Study on the tolerance and adaptation of rats to Angiostrongylus cantonensis infection

Parasite Fauna and Coinfections in Urban Rats Naturally Infected by the Zoonotic Parasite Angiostrongylus cantonensis

When the zoonotic parasite of rodents that can cause human neuroangiostrongyliasis, i.e., Angiostrongylus cantonensis, is found in its natural definitive hosts, it is usually reported in isolation, as if the rat lungworm were the only component of its parasite community. In this study, we report the coinfections found in rats naturally infected by A. cantonensis in urban populations of Rattus norvegicus and Rattus rattus in Valencia, Spain. In addition to the rat lungworms, which were found in 14 of the 125 rats studied (a prevalence of 11.20%), 18 other parasite species (intestinal and tissular protists, microsporidia and helminths) were found, some of them with high burdens. Fourteen of these nineteen species found are potential zoonotic parasites, namely Blastocystis, Giardia duodenalis, Cryptosporidium spp., Enterocytozoon bieneusi, Encephalitozoon hellem, Toxoplasma gondii, Brachylaima spp., Hydatigera taeniaeformis s.l. larvae, Hymenolepis nana, Hymenolepis diminuta, Angiostrongylus cantonensis, Calodium hepaticum, Gongylonema neoplasticum and Moniliformis moniliformis. The total predominance of coinfected rats as well as their high parasite loads seem to indicate a trend towards parasite tolerance.

Core gut microbes Cloacibacterium and Aeromonas associated with different gastropod species could be persistently transmitted across multiple generations

BACKGROUND

Studies on the gut microbiota of animals have largely focused on vertebrates. The transmission modes of commensal intestinal bacteria in mammals have been well studied. However, in gastropods, the relationship between gut microbiota and hosts is still poorly understood. To gain a better understanding of the composition of gut microbes and their transmission routes in gastropods, a large-scale and long-term experiment on the dynamics and transmission modes of gut microbiota was conducted on freshwater snails.

RESULTS

We analyzed 244 microbial samples from the digestive tracts of freshwater gastropods and identified Proteobacteria and Bacteroidetes as dominant gut microbes. Aeromonas, Cloacibacterium, and Cetobacterium were identified as core microbes in the guts, accounting for over 50% of the total sequences. Furthermore, both core bacteria Aeromonas and Cloacibacterium, were shared among 7 gastropod species and played an important role in determining the gut microbial community types of both wild and cultured gastropods. Analysis of the gut microbiota at the population level, including wild gastropods and their offspring, indicated that a proportion of gut microbes could be consistently vertically transmitted inheritance, while the majority of the gut microbes resulted from horizontal transmission. Comparing cultured snails to their wild counterparts, we observed an increasing trend in the proportion of shared microbes and a decreasing trend in the number of unique microbes among wild gastropods and their offspring reared in a cultured environment. Core gut microbes, Aeromonas and Cloacibacterium, remained persistent and dispersed from wild snails to their offspring across multiple generations. Interestingly, under cultured environments, the gut microbiota in wild gastropods could only be maintained for up to 2 generations before converging with that of cultured snails. The difference observed in gut bacterial metabolism functions was associated with this transition. Our study also demonstrated that the gut microbial compositions in gastropods are influenced by developmental stages and revealed the presence of Aeromonas and Cloacibacterium throughout the life cycle in gastropods. Based on the dynamics of core gut microbes, it may be possible to predict the health status of gastropods during their adaptation to new environments. Additionally, gut microbial metabolic functions were found to be associated with the adaptive evolution of gastropods from wild to cultured environments.

CONCLUSIONS

Our findings provide novel insights into the dynamic processes of gut microbiota colonization in gastropod mollusks and unveil the modes of microbial transmission within their guts. Video Abstract.

Metagenomic Analysis Reveals Variations in Gut Microbiomes of the Schistosoma mansoni-Transmitting Snails Biomphalaria straminea and Biomphalaria glabrata

Biomphalaria snails play a crucial role in the transmission of the human blood fluke Schistosoma mansoni. The gut microbiota of intermediate hosts is known to influence their physiological functions, but little is known about its composition and role in Biomphalaria snails. To gain insights into the biological characteristics of these freshwater intermediate hosts, we conducted metagenomic sequencing on Biomphalaria straminea and B. glabrata to investigate variations in their gut microbiota. This study revealed that the dominant members of the gut microbiota in B. glabrata belong to the phyla Bacteroidetes and Proteobacteria, which were also found to be the top two most abundant gut bacteria in B. straminea. We identified Firmicutes, Acidovorax and Bosea as distinctive gut microbes in B. straminea, while Aeromonas, Cloacibacterium and Chryseobacterium were found to be dependent features of the B. glabrata gut microbiota. We observed significant differences in the community structures and bacterial functions of the gut microbiota between the two host species. Notably, we found a distinctive richness of antibiotic resistance genes (ARGs) associated with various classes of antibiotics, including bacitracin, chloramphenicol, tetracycline, sulfonamide, penicillin, cephalosporin_ii and cephalosporin_i, fluoroquinolone, aminoglycoside, beta-lactam, multidrug and trimethoprim, in the digestive tracts of the snails. Furthermore, this study revealed the potential correlations between snail gut microbiota and the infection rate of S. mansoni using Spearman correlation analysis. Through metagenomic analysis, our study provided new insights into the gut microbiota of Biomphalaria snails and how it is influenced by host species, thereby enhancing our understanding of variant patterns of gut microbial communities in intermediate hosts. Our findings may contribute to future studies on gastropod-microbe interactions and may provide valuable knowledge for developing snail control strategies to combat schistosomiasis in the future.

Comparative biology of parasitic nematodes in the genus Angiostrongylus and related genera

The rise to prominence of some Angiostrongylus species through associated emerging disease in humans and dogs has stimulated calls for a renewed focus on the biology of this genus and three related genera. Although significant research efforts have been made in recent years these have tended to focus on individual species and specific aspects such as diagnosis and treatment of disease or new records of occurrence and hosts. This comprehensive review takes a comparative approach, seeking commonalities and differences among species and asking such questions as: Which species belong to this and to closely related genera and how are they related? Why do only some species appear to be spreading geographically and what factors might underlie range expansion? Which animal species are involved in the life cycles as definitive, intermediate, paratenic and accidental hosts? How do parasite larvae find, infect and develop within these hosts? What are the consequences of infection for host health? How will climate change affect future spread and global health? Appreciating how species resemble and differ from each other shines a spotlight on knowledge gaps and provides provisional guidance on key species characteristics warranting detailed study. Similarities exist among species, including the basic life cycle and transmission processes, but important details such as host range, climatic requirements, migration patterns within hosts and disease mechanisms differ, with much more information available for A. cantonensis and A. vasorum than for other species. Nonetheless, comparison across Angiostrongylus reveals some common patterns. Historically narrow definitive host ranges are expanding with new knowledge, combining with very broad ranges of intermediate gastropod hosts and vertebrate and invertebrate paratenic and accidental hosts to provide the backdrop to complex interactions among climate, ecology and transmission that remain only partly understood, even for the species of dominant concern. Key outstanding questions concern larval dynamics and the potential for transmission outside trophic relations, relations between infection and disease severity in different hosts, and how global change is altering transmission beyond immediate impacts on development rate in gastropods. The concept of encounter and compatibility filters could help to explain differences in the relative importance of different gastropod species as intermediate hosts and determine the importance of host community composition and related environmental factors to transmission and range. Across the group, it remains unclear what, physiologically, immunologically or taxonomically, delimits definitive, accidental and paratenic hosts. Impacts of infection on definitive host fitness and consequences for population dynamics and transmission remain mostly unexplored across the genus. Continual updating and cross-referencing across species of Angiostrongylus and related genera is important to synthesise rapid advances in understanding of key traits and behaviours, especially in important Angiostrongylus species that are emerging causative agents of disease in humans and other animals.

Stat3/IL-6 signaling mediates sustained pneumonia induced by Agiostrongylus cantonensis

Angiostrongylus cantonensis (AC) is well-documented that parasitizes the host brain and causes eosinophilic meningitis. The migration route of AC in permissive hosts is well demonstrated, while in nonpermissive hosts, it remains to be fully defined. In the present study, we exploited live imaging technology, morphological and pathological configuration analysis, and molecular biological technologies to explore the migration route of AC and the accompanying tissue damage in nonpermissive and permissive hosts. Our data indicated that, in nonpermissive host mouse, AC larvae migrated from intestinal wall to liver at 2 hours post-infection (hpi), from liver to lung at 4 hpi and then from lung to brain at 8 hpi. AC larval migration caused fatal lung injury (pneumonia) during acute and early infection phases, along with significant activation of Stat3/IL-6 signaling. In addition, AC induce sustained interstitial pneumonia in mouse and rat and pulmonary fibrosis only in rat during late infection phase. Moreover, during the early and late infection phases, Th2 cytokine expression and Stat3 and IL-6 signaling were persistently enhanced and myeloid macrophage cells were notably enriched in host lung, and administration of Stat3 and IL-6 inhibitors (C188-9 and LMT-28) attenuated AC infection-induced acute pneumonia in mice. Overall, we are the first to provide direct and systemic laboratory evidence of AC migration route in a nonpermissive host and report that infection with a high dose of AC larvae could result in acute and fatal pneumonia through Stat3/IL-6 signaling in mice. These findings may present a feasible to rational strategy to minimize the pathogenesis induced by AC.

Angiostrongylus cantonensis is a well-known nematode parasitizing the host brain and is the leading cause of eosinophilic meningitis worldwide. Our study reports the migration route of Angiostrongylus cantonensis larvae in non-permissive host mouse and discovers that the larvae could induce fatal pneumonia in mouse lung during acute and early infection phase characterized by activation of Stat3/IL-6 signaling. Moreover, administration of inhibitors targeting Stat3/IL-6 signaling could significantly attenuate the AC-induced pneumonia of non-permissive host mouse, providing an effective candidate target for intervention of this severe parasitic pneumonia. These findings expand our understanding of Angiostrongyliasis cantonensis and indicate that more attention to AC-induced pneumonia is required when treatment for Angiostrongyliasis cantonensis in the future.

In vivo efficacy of pyrantel pamoate as a post-exposure prophylactic for rat lungworm (Angiostrongylus cantonensis)

Rat lungworm (Angiostrongylus cantonensis) is a neurotropic nematode, and the leading cause of eosinophilic meningitis worldwide. The parasite is usually contracted through ingestion of infected gastropods, often hidden in raw or partially cooked produce. Pharmaceutical grade pyrantel pamoate was evaluated as a post-exposure prophylactic against A. cantonensis. Pyrantel pamoate is readily available over-the-counter in most pharmacies in the USA and possesses anthelmintic activity exclusive to the gastrointestinal tract (GIT). Administering pyrantel pamoate immediately after exposure should theoretically paralyze the larvae in the GIT, causing the larvae to be expelled via peristalsis without entering the systemic circulation. In this study, pyrantel pamoate (11 mg/kg) was orally administered to experimentally infected rats at 0, 2-, 4-, 6-, or 8-h post-infection. The rats were euthanized six weeks post-infection, and worm burden was evaluated from the heart-lung complex. This is the first in vivo study to evaluate its efficacy against A. cantonensis. This study demonstrates that pyrantel pamoate can significantly reduce worm burden by 53–72% (P = 0.004), and thus likely reduce the severity of infection that is known to be associated with worm burden. This paralyzing effect of pyrantel pamoate on the parasite may also be beneficial for delaying the establishment of infection until a more suitable anthelmintic such as albendazole is made available to the patient.

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Pyrantel pamoate (PP) shows significant in vivo efficacy against A. cantonensis.

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Efficacy of PP was evaluated for the first time in an experimental animal model.

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Administering PP between 4 and 8 h post-exposure significantly reduces worm burden.

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PP is a new post-exposure prophylactic for rat lungworm disease.

Larvicidal Efficacy of Ozone and Ultrasound on Angiostrongylus cantonensis (Rat Lungworm) Third-Stage Larvae

The parasitic nematode Angiostrongylus cantonensis (rat lungworm) is the leading cause of human eosinophilic meningitis worldwide. Most human infections occur through the accidental consumption of A. cantonensis hidden within produce as infectious third-stage larvae (L3), yet little research has been published addressing possible methods to mitigate this means of transmission. Here, we describe our tests of ozone gas—an oxidizing agent—and ultrasound, both used for disinfection of food and municipal water supplies and in industrial cleaning. We found that exposure to ozone, produced using two different commercially available ozone generators over varying durations of time and concentrations, was capable of achieving 100% larval mortality. In addition, we evaluated the impact of different sound frequencies on A. cantonensis L3 survival using two different commercially available ultrasonic cleaners, and found that 60 s of 40 kHz produced 46% mortality within 2 h. The combined use of ultrasound and ozone gas simultaneously resulted in a minimum of 89% normalized mean percent mortality within 2 h of treatment. Our study suggests that both ozone and ultrasound show high larvicidal efficacy, both independently and together, and thus show promise as methods for reducing the risk of rat lungworm infection via accidental consumption.

IL-17A Mediates Demyelination by Activating A1 Astrocytes via SOCS3 During Angiostrongylus cantonensis Infection

Background

Demyelinating disease of the central nervous system is one of the most common neurological diseases and effective treatment is still under in-depth research. Our previous study showed that Angiostrongylus cantonensis infection can induce demyelination injury in mouse brains and IL-17A expression was shown to be significantly increased during this process. Moreover, we found that IL-17A inhibition attenuated the demyelination caused by A. cantonensis infection. However, the underlying mechanisms have not yet been fully elucidated.

Methods

IL-17A neutralizing antibodies were injected into A. cantonensis infected mice to decrease IL-17A levels. The activation of glial cells in the brain and the expression of cell markers were detected by a variety of methods, including real-time quantitative PCR, western blotting, and immunofluorescence staining. The relationship between IL-17A and astrocyte activation was further identified by in vitro experiments. The role of SOCS3 in the IL-17A stimulating process was determined using RNA-seq data collection of infected mice and the siRNA interference method.

Results

Demyelination of the corpus callosum was relieved after administration of IL-17A neutralizing antibody and this was accompanied by decreased activation of A1 type astrocytes around this region. The expression of SOCS3 was attenuated and activation of astrocytes by IL-17A was mediated by the IL-17RA/STAT3/SOCS3 pathway. IL-17A not only directly damaged oligodendrocytes but also indirectly damaged oligodendrocytes through A1 astrocyte mediation. Specific siRNA inhibition of IL-17A-inducible SOCS3 in astrocytes alleviated their damaging effects on oligodendrocytes.

Conclusion

IL-17A plays an important role in demyelination induced by A. cantonensis infection via the IL-17RA/STAT3/SOCS3 pathway in A1-type astrocytes, indicating that specific blockage of IL-17A and SOCS3 activity could be a therapeutic strategy for neuroinflammatory demyelinating diseases associated with astrocyte activation.

Clinical Efficacy and Safety of Albendazole and Other Benzimidazole Anthelmintics for Rat Lungworm Disease (Neuroangiostrongyliasis): A Systematic Analysis of Clinical Reports and Animal Studies

The safety and efficacy of benzimidazole anthelmintics for the treatment of rat lungworm disease (neuroangiostrongyliasis) have been questioned regardless of numerous experimental animal studies and clinical reports. In this review, 40 of these experimental animal studies and 104 clinical reports are compiled with a focus on albendazole. Among the 144 articles involving an estimated 1034 patients and 2561 animals, 4.1% were inconclusive or vague regarding the use of benzimidazoles. Of the remaining 138 articles, 90.5% found benzimidazoles to be safe and effective (885 patients, 2530 animals), 4.3% as safe but ineffective (73 patients, 3 animals), and 5.0% caused adverse reactions (7 patients, 28 animals). Among those clinical reports that described a confirmed diagnosis of neuroangiostrongyliasis in which albendazole monotherapy was used, 100% reported high efficacy (743 patients, 479 animals). In those where albendazole-corticosteroid co-therapy was used, 97.87% reported it to be effective (323 patients, 130 animals).

Interleukin 17A Derived from γδ T Cell Induces Demyelination of the Brain in Angiostrongylus cantonensis Infection

Angiostrongylus cantonensis infection is a typical cause of eosinophilic encephalitis (EM), which has been reported to induce serious damage in the central nervous system. Both parasite and host factors contribute to the onset of EM, but the related immune-inflammation pathogenesis remains poorly characterised. An A. cantonensis infection model was generated through the infection of mice by gavage. Transmission electron microscopy and immunohistochemistry were used to assess the pathologic changes in the brain. The mRNA expression of inflammatory factors was tested using qRT-PCR. A combination of flow cytometry and western blotting was used to evaluate the alteration of leukocytes and related cytokines. A critical role of IL-17 was found by injecting IL-17A monoclonal antibody into naïve and A. cantonensis-infected mice. A. cantonensis larvae altered the immune homeostasis in the brain, leading to the destruction of myelin sheaths and activation of microglia and macrophage. During this process, IL-17A accumulation was observed, and IL-17RA was expressed in oligodendrocytes and microglia during the infection. Notably, γδ T cell was the major origin of IL-17A production induced by the parasite. After an IL-17A-neutralising antibody was applied, alterations in myelination and the state of the microglia/macrophage were discovered; the neurobehavioural scores of the mice also improved. Our study reveals one unrecognised impact of the γδ T cells in parasitic encephalopathy and emphasises that blocking IL-17A signalling can attenuate microglia and macrophage activation, thus reducing CNS demyelination and ameliorating the neurobehavioural deficit in A. cantonensis-infected mice.

TNF-α Triggers RIP1/FADD/Caspase-8-Mediated Apoptosis of Astrocytes and RIP3/MLKL-Mediated Necroptosis of Neurons Induced by Angiostrongylus cantonensis Infection

Angiostrongylus cantonensis (AC) can cause severe eosinophilic meningitis or encephalitis in non-permissive hosts accompanied by apoptosis and necroptosis of brain cells. However, the explicit underlying molecular basis of apoptosis and necroptosis upon AC infection has not yet been elucidated. To determine the specific pathways of apoptosis and necroptosis upon AC infection, gene set enrichment analysis (GSEA) and protein-protein interaction (PPI) analysis for gene expression microarray (accession number: GSE159486) of mouse brain infected by AC revealed that TNF-α likely played a central role in the apoptosis and necroptosis in the context of AC infection, which was further confirmed via an in vivo rescue assay after treating with TNF-α inhibitor. The signalling axes involved in apoptosis and necroptosis were investigated via immunoprecipitation and immunoblotting. Immunofluorescence was used to identify the specific cells that underwent apoptosis or necroptosis. The results showed that TNF-α induced apoptosis of astrocytes through the RIP1/FADD/Caspase-8 axis and induced necroptosis of neurons by the RIP3/MLKL signalling pathway. In addition, in vitro assay revealed that TNF-α secretion by microglia increased upon LSA stimulation and caused necroptosis of neurons. The present study provided the first evidence that TNF-α was secreted by microglia stimulated by AC infection, which caused cell death via parallel pathways of astrocyte apoptosis (mediated by the RIP1/FADD/caspase-8 axis) and neuron necroptosis (driven by the RIP3/MLKL complex). Our research comprehensively elucidated the mechanism of cell death after AC infection and provided new insight into targeting TNF-α signalling as a therapeutic strategy for CNS injury.

In vitro efficacy of anthelmintics on Angiostrongylus cantonensis L3 larvae

Angiostrongylus cantonensis is the leading cause of eosinophilic meningitis worldwide, with life-threatening complications if not managed correctly. Previous in vitro studies have utilized change in motility patterns of adult female worms to assess the efficacy of anthelmintics qualitatively. However, it is the third stage larvae (L3) that are infectious to humans. With differential staining using propidium iodide penetration as the indicator of death, we can distinguish between dead and live larvae. This assay has enabled us to quantify the in vitro efficacy of nine clinically established anthelmintics on A. cantonensis L3. All drugs were tested at a 1 mm concentration. Piperazine and niclosamide were ineffective in inducing larval death; however, albendazole sulfoxide, pyrantel pamoate, diethylcarbamazine, levamisole and praziquantel were effective as compared to unexposed controls (P < 0.05). Ivermectin and moxidectin did not induce significant levels of mortality, but they considerably reduced larval motility almost immediately. This study indicates the need for further in vivo studies to determine the optimal dose and time frame for post-infection treatment with anthelmintics that demonstrated efficacy.

Variation in Angiostrongylus cantonensis infection in definitive and intermediate hosts in Hawaii, a global hotspot of rat lungworm disease

Angiostrongylus cantonensis (rat lungworm) is a tropical and subtropical parasitic nematode, with infections in humans causing angiostrongyliasis (rat lungworm disease), characterized by eosinophilic meningitis. Hawaii has been identified as a global hotspot of infection, with recent reports of high infection rates in humans, as well as rat definitive and snail intermediate hosts. This study investigated variation in A. cantonensis infection, both prevalence and intensity, in wild populations of two species of rats (Rattus exulans and R. rattus) and one species of snail (Parmarion martensi). An overall infection prevalence of 86.2% was observed in P. martensi and 63.8% in rats, with R. exulans (77.4%) greater than R. rattus (47.6%). We found infections to vary with environmental and host-related factors. Body mass was a strong predictor of infection in all three species, with different patterns seen between sexes and species of rats. Infection prevalence and intensity for R. exulans were high in May 2018 and again in February 2019, but generally lower and more variable during the intervening months. Information on sources of variability of infection in wild host populations will be a crucial component in predicting the effectiveness of future disease surveillance or targeted management strategies.

Necroptosis and Caspase-2-Mediated Apoptosis of Astrocytes and Neurons, but Not Microglia, of Rat Hippocampus and Parenchyma Caused by Angiostrongylus cantonensis Infection

Infection with the roundworm Angiostrongylus cantonensis is the main cause of eosinophilic meningitis worldwide. The underlying molecular basis of the various pathological outcomes in permissive and non-permissive hosts infected with A. cantonensis remains poorly defined. In the present study, the histology of neurological disorders in the central nervous system (CNS) of infected rats was assessed by using hematoxylin and eosin staining. Quantitative reverse transcription polymerase chain reaction (RT-qPCR), western blot and immunofluorescence (IF) were used in evolutions of the transcription and translation levels of the apoptosis-, necroptosis-, autophagy-, and pyroptosis-related genes. The distribution of apoptotic and necroptotic cells in the rat hippocampus and parenchyma was further detected using flow cytometry, and the features of the ultrastructure of the cells were examined by transmission electron microscopy (TEM). The inflammatory response upon CNS infection with A. cantonensis evolved, as characterized by the accumulation of a small number of inflammatory cells under the thickened meninges, which peaked at 21 days post-infection (dpi) and returned to normal by 35 dpi. The transcription levels and translation of caspase-2, caspase-8, RIP1 and RIP3 increased significantly at 21 and 28 dpi but decreased sharply at 35 dpi compared to those in the normal control group. However, the changes in the expression of caspase-1, caspase-3, caspase-11, Beclin-1 and LC3B were not obvious, suggesting that apoptosis and necroptosis but not autophagy or pyroptosis occurred in the brains of infected animals at 21 and 28 dpi. The results of RT-qPCR, western blot analysis, IF, flow cytometry and TEM further illustrated that necroptosis and caspase-2-mediated apoptosis occurred in astrocytes and neurons but not in microglia in the parenchyma and hippocampus of infected animals. This study provides the first evidence that neuronal and astrocytic necroptosis and caspase-2-mediated apoptosis are induced by A. cantonensis infection in the parenchymal and hippocampal regions of rats at 21 and 28 dpi but these processes are negligible at 35 dpi. These findings enhance our understanding of the pathogenesis of A. cantonensis infection and provide new insights into therapeutic approaches targeting the occurrence of cell death in astrocytes and neurons in infected patients.

Apoptosis and necroptosis of mouse hippocampal and parenchymal astrocytes, microglia and neurons caused by Angiostrongylus cantonensis infection

BACKGROUND

Angiostrongylus cantonensis has been the only parasite among Angiostrongylidae to cause human central nervous system infection characterized by eosinophilic meningitis or meningoencephalitis. The mechanism of the extensive neurological impairments of hosts caused by A. cantonensis larvae remains unclear. The aim of the present study was to investigate apoptosis, necroptosis and autophagy in the brains of mice infected with A. cantonensis, which will be valuable for better understanding the pathogenesis of angiostrongyliasis cantonensis.

METHODS

Functional and histological neurological impairments of brain tissues from mice infected with A. cantonensis were measured by the Morris water maze test and haematoxylin and eosin (H&E) staining, respectively. The transcriptional and translational levels of apoptosis-, necroptosis- and autophagy-related genes were quantified by quantitative real-time polymerase chain reaction (RT-PCR), and assessed by western blot and immunohistochemistry (IHC) analysis. Apoptotic and necroptotic cells and their distributions in infected brain tissues were analysed by flow cytometry and transmission electron microscopy (TEM).

RESULTS

Inflammatory response in the central nervous system deteriorated as A. cantonensis infection evolved, as characterized by abundant inflammatory cell infiltration underneath the meninges, which peaked at 21 days post-infection (dpi). The learning and memory capacities of the mice were significantly decreased at 14 dpi, indicating prominent impairment of their cognitive functions. Compared with those of the control group, the mRNA levels of caspase-3, -4, -6, and RIP3 and the protein levels of caspase-4, cleaved caspase-3, cleaved caspase-6, RIP3, and pRIP3 were obviously elevated. However, no changes in the mRNA or protein levels of FADD, Beclin-1 or LC3B were evident, indicating that apoptosis and necroptosis, but not autophagy, occurred in the brain tissues of mice infected with A. cantonensis. The quantitative RT-PCR, western blot, IHC, flow cytometry and TEM results further revealed the apoptotic and necroptotic microglia, astrocytes and neurons in the parenchymal and hippocampal regions of infected mice.

CONCLUSIONS

To our knowledge, we showed for the first time that A. cantonensis infection causes the apoptosis and necroptosis of microglia and astrocytes in the parenchymal and hippocampal regions of host brain tissues, further demonstrating the pathogenesis of A. cantonensis infection and providing potential therapeutic targets for the management of angiostrongyliasis.

Inhibiting Interleukin 17 Can Ameliorate the Demyelination Caused by A. cantonensis via iNOS Inhibition

Angiostrongylus cantonensis (A. cantonensis) is an important food-borne parasitic disease. Previous study showed that A. cantonensis infection can cause demyelination in the central nerve system, but the mechanism of action has not been understood. To explore the mechanism and to look for effective therapeutic methods, interleukin 17A (IL-17A) and iNOS expressions were detected during A. cantonensis infection. In addition, IL-17A-neutralizing antibody was applied to treat A. cantonensis-infected mice. In our results, we found that IL-17A and iNOS RNA expressions increased gradually in the process of A. cantonensis infection. When infected mice were treated with IL-17A-neutralizing antibody, the pathologic changes of demyelination alleviated obviously, followed with the elevation of myelin basic protein (MBP) in the brain. In addition, the iNOS expression of the brain in infected animals also showed a decrease in astrocytes. Our study provided evidence that IL-17A may take part in the demyelination caused by A. cantonensis and inhibiting IL-17A expression can ameliorate the pathologic changes of demyelination. Moreover, the decreasing of iNOS expression may be the key reason for the effect of IL-17A inhibition on demyelination caused by A. cantonensis.