Background: The population genetics of parasites may be influenced by host specificity, life cycle, host geographical range, evolutionary history, and host population structure. The nematodeAspidodera raillietiinfects different marsupial and rodent hosts in the Nearctic and Neotropical regions, implying a gene flow among populations. However, niche diversification of the main hosts ofA. raillietiin superimposed areas may provide conditions for population genetic structuring within this parasite species. We examined the genetic structuring ofA. raillietiinfecting 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 175A. raillietispecimens recovered from the marsupial hostsDidelphis aurita,D. albiventris, andPhilander 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 ofD. albiventrisfrom the South region, clade III comprised parasites ofD. auritafrom the South and Southeast regions, and clade IV encompassed parasites ofD. auritaandD. albiventrisfrom the South and Southeast regions and parasites ofP. quicafrom 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 betweenA. raillietispecimens recovered from different host species, as well as from different localities, was more evident in males.Conclusion: The genetic structure ofA. raillietipopulations 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.Graphical

Environmental changes in the Brazilian Pantanal and Cerrado facilitate the spread of parasitic diseases in wildlife, with significant implications for public health owing to their zoonotic potential. This study aimed to examine the occurrence and diversity of gastrointestinal parasites in wild felids within these regions to assess their ecological and health impacts. We collected and analyzed helminth-positive samples from 27 wild felids using specific taxonomic keys. Diverse parasitic taxa were detected, including zoonotic helminths, such as Ancylostoma braziliense, Ancylostoma caninum, Ancylostoma pluridentatum, Toxocara cati, Toxocara canis, Dipylidium caninum, Taenia spp., Echinococcus spp., and Spirometra spp. Other nematodes, such as Physaloptera praeputialis and Physaloptera anomala, were identified, along with acanthocephalans from the genus Oncicola and a trematode, Neodiplostomum spp. (potentially the first record of this parasite in wild felids in the Americas). Human encroachment into natural habitats has profound effects on wild populations, influencing parasitic infection rates and patterns. This study underscores the importance of continuous monitoring and research on parasitic infections as a means of safeguarding both wildlife and human populations and highlights the role of wild felids as bioindicators of environmental health.

Cruzia tentaculatais 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 tentaculataspecimens were recovered fromDidelphis aurita,Didelphis albiventrisandPhilander quicain 9 localities. Morphological and morphometric data were investigated for phenotypic diversity among localities and hosts using multivariate discriminant analysis of principal components. Phylogenetic relationships ofC. tentaculatawere determined using maximum likelihood and Bayesian inference. The population structure was analysed by fixation indices, molecular variance analysis, Tajima'sDand Fu'sFs 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 inC.tentaculatabetween 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.

Small rodents are known hosts of various pathogens, including Hepatozoon, but until now, in Brazil, only Hepatozoon milleri has been described in these animals. In this study, liver samples and blood smears were obtained from 289 rodents belonging to 14 Cricetidae and two Muridae species that had been captured in municipalities of the states of Paraná and Rio de Janeiro. Smears were stained with Giemsa, and gametocytes were detected via microscopy in 10.72% (n = 31/289) of samples, with these individuals representing three rodent species. Significant morphometric differences were observed in gametocyte measurements in Akodon rodents. Using conventional PCR, Hepatozoon spp. 18S rDNA fragments were amplified in 24.91% (n = 72/289) of samples, with those individuals representing seven rodent species. Phylogenetic analyses clustered 41 sequences from this study into a subclade with other sequences from small mammals in Brazil, identifying four distinct haplotypes, and, for the first time, a relationship between Hepatozoon haplotype and gametocyte length was observed. Based on phylogenetic analysis, this study reinforces the trophic relationship between rodents and reptiles as a possible link in the Hepatozoon transmission cycle in South America. Furthermore, our findings expand knowledge on Hepatozoon spp. hosts, describing Oxymycterus nasutus and Oxymycterus quaestor as new host species and identifying two novel circulating haplotypes in rodents from Paraná State, southern Brazil.

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.

Praziquantel (PZQ) is currently the only drug recommended by the World Health Organization (WHO) for treating schistosomiasis, raising concerns about potential resistance. Frequent use of PZQ may reduce the genetic diversity of Schistosoma mansoni, affecting its adaptability and survival. The objective of this study was to test the impact of Praziquantel treatment and population bottlenecks on the genetic diversity of S. mansoni by experimental infection using a wild strain isolated from naturally infected rodents. Experimental infections were conducted in outbred mice, which were infected with 120 cercariae, and treated with two different doses of PZQ (3 × 150 mg/kg and 3 × 300 mg/kg) at 50, 51, and 52 days post-exposure, and necropsied 15 days later. Microsatellites and MT-CO1 were used as molecular markers. An 85.5 % reduction in parasite load (p = 0.04) was observed after 300 mg/kg PZQ treatment, with greater efficacy in male worms. MT-CO1 analysis identified two haplotypes differing by one polymorphic site, with one haplotype representing 84.2 % of the population. Low genetic differentiation was observed for MT-CO1. All seven microsatellite loci studied exhibited polymorphisms, with 3-7 alleles per locus. Praziquantel treatment caused population bottleneck, reduced genetic variability in both dosage groups: IT150 (R_ST = 0.14043, p = 0.000) and IT300 (R_ST = 0.13610, p = 0.005), and eliminated alleles with low initial frequencies. We concluded that microsatellite markers showed genetic differentiation with elimination of rare alleles, confirming the genetic bottleneck effect due to treatment with PZQ.