AETIOLOGY
Angiostrongylus cantonensis is a nematode within the Superfamily Metastrongyloidea. It is a parasite of numerous Rattus spp., the greater bandicoot-rat (Bandicota indica), the grassland melomys (Melomys burtoni), fawnfooted melomys (M.
cervinipes) and the Asian house shrew (Suncus marinus) in the Asia-Pacific region (Banks and Hughes 2012; Aghazadeh et al. 2015a; Spratt 2015). It is a common parasite of the introduced black rat (Rattus rattus) and Norway rat (R. norvegicus) in south-eastern Qld and regions of Sydney in NSW (Prociv and Carlisle 2001); these species are considered the most important definitive hosts and vectors of the disease in Australia (Prociv et al. 2000). Although it has been found as far south as Jervis Bay in NSW (Stokes et al. 2007), there are no reports of A. cantonensis from western and southern parts of Australia.In Australia, another very similar species, A. mackerrasae, is found in the bush rat (R. fuscipes) in Qld and NSW and in the swamp rat (R. lutreolus) in Tas. (Bhaibu- laya 1968; Prociv et al. 2000; Stokes et al. 2007). It also occurs in the Norway rat and in mixed infections with A. cantonensis in this host in Qld, but has not been reported in the black rat (Bhaibulaya 1968). Mackie et al. (2013) described the first report of a patent infection of a species of Angiostrongylus in a non-murid host in Australia and the first report of A. mackerrasae in an accidental host, the black flying-fox (Pteropus alecto). Both Angiostrongy- lus species have a very similar life cycle and morphology, but can be differentiated using morphological criteria of the adult worms. Based on the sequencing analysis, A. mackerrasae and A. cantonensis are remarkably similar genetically and may belong to the same species, possibly as different subspecies (Chan et al. 2015). Although there is no evidence to date that A. mackerrasae is zoonotic or causes disease in any other animals (Aghazadeh et al. 2015b; Spratt 2015), it has been shown to be neurotropic in rats in the same manner as A. cantonensis (Bhaibulaya 1974). Given the similar larval migratory pathways within the hosts of these two species, it is plausible that A. mack- errasae is also neurotropic in other animals. As genetic and morphological separation of the two species is almost impossible at any stage other than fully developed adults, it is possible that nematodes in a proportion of cases of NA in humans and other animals may in fact be A. mack- errasae. Additionally, in the majority of cases of NA diagnosed at necropsy, no attempt is made to identify the species of nematode (Aghazadeh et al. 2015a). Identification can be achieved by morphological examination of adult worms. The size of the spicules of males in particular is highly diagnostic, with spicule length in A. cantonensis being approximately 1.0 mm and about twice the length of that in A. mackerrasae (Bhaibulaya 1968).
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