Molecular diagnostics such and qPCR and sequencing can be used to confirm Angiostrongylus spp. in tissue and potentially CSF (Chan et al. 2015).
Necropsy and histopathology of CNS tissues are required to confirm a diagnosis of NA, although a definitive diagnosis may be missed in a proportion of cases where characteristic lesions are present without visible nematodes (Ma et al. 2013). Additionally, examination of multiple sections of the brain and spinal cord may be required to find lesions and/or nematodes. Confirmation that A. cantonensis is the causative agent relies on dissection of fresh, frozen or fixed brain or spinal cord to collect parasites for morphological examination and identification (Vogelnest and Portas 2008). Infection with A. mack- errasae should be ruled out.
Differential diagnoses for NA are toxoplasmosis, bacterial or viral meningitis/encephalitis, ABLV, cryptococcosis, toxicity (tick, organophosphate), head/spinal trauma and neoplasia.
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