In the present study, Brazilian isolates of A. cantonensis were analyzed using mitochondrial COI gene sequences. This allowed evaluation of variability in A. cantonensis isolates from different geographical locations in Brazil. All sequences from Brazil were monophyletic with sequences from Asia. Tokiwa et al. (2012) , distinguished eight different haplotypes, named ac1 to ac8. Most sequences from Brazilian samples were either ac5 or ac8. Moreover, we described a new haplotype named ac9, monophyletic with Chinese haplotype ac6.
The intraspecific variation observed among the Brazilian isolates ranged from 0.8% to 6.4%. These values are in agreement with the findings of Blouin (2002) , which showed that the level of mtDNA sequence variation among nematode individuals of the same species is lower than 10%.
The data observed in this study showed that the A. cantonensis isolate from Caju (state of Rio de Janeiro) is restricted to the port area and could have entered the country through trade from Asia. The factor that might have prevented dispersal of haplotype ac9 to other places in the country is the absence of the main intermediate host, A. fulica, at the site where the rats were trapped.
Similarly, the Brazilian isolates from Pirituba (state of São Paulo), Queimados and Niterói (state of Rio de Janeiro), which correspond to haplotype ac5 from Japan, are believed to have entered through Rio de Janeiro or São Paulo also from the Asian continent. This hypothesis is also considered for the most abundant Brazilian haplotype (ac8), showing the possible spread from the arrival area to the Southeast, Northeast and North regions, probably through the giant African snail, A. fulica.
Likewise, Araujo (1967)  showed in a study on helminth fauna in Rattus norvegicus in the city of São Paulo that all rats captured were parasitized by 1 to 11 species of helminths. Interestingly, the helminth fauna lacked species of the genus Angiostrongylus. Moreover, Pessôa and Martins (1982)  reported that J.E. Alicata did not find A. cantonensis infection in rodents collected in the Brazilian state of Bahia, suggesting the recent introduction of the parasite in the country.
A. fulica has been considered a snail pest in tropical and subtropical regions where it has been introduced. In Brazil, this exotic snail was introduced in the state of Paraná in the 1980s, probably brought from Indonesia for commercial purposes that were not successful (escargot farming). The high reproductive capacity and the tendency for people to release snails into the wild are the probable reasons for the rapid invasion of this species [8, 11]. This snail is currently found in most Brazilian states. Factors such as its voracious feeding habits contribute to the extermination of the native snail fauna, reducing the available resources and increasing competition for physical space. The absence of natural pathogens also contributes to the high dispersion of these snails .
The increased presence of A. cantonensis in the country is likely a result of the rapid spread of its intermediate host, A. fulica, contributing to the dispersion of this parasite and infection of the definitive host . This phenomenon is described as one of the primary causes of the spread of eosinophilic meningoencephalitis .
The genetic variation observed among Brazilian isolates supports the hypothesis that the appearance of A. cantonensis in Brazil is a result of multiple introductions of parasite-carrying rats and the snails that act as intermediate hosts. These were likely transported on ships due to trade with Africa and Asia during the period of European colonization [8, 14] and dispersed via human transport, becoming endemic in port areas . At the present moment a phylogeographic study of A. cantonensis is essential to locate the geographical origin of these introductions, especially of haplotypes ac8 and ac9.