Effect of praziquantel on adult Echinostoma paraensei worms in experimentally infected mice

A new cryptic species of Echinostoma (Trematoda: Echinostomatidae) closely related to Echinostoma paraensei found in Brazil

Echinostoma paraensei, described in Brazil at the end of the 1960s and used as a biological model for a range of studies, belongs to the ‘revolutum’ complex of Echinostoma comprising species with 37 collar spines. However, molecular data are available only for a few isolates maintained under laboratory conditions, with molecular prospecting based on specimens originating from naturally infected hosts virtually lacking. The present study describes Echinostoma maldonadoi Valadão, Alves & Pinto n. sp., a species cryptically related to E. paraensei found in Brazil. Larval stages (cercariae, metacercariae and rediae) of the new species were found in the physid snail Stenophysa marmorata in the State of Minas Gerais, Brazil, the same geographical area where E. paraensei was originally described. Adult parasites obtained experimentally in Meriones unguiculatus were used for morphological (optical microscopy) and molecular [28S, internal transcribed spacer (ITS), nad1 and cox1] characterization. The morphology of larval and adult parasites (most notable the small-sized dorsal spines in the head collar), associated with low (0–0.1%) molecular divergence for 28S gene or ITS region, and only moderate divergence for the mitochondrial cox1 gene (3.83%), might suggest that the newly collected specimens should be assigned to E. paraensei. However, higher genetic divergence (6.16–6.39%) was found in the mitochondrial nad1, revealing that it is a genetically distinct, cryptic lineage. In the most informative phylogenetic reconstruction, based on nad1, E. maldonadoi n. sp. exhibited a strongly supported sister relationship with E. paraensei, which may indicate a very recent speciation event giving rise to these 2 species.

Zygocotyle lunata as a model for in vivo screening of anthelmintic activity against paramphistomes: Evaluation of efficacy of praziquantel, albendazole and closantel in experimentally infected mice

Paramphistomes are important parasites in veterinary medicine. There are few anthelmintic drugs available against them. The development of new drugs is urgently needed and this process can be accelerated through the development of rodent models for in vivo testing. Among the few paramphistomes that develop in rodents is the caecal fluke Zygocotyle lunata, a species with which several biological studies have been performed over several decades. Nevertheless, its use as a model for evaluation of anthelmintic drugs had not yet been evaluated. In the present study, we evaluated the efficacy of praziquantel (PZQ 300 mg/kg 5x), albendazole (ABZ 200 mg/kg 5x) and closantel (CLO 50 mg/kg single dose, 50 mg/kg 3x and 25 mg/kg 3x) for treatment of mice experimentally infected with Z. lunata. The animals were infected with 20 metacercariae of the parasite and were treated 30 days post-infection. Untreated groups were maintained as controls. Seven days after the treatments, the animals were euthanized for recovery and counting of parasites. We found that PZQ and ABZ, at the dosages and therapeutic schedule employed here, did not cause significant alterations in worm burden [worm counts 16.0 ± 2.8 (13-19), 17.6 ± 2.1 (14-19) and 16.2 ± 1.9 (13-18) (p = 0.51) in PZQ, ALB and control, respectively]. CLO 50 mg/kg in a single dose caused significant reduction in the number of parasites [treated: 1.8 ± 0.9 (1-3); control: 15.6 ± 2.5 (12-19)], although it did not result in complete elimination of the parasites in any animal. Despite the fact that three doses of CLO 50 mg/kg or CLO 25 mg/kg caused complete elimination of the parasites in most surviving animals, there was significant host mortality. In general, results here obtained are concordant with those of studies performed on ruminant paramphistomes. Given that Z. lunata can be maintained in laboratory rodents, it is a suitable model for screening anthelmintic drugs against paramphistomes.

Changes in hemocytes of Biomphalaria glabrata infected with Echinostoma paraensei and exposed to glyphosate-based herbicide

The immune system of snails is highly sensitive to pollutants, which can suppress its immune response. We investigated the effects of exposure to the glyphosate-based herbicide Roundup® Original on the snail Biomphalaria glabrata infected by the platyhelminth Echinostoma paraensei by evaluating changes in the snail's internal defense system. Four cohorts were studied: control group, infected snails, snails treated with Roundup®, and snails infected and treated with Roundup®. The hemocyte viability was assessed, morphological differentiation of cells was observed and flow cytometry was performed to determine the morphology, viability and the lectin expression profiles. The frequencies of dead hemocytes were lower in the infected group and higher in both pesticide treated groups. Three cell types were identified: blast-like cells, hyalinocytes and granulocytes. The highest number of all types of hemocytes, as well as the highest number of dead cells, were observed in the infected, pesticide-treated group. The association between infection and herbicide exposure greatly increased the frequency of dead hemocytes, suggesting that this condition impairs the internal defense system of B. glabrata making the snails more vulnerable to parasitic infections.

Morphological effects on helminth parasites caused by herbicide under experimental conditions

Helminth parasites have been studied as potential accumulators for different pollutants. Echinostoma paraensei is a foodborne trematode whose vertebrate host, the rodent Nectomys squamipes, is naturally exposed to environmental pesticides. However, little information exists regarding the pesticide's effects on helminths. This study investigated the morphological effects on the trematode, E. paraensei, after experimental Roundup® herbicide exposure, in concentrations below those recommended for agricultural use. After two hours of exposure, scanning electron microscopy (SEM) showed changes to the tegument, such as furrowing, shrinkage, peeling, spines loss on the peristomic collar, and histopathological evidence of altered cells in the cecum and acinus vitelline glands with vacuoles and structural changes to the muscular layers. Glycidic content was decreased, primarily in the connective tissue. As E. paraensei is an intestinal parasite of the semi-aquatic wild rodent, N. squamipes, it is predisposed to pesticide exposure resulting from agricultural practices. Therefore, we emphasize the need to evaluate its impact on helminth parasites, due to their pivotal role in regulating host populations.

In vivo and in vitro effects of the herbicide Roundup(®) on developmental stages of the trematode Echinostoma paraensei

The exposure of wildlife and humans to toxic residues of Roundup(®) through agricultural practices or the food chain has been reported since the herbicide was found contaminating rivers. Glyphosate, N-(phosphonomethyl)glycine acid, is a nonselective post-emergent herbicide and is formulated as an isopropylamine salt with the surfactant taloamine polyethoxylate (POEA) representing the commercial formulation of Roundup(®). There is little knowledge about the effects of the herbicide on helminth parasites, particularly those whose life cycle is related to water bodies. Here we investigated the effects of the Roundup(®) on the food-borne trematode Echinostoma paraensei in experimental conditions using different developmental stages (eggs, miracidia, cercariae, metacercariae, newly excysted larvae (NEL), helminths at seven days and helminths at fourteen days). Three different herbicide concentrations were tested based on concentrations typically applied in the field: 225, 450 and 900 mg/L. Specimens were analyzed in vitro for hatching miracidia, mortality and excystment rate of metacercariae and in vivo for parasitic load and egg production. There was a significant difference in the hatching miracidia rate only for the newly embryonated eggs. The mortality of specimens and excystment rate of metacercariae were concentration-dependent. There was a significant difference in the miracidia mortality with respect to concentration until 56.3 mg/L. The same effect was observed for cercariae, and mortality was observed from 15 min onwards at concentrations of 225-900 mg/L. At low concentrations, mortality was detected after 30 min. The effects of the herbicide concentration on NEL and on helminths at seven and fourteen days showed a significant difference after 24 h. There was no significant difference in parasitic load and egg production after infection of rodents with exposed metacercariae. All developmental stages of the trematode E. paraensei were affected by Roundup(®) exposure under experimental conditions. These results suggest that dynamics of transmission of the trematode could be affected in the natural environments. The study also reinforces the usefulness of this trematode as a good model organism to test pesticides regarding human and environmental health.

Effect of Praziquantel on the Tegument and Digestive Epithelium Ultrastructure of Brachylaima sp. Metacercariae Parasitizing the Edible Land Snail Cornu aspersum

The edible land snail Cornu aspersum (Pulmonata: Stylommatophora) acts as second intermediate host in the cycle of Brachylaima sp. trematode, harboring free metacercariae in its kidney. The ingestion of undercooked infected snails by humans allows metacercariae to develop to adult stage in the intestine, causing brachylaimiasis. Praziquantel (PZQ) is the drug of choice to treat trematodiasis and it is effective against Brachylaima sp. metacercariae. The objective of this work was to assess, by transmission electron microscopy (TEM), the ultrastructural changes produced on the tegument and gastrodermis of the Brachylaima metacercariae recovered from C. aspersum treated with PZQ in comparison with untreated ones. Snails naturally infected by Brachylaima sp. metacercariae were treated by PZQ both individually and in groups. Metacercariae recovered from treated and control snails were processed for TEM. The tegument of untreated metacercariae was covered by a regular and thick glycocalyx. The syncytial epithelium contained abundant T2 secretory bodies appearing as membrane-bound biconcave disk-vesicles with high electron-dense and uniform content. The T2 secretory bodies located along the external area of the syncytium were mainly arranged at right angles to the apical plasma membrane. In treated metacercariae, the content of the T2 secretory bodies appeared altered, degenerating from high to low electron density, losing its uniform appearance and forming high electron-dense accumulations scattered around the periphery of the vesicle and separated by low electron-dense spaces. The presence of clusters was detectable in the central area. The characteristic arrangement of the T2 secretory bodies observed in untreated metacercariae was lost in treated ones. Vesicles near the apical area of the tegument no longer maintained their arrangement perpendicular to the apical plasma membrane. The characteristic arrangement of T2 secretory bodies and mitochondria was lost. The T2 secretory bodies were also found altered in the tegumental cell bodies, suggesting that the alterations started at the production stage. Mitochondria were severely degenerated and located in the apical area of the tegument. The digestive system displayed a strong contraction, which included the disappearance of the intracecal lumen.

A simple and efficient method to observe internal structures of helminths by scanning electron microscopy

Morphological studies of helminths by scanning electron microscopy are generally limited to the external topography of the organisms. In this work, we present a simple technique using ethanol as a cryoprotectant without postfixation in osmium tetroxide that allows for observation of the inner organization of helminths and preserves cellular structures. We tested the technique in three helminths: Echinostoma paraensei, Cruzia tentaculata, and Hassalstrongylus epsilon. The results show that this technique could potentially be applied to study the morphology, ultrastructure, and taxonomy of helminths.