Visceral leishmaniasis (VL) is a tropical disease that can be fatal if acute and untreated. Diagnosis is difficult, the treatment is toxic and prophylactic vaccines do not exist. Leishmania parasites express hundreds of proteins and several of them are relevant for the host's immune system. In this context, in the present study, 10 specific T-cell epitopes from 5 parasite proteins, which were identified by antibodies in VL patients’ sera, were selected and used to construct a gene codifying the new chimeric protein called rCHI. The rCHI vaccine was developed and thoroughly evaluated for its potential effectiveness against Leishmania infantum infection. We used monophosphoryl lipid A (MPLA) and polymeric micelles (Mic) as adjuvant and/or delivery system. The results demonstrated that both rCHI/MPLA and rCHI/Mic significantly stimulate an antileishmanial Th1-type cellular response, with higher production of IFN-γ, TNF-α, IL-12 and nitrite in vaccinated animals, and this response was sustained after challenge. In addition, these mice significantly reduced the parasitism in internal organs and increased the production of IgG2a isotype antibodies. In vivo and in vitro toxicity showed that rCHI is safe for the mammalians, and the recombinant protein also induced in vitro lymphoproliferative response and production of Th1-type cytokines by human cells, which were collected from healthy subjects and treated VL patients. These data suggest rCHI plus MPLA or micelles could be considered as a vaccine candidate against VL.

Dioctophyme renale, the giant kidney worm, is a nematode related to Trichuris sp and is distributed worldwide. These parasites locate in the kidney of their definitive hosts (mainly belonging to the order Carnivora) and have an indirect life cycle with an annelid as the main intermediate host. Humans are rarely affected, but in those that are, 1 or both kidneys are destroyed. In South America, D. renale is widespread in riparian regions where changing climatic conditions, environmental degradation, and compromised sanitation are increasing the risk of distribution of this parasite, including humans. Here, we provide the descriptions of the genetic diversity of the parasite in the region by analysing 73 adult D. renale samples collected from domestic and wild carnivores. The most common hosts were (Canis lupus familiaris) and maned wolf (Chrysocyon brachyurus Fam. Canidae) among domestic and wild carnivores, respectively. This work shows the descriptions of the genetic diversity of this parasite complementing molecular methods and classical and probabilistic phylogeography. Our results strongly suggest that this parasite has been present on the continent long enough to develop local genetic variants. Also, the phylogenies show transmission between localities and bidirectional transmission between domestic and wild species. We now have new tools to understand the ecological dynamics of this parasite such as molecular markers to study its genetic diversity as well as for identification and reporting in cryptic cases.

Cestodiases, like echinococcoses and cysticercoses, represent a global health problem. Currently available anthelmintics, as benzimidazoles and praziquantel, have limited effectiveness against these cestodiases, creating a demand for the identification of new and more effective drugs. Here, the potential of statins (simvastatin and fluvastatin), for repositioning as novel anthelmintic is explored. Statins are inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, a main enzyme in the mevalonate pathway, which is vital for the synthesis of non-steroidal isoprenoids and the maintenance of normal cell functioning. A survey for HMG-CoA reductase encoding genes showed that they are present in a single copy in the genomes of parasitic helminths and their mammal hosts. Sequence alignments and phylogenetic analyses showed 20–95% overall identities among ortholog HMG-CoA reductases, with special conservation of their catalytic domains. The HMG-CoA reductase 3D-structure was predicted for orthologs from 3 cestodes of medical importance (Echinococcus multilocularis, Echinococcus granulosus sensu lato, and Taenia solium), and from a model cestode species (Mesocestoides corti). Molecular docking between cestode HMG-CoA reductase orthologs with simvastatin demonstrated that the Arg, Ser, Lys, and Glu residues in conserved positions of the active site interact with this drug, similarly to the interactions predicted for the human reference ortholog enzyme. Furthermore, in vitro assays demonstrated that simvastatin produced a significant reduction of M. corti viability, being able to reduce 100% of parasite viability at 150 μm. Fluvastatin was also assessed showing a lower, although significant anthelmintic effect. The predicted overall structures and interactions together with in vitro assays suggest that cestodes HMG-CoA reductases are inhibited by simvastatin, being a potential therapeutic target for the repurposing of simvastatin as anthelmintic drug. Furthermore, these results pave the way for the in vivo evaluation of the potential effects of simvastatin on cestode larvae.

Elevated levels of IL-6 in plasma are associated with the severity of visceral leishmaniasis (VL). The clinical manifestations of VL vary among patients, influenced by host factors and the virulence of the Leishmania infantum parasite. Considering that severe VL may result from an exaggerated inflammatory response, this study investigated whether IL-6 could serve as a biomarker to identify pro-inflammatory virulence factors. We conducted a genome-wide association study (GWAS) analysis on L. infantum isolates from patients with VL, whose IL-6 concentrations were measured. The analysis revealed that the relationship between IL-6 levels and clinical outcomes (survival vs mortality) had an area under the curve (AUC) of 0.67 (95% CI 0.52–0.81). A cut-off of 391.7 pg mL−1 for IL-6 was established to conduct a logistic regression analysis. We identified 10 029 single nucleotide variants (SNVs) across 62 genomes, resulting in 6,948 SNVs after filtering, of which 6,341 are located in protein-coding regions. The association analysis with PLINK identified 722 variants, of which 35 showed significant associations, with odds ratios ≥3.3, primarily in coding regions. These findings demonstrate that IL-6 levels tended to be associated with the fatal outcome of VL and highlight 35 novel genetic variants that could serve as potential biomarkers for prognosis. Further research into the biological role of these variants may lead to new therapeutic targets and improve the clinical management of VL, especially in identifying high-risk patients.

Neurocysticercosis is a poorly understood infection of the central nervous system with Taenia solium larva, and the treatment often fails to kill all the parasitic larva. Most research on this infection has used patient-level data, looking at summaries of the encysted parasitic cysticercus burden. Cyst-level analysis is needed to identify factors that impact individual cyst trajectories and how that may vary based on characteristics of the patient, infection and cyst being followed. We disaggregated data on 221 cysts from 117 patients who participated in a trial evaluating the impact of albendazole treatment to identify factors that impact cyst evolution over time from the active to the degenerating and calcified phases, and eventual resolution. We found that having calcified cysts at baseline was associated with a faster rate of transition from the degenerative phase to calcified phase or resolution. Age and sex were not associated with cyst evolution in the main effect analysis, but after stratifying on treatment we found that the direction of some associations by patient age and sex was reversed for patients in the albendazole arm compared to those in the placebo arm. These findings suggest that differences in host immune response by sex and age as well as by past exposure, potentially indicated by having calcified cysts together with active cysts at baseline, are important to cyst evolution and may be modified by treatment. Future research is needed to assess if these differences suggest distinct treatment recommendations.

Neurocysticercosis (NCC) is a neglected parasitic disease that causes neurological symptoms. However, little is known about the long-term impact of this infection on health. We contacted participants from a randomized controlled trial on albendazole treatment for NCC in Ecuador 12 years after trial completion (14–16 years after NCC diagnosis) about their long-term health. We described the symptoms experienced post-trial and investigated if albendazole treatment, the presence of calcified NC cysts, and cysts in extraparenchymal locations at last imaging predicted symptoms. All analyses were standardized by adjusting for participant age and sex. In the 12 years post-trial, 52.1% reported some health problem, with 48.9% reporting neurological symptoms such as seizures (16.6% of participants) and headaches (26.6% of participants). At the end of the trial, 11 participants had complete NCC cyst resolution, of whom 3 (27.3%) reported seizures and 1 (9.1%) reported headaches post-trial. Twenty-four participants had only calcified cysts (residual calcification sometimes left after the parasite dies) by trial end, of whom 8 (33.3%) reported seizures and 9 (37.5%) headaches post-trial. None of the predictors examined were significantly associated with long-term symptoms. A high proportion of people diagnosed with NCC continue experiencing symptoms years after treatment, and while slightly fewer people experienced continued symptoms in the albendazole group, the difference was not statistically significant. Eleven participants with no live parasites at last imaging (8 with residual calcifications) had seizures post-trial, which may be unprovoked and an indication of epilepsy risk. Research is urgently needed to improve NCC treatment to mitigate long-term outcomes.

The objective of this study was to assess the potential role of aquatic biofilms as natural reservoirs for Blastocystis. For this purpose, surface water (n = 4) and biofilm samples (n = 8) were collected from a stream nearby an urban area characterized by limited sanitation infrastructure and a high prevalence of Blastocystis in humans. Blastocystis cysts were detected in three of the four water samples and seven of the eight biofilm samples using fluorescence microscopy. Furthermore, viable cysts were identified exclusively in biofilm samples (five of the eight), while no live cysts were detected in water samples. These findings indicate that aquatic biofilms provide a habitat where Blastocystis cysts can adhere and remain viable, potentially contributing to their environmental accumulation. In addition, molecular characterization of the five isolates identified subtypes ST8 (allele 21) and ST3 (allele 36). This study is the first to report the detection and identification of viable Blastocystis subtypes in aquatic biofilms. The analysis of biofilms by fluorescence microscopy, as demonstrated here, offers a promising approach for monitoring Blastocystis and could serve as an alternative to traditional water sampling methods.

Parasites of the Leishmania species have been observed to infect macrophages and thereby modulate the host microbicidal responses, resulting in a wide spectrum of diseases. A comprehensive experimental mapping of the relationship between the double-stranded RNA protein kinase R (PKR) and NF-κB pathways in the outcome of the infection was conducted in an effort to improve the understanding of the biology associated with the parasites–host cell interaction. The results showed that in the absence of PKR and Type I Interferon (IFN) signalling, L. major infection was enhanced. The levels of PKR and gene promoter activation were evaluated. The results showed that infection did not induce PKR expression by inhibiting the phosphorylation of STAT1 and subsequent binding in the PKR promoter. However, infection induced PKR phosphorylation but did not prevent subsequent signalling through this pathway. To address the role of activation of these signalling, the induction of PKR-dependent gene expression was examined. Activation of the classical p65/p50 dimer was found to be dependent on the PKR in the L. major infection, which was essential for the induction of iNOS, IFNβ and tumour necrosis factor expression. In addition, macrophages treated with nuclear factor-kB inhibitors were more susceptible to infection. Furthermore, translocation of the p65/p50 to the promoters of these genes increased in a PKR-dependent manner. Collectively, these results suggest that macrophages retain their ability to induce important downstream effectors in PKR signalling. These effectors contribute to protection in pathogenesis, reducing parasite proliferation and regulating the inflammatory genes that, consequently, modulate the activation state of macrophages during infection.

Plasmodium simium, a parasite of platyrrhine monkeys, is known to cause human malaria outbreaks in Southeast Brazil. It has been hypothesized that, upon the introduction of Plasmodium vivax into the Americas at the time of the European colonization, the human parasite adapted to neotropical anophelines of the Kerteszia subgenus and to local monkeys, along the Atlantic coast of Brazil, to give rise to a sister species, P. simium. Here, to obtain new insights into the origins and adaptation of P. simium to new hosts, we analysed whole-genome sequence (WGS) data from 31 P. simium isolates together with a global sequence dataset of 1086 P. vivax isolates. Population genomic analyses revealed that P. simium comprises a discrete parasite lineage with greatest genetic similarity to P. vivax populations from Latin America – especially those from the Amazon Basin of Brazil – and to ancient European P. vivax isolates, consistent with Brazil as the most likely birthplace of the species. We show that P. simium displays half the amount of nucleotide diversity of P. vivax from Latin America, as expected from its recent origin. We identified pairs of sympatric P. simium isolates from monkeys and from humans as closely related as meiotic half-siblings, revealing ongoing zoonotic transmission of P. simium. Most critically, we show that P. simium currently causes most, and possibly all, malarial infections usually attributed to P. vivax along the Serra do Mar Mountain Range of Southeast Brazil.

Toxoplasmosis, caused by the obligate intracellular parasite Toxoplasma gondii, is one of the most prevalent zoonotic parasitic infections worldwide. When acquired during pregnancy, T. gondii can be transmitted to the fetus, with clinical outcomes influenced by gestational age at time of infection and the parasite’s genotype. Prenatal screening enables the detection of maternal seroconversion and offers a critical window for intervention. In Uruguay, despite mandatory serological screening during pregnancy, national data on T. gondii seroprevalence and maternal seroconversion have not been updated in two decades. In addition, the genetic diversity of local strains remains poorly characterized. In this study, we analysed publicly available serological data from pregnant individuals attending Uruguay’s largest public maternity hospital between 2019 and 2023. We found that seroprevalence has modestly declined from 50% (reported in 1998) to 45.5%, with a congenital transmission rate of 0.58%. Clinical analysis of affected newborns revealed chorioretinitis as the predominant manifestation. To investigate parasite diversity, we performed genotyping of T. gondii strains using in silico PCR-RFLP following molecular detection. Our findings revealed substantial genetic diversity, including novel allele combinations not previously described in the region. These results highlight both the continued public health burden and the evolving genetic landscape of T. gondii in Uruguay. Our findings underscore the need to strengthen surveillance and prevention strategies for congenital toxoplasmosis in South America.

Common peccaries (Tayassu pecari), wild boars (Sus scrofa) and collared peccaries (Dicotyles tajacu) are species that have gained attention in Brazil because of their close relationship with human beings, their influence on the environment and the parasitic fauna they host, which is common in free-ranging animals. In this study, we obtained the carcasses S. scrofa (n = 4), T. pecari (n = 12) and D. tajacu (n = 1) that were killed by hunting (only wild boars), or by being run over or burned. The animals were necropsied and searched for parasites. The parasites found in the gastrointestinal tract were fixed in ethanol for morphological identification. The parasites identified were Ascaris suum, Monodontus rarus, Monodontus semicircularis, Strongyloides spp., Lagochilascaris minor, Eucyathostomum dentatum, Oligacanthorhynchus major and Ascarops strongylina. In addition to observing the occurrence of different species of parasites in tayassuids and suids, we also aimed to raise awareness among the population about the dangers of consuming these animals, as well as the importance of ecological relationships for the propagation of parasitic fauna. Our results indicate that parasites are host switching, possibly related to the adaptation of L. minor and M. rarus.