Helminth community of Nectomys squamipes naturally infected by Schistosoma mansoni in an endemic area in Brazil: A comparison of 22 years apart.

The municipality of Sumidouro in the state of Rio de Janeiro, southeastern Brazil, is considered an area with low endemicity of Schistosoma mansoni. In this municipality, the wild water rat Nectomys squamipes is a wild reservoir of S. mansoni. A helminth community survey was carried out on N. squamipes populations in Sumidouro from 1997 to 1999. In the present study, we compared the helminth fauna and the helminth community structure of N. squamipes with a recent survey after a 22-year time interval, considering that the prevalence of S. mansoni infection in humans remained stable and that the area showed the same environmental characteristics. Seventy-three host specimens of N. squamipes collected between 1997 and 1999 and 21 specimens collected in 2021 were analyzed in this study. Seven helminth species were found in each collection period. The nematode Syphacia evaginata was recorded for the first time in N. squamipes in 2021. Syphacia venteli was the most abundant species in both periods and the most prevalent in 2021. During the period from 1997 to 1999, the most prevalent species was Hassalstrongylus epsilon. Significant differences in prevalence and abundance in relation to host sex were observed only for S. mansoni in 1997-1999. Significant differences in the abundance of the helminth species over time were observed only in Physaloptera bispiculata. Hassalstrongylus epsilon, S. venteli and S. mansoni were the dominant species in both periods. Litomosoides chagasfilhoi, Echinostoma paraensei paraensei and P. bispiculata became dominant, codominant and subordinate, respectively, over time. In conclusion, the helminth community of N. squamipes remained stable, with similar species richness, prevalence and abundance values and low beta-diversity over time. The occurrence of S. mansoni in the water rat has remained stable for decades, highlighting its importance for schistosomiasis control.

Population genetic structure and morphological diversity of Cruzia tentaculata (Nematoda: Ascaridida), a parasite of marsupials (Didelphinae), along the Atlantic Forest on the eastern coast of South America.

Cruzia tentaculata is a helminth parasite of marsupials and has a wide geographic distribution from Mexico to Argentina. The aim of this study was to analyse the genetic population structure of this nematode along the Atlantic Forest biome. Cruzia tentaculata specimens were recovered from Didelphis aurita, Didelphis albiventris and Philander quica in 9 localities. Morphological and morphometric data were investigated for phenotypic diversity among localities and hosts using multivariate discriminant analysis of principal components. Phylogenetic relationships of C. tentaculata were determined using maximum likelihood and Bayesian inference. The population structure was analysed by fixation indices, molecular variance analysis, Tajima's D and Fu's Fs neutrality tests, Mantel tests and Bayesian clustering analysis. A higher significant morphometric difference for males was observed between localities. In the haplogroup networks, 2 groups were recovered, separating locations from the north and from the south/southeast. The morphometric variation in C. tentaculata between different localities was compatible with this north and southeast/south pattern, suggesting adaptation to different ecological conditions. Population genetic analyses suggested a pattern of evolutionary processes driven by Pleistocene glacial refugia in the northeast and southeast of the Atlantic Forest based on the distribution of genetic diversity.

Population genetic structure and phenotypic diversity of Aspidodera raillieti (Nematoda: Heterakoidea), a parasite of Didelphini marsupials in Brazil's South and Southeast Atlantic Forest.

BACKGROUND: The population genetics of parasites may be influenced by host specificity, life cycle, host geographical range, evolutionary history, and host population structure. The nematode Aspidodera raillieti infects different marsupial and rodent hosts in the Nearctic and Neotropical regions, implying a gene flow among populations. However, niche diversification of the main hosts of A. raillieti in superimposed areas may provide conditions for population genetic structuring within this parasite species. We examined the genetic structuring of A. raillieti infecting three marsupial species co-occurring along the South and Southeast Brazilian Atlantic Forest, a hotspot of biodiversity. METHODS: We employed morphometric analyses and partial mitochondrial cytochrome c oxidase I gene sequences (MT-CO1) to characterize populations via phylogenetic and phylogeographic analyses. RESULTS: Among 175 A. raillieti specimens recovered from the marsupial hosts Didelphis aurita, D. albiventris, and Philander quica, we identified 99 MT-CO1 haplotypes forming four haplogroups and four clades in networks and phylogenetic trees, respectively. Clades I and II encompassed parasites of D. albiventris from the South region, clade III comprised parasites of D. aurita from the South and Southeast regions, and clade IV encompassed parasites of D. aurita and D. albiventris from the South and Southeast regions and parasites of P. quica from the South region. High genetic differentiation between clades, with a high fixation index and greater genetic variation in the analysis of molecular variance (AMOVA), indicated low gene flow between clades. Haplotypes shared among host species revealed a lack of host specificity. A significant correlation in the Mantel test suggested parasite isolation by distance, while there was no evidence of geographical structure between populations. Negative neutrality test values for clades III and IV suggested recent population expansion. Morphometric differentiation between A. raillieti specimens recovered from different host species, as well as from different localities, was more evident in males. CONCLUSION: The genetic structure of A. raillieti populations in the South and Southeast Atlantic Forest resulted from historical events rather than from current geographical distribution or host specificity. We also demonstrate morphometric variation associated with host species and localities, suggesting phenotypic plasticity to host attributes and to spatial variables.