Microarray gene expression analysis reveals major differences between Toxocara canis and Toxocara cati neurotoxocarosis and involvement of T. canis in lipid biosynthetic processes

Infectious origin of Alzheimer’s disease: Amyloid beta as a component of brain antimicrobial immunity

The amyloid cascade hypothesis, focusing on pathological proteins aggregation, has so far failed to uncover the root cause of Alzheimer’s disease (AD), or to provide an effective therapy. This traditional paradigm essentially explains a mechanism involved in the development of sporadic AD rather than its cause. The failure of an overwhelming majority of clinical studies (99.6%) demonstrates that a breakthrough in therapy would be difficult if not impossible without understanding the etiology of AD. It becomes more and more apparent that the AD pathology might originate from brain infection. In this review, we discuss a potential role of bacteria, viruses, fungi, and eukaryotic parasites as triggers of AD pathology. We show evidence from the current literature that amyloid beta, traditionally viewed as pathological, actually acts as an antimicrobial peptide, protecting the brain against pathogens. However, in case of a prolonged or excessive activation of a senescent immune system, amyloid beta accumulation and aggregation becomes damaging and supports runaway neurodegenerative processes in AD. This is paralleled by the recent study by Alam and colleagues (2022) who showed that alpha-synuclein, the protein accumulating in synucleinopathies, also plays a critical physiological role in immune reactions and inflammation, showing an unforeseen link between the 2 unrelated classes of neurodegenerative disorders. The multiplication of the amyloid precursor protein gene, recently described by Lee and collegues (2018), and possible reactivation of human endogenous retroviruses by pathogens fits well into the same picture. We discuss these new findings from the viewpoint of the infection hypothesis of AD and offer suggestions for future research.

More than a century after its discovery, Alzheimer’s disease (AD) remains incurable and mysterious. The dominant hypothesis of amyloid cascade has succeeded in explaining the key pathological mechanism, but not its trigger. Amyloid beta has been traditionally considered a pathological peptide, and its physiological functions remain poorly known. These knowledge gaps have contributed to repeated failures of clinical studies. The emerging infectious hypothesis of AD considers central nervous system (CNS) infection the primary trigger of sporadic AD. A closely connected hypothesis claims that amyloid beta is an antimicrobial peptide. In this review, we discuss the available evidence for the involvement of infections in AD, coming from epidemiological studies, post mortem analyses of brain tissue, and experiments in vitro and in vivo. We argue there is no unique “Alzheimer’s germ,” instead, AD is a general reaction of the CNS to chronic infections, in the milieu of an aged immune system. The pathology may become self-sustained even without continuous presence of microbes in the brain. Importantly, the infectious hypothesis leads to testable predictions. Targeting amyloid beta should be ineffective, unless the triggering pathogen and inflammatory response are addressed as well. Meticulous control of selected infections might be the best near-term strategy for AD prevention.

Lung Lipidomic Alterations in Beagle Dogs Infected with Toxocara canis

Toxocariasis, mainly caused by Toxocara canis, and to a lesser extent, Toxocara cati, is a neglected parasitic zoonosis. The mechanisms that underlie the changes in lipid metabolism of T. canis infection in Beagle dogs' lungs remain unclear. Lipidomics is a rapidly emerging approach that enables the global profiling of lipid composition by mass spectrometry. In this study, we performed a non-targeted lipidomic analysis of the lungs of Beagle dogs infected with the roundworm T. canis using liquid chromatography-tandem mass spectrometry (LC-MS/MS). A total of 1197 lipid species were identified, of which 63, 88, and 157 lipid species were significantly altered at 24 h post-infection (hpi), 96 hpi, and 36 days post-infection (dpi), respectively. This global lipidomic profiling identified infection-specific lipid signatures for lung toxocariasis, and represented a comprehensive comparison between the lipid composition of dogs' lungs in the presence and absence of T. canis infection. The potential roles of the identified lipid species in the pathogenesis of T. canis are discussed, which has important implications for better understanding the interaction mechanism between T. canis and the host lung.

Mechanisms of the host immune response and helminth-induced pathology during Trichobilharzia regenti (Schistosomatidae) neuroinvasion in mice

Helminth neuroinfections represent serious medical conditions, but the diversity of the host-parasite interplay within the nervous tissue often remains poorly understood, partially due to the lack of laboratory models. Here, we investigated the neuroinvasion of the mouse spinal cord by Trichobilharzia regenti (Schistosomatidae). Active migration of T. regenti schistosomula through the mouse spinal cord induced motor deficits in hindlimbs but did not affect the general locomotion or working memory. Histological examination of the infected spinal cord revealed eosinophilic meningomyelitis with eosinophil-rich infiltrates entrapping the schistosomula. Flow cytometry and transcriptomic analysis of the spinal cord confirmed massive activation of the host immune response. Of note, we recorded striking upregulation of the major histocompatibility complex II pathway and M2-associated markers, such as arginase or chitinase-like 3. Arginase also dominated the proteins found in the microdissected tissue from the close vicinity of the migrating schistosomula, which unselectively fed on the host nervous tissue. Next, we evaluated the pathological sequelae of T. regenti neuroinvasion. While no demyelination or blood-brain barrier alterations were noticed, our transcriptomic data revealed a remarkable disruption of neurophysiological functions not yet recorded in helminth neuroinfections. We also detected DNA fragmentation at the host-schistosomulum interface, but schistosomula antigens did not affect the viability of neurons and glial cells in vitro. Collectively, altered locomotion, significant disruption of neurophysiological functions, and strong M2 polarization were the most prominent features of T. regenti neuroinvasion, making it a promising candidate for further neuroinfection research. Indeed, understanding the diversity of pathogen-related neuroinflammatory processes is a prerequisite for developing better protective measures, treatment strategies, and diagnostic tools.

Toxocara canis- and Toxocara cati-Induced Neurotoxocarosis Is Associated with Comprehensive Brain Transcriptomic Alterations

Toxocara canis and Toxocara cati are globally occurring zoonotic roundworms of dogs and cats. Migration and persistence of Toxocara larvae in the central nervous system of paratenic hosts including humans may cause clinical signs of neurotoxocarosis (NT). As pathomechanisms of NT and host responses against Toxocara larvae are mostly unknown, whole-genome microarray transcription analysis was performed in cerebra and cerebella of experimentally infected C57Bl/6J mice as paratenic host model at days 14, 28, 70, 98, and 120 post-infection. Neuroinvasion of T. cati evoked 220 cerebral and 215 cerebellar differentially transcribed genes (DTGs), but no particular PANTHER (Protein ANalysis THrough Evolutionary Relationships) pathway was affected. In T. canis-infected mice, 1039 cerebral and 2073 cerebellar DTGs were identified. Statistically significant dysregulations occurred in various pathways, including cholesterol biosynthesis, apoptosis signaling, and the Slit/Robo mediated axon guidance as well as different pathways associated with the immune and defense response. Observed dysregulations of the cholesterol biosynthesis, as well as the Alzheimer disease-amyloid secretase pathway in conjunction with previous histopathological neurodegenerative findings, may promote the discussion of T. canis as a causative agent for dementia and/or Alzheimer’s disease. Furthermore, results contribute to a deeper understanding of the largely unknown pathogenesis and host-parasite interactions during NT, and may provide the basis for prospective investigations evaluating pathogenic mechanisms or designing novel diagnostic and therapeutic approaches.

Toxocara canis Infection Alters lncRNA and mRNA Expression Profiles of Dog Bone Marrow

Bone marrow is the main hematopoietic organ that produces red blood cells, granulocytes, monocyte/macrophages, megakaryocytes, lymphocytes, and myeloid dendritic cells. Many of these cells play roles in the pathogenesis of Toxocara canis infection, and understanding how infection alters the dynamics of transcription regulation in bone marrow is therefore critical for deciphering the global changes in the dog transcriptional signatures during T. canis infection. In this study, long non-coding RNA (lncRNA) and messenger RNA (mRNA) expression profiles in the bone marrow of Beagle dogs infected with T. canis were determined at 12 h post-infection (hpi), 24 hpi, 96 hpi, and 36 days post-infection (dpi). RNA-sequencing and bioinformatics analysis identified 1,098, 984, 1,120, and 1,305 differentially expressed lncRNAs (DElncRNAs), and 196, 253, 223, and 328 differentially expressed mRNAs (DEmRNAs) at 12 h, 24 h, 96 h, and 36 days after infection, respectively. We also identified 29, 36, 38, and 68 DEmRNAs potentially cis-regulated by 44, 44, 51, and 80 DElncRNAs at 12 hpi, 24 hpi, 96 hpi, and 36 dpi, respectively. To validate the sequencing findings, qRT-PCR was performed on 10 randomly selected transcripts. Many altered genes were involved in the differentiation of bone marrow cells. GO of DElncRNAs and GO and KEGG pathway analyses of DEmRNAs revealed alterations in several signaling pathways, including pathways involved in energy metabolism, amino acid biosynthesis and metabolism, Wnt signaling pathway, Huntington's disease, HIF-1 signaling pathway, cGMP–PKG signaling pathway, dilated cardiomyopathy, and adrenergic signaling in cardiomyocytes. These findings revealed that bone marrow of T. canis-infected dogs exhibits distinct lncRNA and mRNA expression patterns compared to healthy control dogs. Our data provide novel insights into T. canis interaction with the definitive host and shed light on the significance of the non-coding portion of the dog genome in the pathogenesis of toxocariasis.

Toxocara infection/exposure and the risk of schizophrenia: a systematic review and meta-analysis

Toxocariasis is an important neglected disease that could have a role in the development of some neurological disorders, such as schizophrenia (SCZ). We performed the first systematic review and meta-analysis on observational studies to evaluate the possible association between Toxocara infection/exposure and SCZ. Systematic searching (PubMed, Scopus, Web of Science and Google Scholar) was performed, up to 15 August 2020, to identify the relevant studies. We used a random effects meta-analysis model to generate the pooled OR and 95% CIs. The research process resulted in the identification of six studies related to the subject of interest entailing 411 SCZ patients and 2047 controls. Our results demonstrated that the SCZ patients (15%; 95% CI 6.8 to 29.9%) had higher pooled seroprevalence of Toxocara infection/exposure than the control group (3.3%; 95% CI 1.1 to 9.4%), showing a significant association (pooled OR, 4.06; 95% CI 1.14 to 14.43). Our findings suggested that Toxocara infection/exposure might have an important but neglected contribution to SCZ development. However, further well-designed and large-scale observational studies are needed to illuminate this association. Because many other environmental and genetic factors may be strong confounders, more mechanistic/experimental studies in animal models are also necessary to further define the mechanism of this association.

Global profiling of lncRNAs-miRNAs-mRNAs reveals differential expression of coding genes and non-coding RNAs in the lung of beagle dogs at different stages of Toxocara canis infection

The roundworm Toxocara canis causes toxocariasis in dogs and larval migrans in humans. Better understanding of the lung response to T. canis infection could explain why T. canis must migrate to and undergoes part of its development inside the lung of the definitive host. In this study, we profiled the expression patterns of long non-coding RNAs (lncRNAs), microRNAs (miRNAs), and mRNAs in the lungs of Beagle dogs infected by T. canis, using high throughput RNA sequencing. At 24 h p.i., 1,012 lncRNAs, 393 mRNAs and 10 miRNAs were differentially expressed (DE). We also identified 883 DElncRNAs, 264 DEmRNAs and 20 DEmiRNAs at 96 h p.i., and 996 DElncRNAs, 342 DEmRNAs and eight DEmiRNAs at 36 days p.i., between infected and control dogs. Significant changes in the levels of expression of transcripts related to immune response and inflammation were associated with the antiparasitic response of the lung to T. canis. The remarkable increase in the expression of scgb1a1 at all time points after infection suggests the need for consistent moderation of the excessive inflammatory response. Also, upregulation of foxj1 at 24 h p.i., and downregulation of IL-1β and IL-21 at 96 h p.i., suggest an attenuation of the humoral immunity of infected dogs. These results indicate that T. canis pathogenesis in the lung is mediated through contributions from both pro-inflammatory and anti-inflammatory mechanisms. Competing endogenous RNA (ceRNA) network analysis revealed significant interactions between DElncRNAs, DEmiRNAs and DEmRNAs, and improved our understanding of the ceRNA regulatory mechanisms in the context of T. canis infection. These data provide comprehensive understanding of the regulatory networks that govern the lung response to T. canis infection and reveal new mechanistic insights into the interaction between the host and parasite during the course of T. canis infection in the canine.

Toxocara "omics" and the promises it holds for medicine and veterinary medicine

Toxocariasis is one of the most neglected worldwide zoonoses that is caused by larval nematode parasites of the genus Toxocara, Toxocara canis, and to a lesser extent, Toxocara cati, whose migration mechanism is still largely unknown. Fortunately, some advanced tools have been employed, such as genomics, transcriptomics, and proteomics, to better understand the molecular biology and regulatory mechanisms of Toxocara. Using genomics and transcriptomics, we can identify a large number of genes that participate in the development of Toxocara and the interaction of parasites and their hosts and can predict the functions of unknown genes by comparing them with other relevant species. Using proteomics, we can identify somatic proteins and excretory and secretory (ES) proteins that perform specific biological functions in tissue degradation, pathogen invasion, immune evasion or modulation. These "omics" techniques also can contribute enormously to the development of new drugs, vaccines and diagnostic tools for toxocariasis. In a word, by utilizing "omics", we can better understand the Toxocara and toxocariasis. In this review, we summarized the representative achievements in Toxocara and the interaction between Toxocara spp. and their hosts based on expressed sequence tags (ESTs), microarray gene expression, next-generation sequencing (NGS) technologies and liquid chromatography-tandem mass spectrometry (LC-MS/MS), hoping to better understand the molecular biology of Toxocara, and contribute to new progress in the application areas of new drugs, vaccines and diagnostic tool for toxocariasis in the future.

Toxocara-induced neural larva migrans (neurotoxocarosis) in rodent model hosts

Neural larva migrans (NLM), or neurotoxocarosis, induced by Toxocara canis or Toxocara cati results from migrating and persisting larvae in the central nervous system of paratenic hosts, including humans. As the diagnosis of NLM in humans is not straightforward, most knowledge on the disease is derived from only a few published clinical cases. To improve our understanding of human NLM, studies on the pathogenesis and clinical symptoms in laboratory animal model systems are indispensable, and rodents have been accepted as the most appropriate model organisms for NLM. As research has mostly focused on neuroinvasive T. canis-larvae, information regarding the pathogenesis of T. cati-induced NLM remains scarce. This review summarises the current state of knowledge on neuroinvasion by both T. canis and T. cati in different rodent model hosts, the resulting behavioural changes, and histopathological alterations during the course of NLM as well as the potential molecular pathogenic mechanisms.

Multiplex profiling of inflammation-related bioactive lipid mediators in Toxocara canis- and Toxocara cati-induced neurotoxocarosis

Background

Somatic migration of Toxocara canis- and T. cati-larvae in humans may cause neurotoxocarosis (NT) when larvae accumulate and persist in the central nervous system (CNS). Host- or parasite-induced immunoregulatory processes contribute to the pathogenesis; however, detailed data on involvement of bioactive lipid mediators, e.g. oxylipins or eico-/docosanoids, which are involved in the complex molecular signalling network during infection and inflammation, are lacking.

Methodology/Principal findings

To elucidate if T. canis- and T. cati-induced NT affects the homeostasis of oxylipins during the course of infection, a comprehensive lipidomic profiling in brains (cerebra and cerebella) of experimentally infected C57BL/6J mice was conducted at six different time points post infection (pi) by liquid-chromatography coupled to electrospray tandem mass spectrometry (LC-ESI-MS/MS). Only minor changes were detected regarding pro-inflammatory prostaglandins (cyclooxygenase pathway). In contrast, a significant increase of metabolites resulting from lipoxygenase pathways was observed for both infection groups and brain regions, implicating a predominantly anti-inflammatory driven immune response. This observation was supported by a significantly increased 13-hydroxyoctadecadienoic acid (HODE)/9-HODE ratio during the subacute phase of infection, indicating an anti-inflammatory response to neuroinfection. Except for the specialised pro-resolving mediator (SPM) neuroprotectin D1 (NPD1), which was detected in mice infected with both pathogens during the subacute phase of infection, no other SPMs were detected.

Conclusions/Significance

The obtained results demonstrate the influence of Toxocara spp. on oxylipins as part of the immune response of the paratenic hosts. Furthermore, this study shows differences in the alteration of the oxylipin composition between T. canis- and T. cati-brain infection. Results contribute to a further understanding of the largely unknown pathogenesis and mechanisms of host-parasite interactions during NT.

Neurotoxocarosis (NT) is induced by larvae of the zoonotic roundworms Toxocara canis and T. cati migrating and persisting in the central nervous system of paratenic hosts, and may be accompanied by severe neurological symptoms. Toxocara spp. are known to modulate the hosts’ immune response, but data concerning involvement of signalling molecules are lacking. An important class of mediators participating in the complex molecular signalling network during infection and inflammation are bioactive regulatory lipids, derived from arachidonic acid and other polyunsaturated fatty acids. For a better understanding of inflammatory processes in the brain during an infection with Toxocara spp., a comprehensive analysis of regulatory lipids was conducted. The infection was predominantly characterised by only minor changes in the pattern of pro-inflammatory oxylipins, while anti-inflammatory metabolites, derived from lipoxygenase pathways, were significantly elevated in the subacute phase as well as in the beginning of the chronic phase of infection. This trend was also reflected in the 13-HODE/9-HODE ratio, a biomarker for the immunological status of an active infection. Obtained data provide a valuable insight in the host’s immune reaction as response against neuroinvasive Toxocara spp.-larvae, contributing to the characterisation of the mostly unknown pathogenesis of NT.

Histopathological characterization of Toxocara canis- and T. cati-induced neurotoxocarosis in the mouse model

Infective larvae of Toxocara canis and T. cati, the common roundworms of dogs and cats, may invade the central nervous system of paratenic hosts, including humans, causing neurotoxocarosis (NT). Previous studies on NT in the model organism "mouse" have indicated distinct differences between T. canis and T. cati regarding larval migration patterns as well as the severity of clinical symptoms and behavioural alterations. The objective of the present study was to provide an extensive characterization of the underlying histopathological alterations, comparing T. canis- and T. cati-induced changes in different brain areas over the course of murine infection. Four histological sections of five brains each of T. canis- and T. cati-infected as well as uninfected C57Bl/6 mice were investigated 7, 14, 28, 42, 70 and 98 days post infection (dpi), while brains of T. cati-infected and control mice were also available 120 and 150 dpi. In addition to haematoxylin-eosin and luxol fast blue-cresyl violet staining, immunohistochemistry was employed to study microglia/macrophage cell morphology and to detect accumulation of β-amyloid precursor protein (β-APP) as an indicator of axonal damage. Haemorrhages, eosinophilic vasculitis and activated microglia/macrophages were detected in both infection groups starting 7 dpi, followed by eosinophilic meningitis in cerebra as from 14 dpi. Overall, little differences in the proportion of animals affected by these alterations were found between the two infection groups. In contrast, the proportion of animals displaying β-APP accumulation was significantly higher in the T. canis than T. cati group as from 28 dpi regarding the cerebrum as well as at 98 dpi regarding the cerebellum. In T. canis-infected mice, myelinophagic microglia/macrophages ("gitter cells") appeared as from 14 dpi, whereas these were first observed at 70 dpi in T. cati-infected animals. The proportion of animals displaying demyelination and/or gitter cells in the cerebrum was significantly higher in the T. canis than T. cati group as from 28 dpi, and at 28 and 42 dpi regarding the cerebellum. Earlier and more severe neurodegeneration during T. canis- than T. cati-induced NT, especially in the cerebrum, may explain the differences in behavioural alterations observed in previous studies. In addition to differences in larval migration preferences, immunological processes may contribute to these patterns, which warrant further investigation.

Neuroinvasion of Toxocara canis- and T. cati-larvae mediates dynamic changes in brain cytokine and chemokine profile

Background

Neurotoxocarosis (NT) is induced by larvae of the dog or cat roundworm (Toxocara canis or T. cati) migrating and persisting in the central nervous system of paratenic hosts, including humans, and may be accompanied by severe neurological symptoms. Host- or parasite-induced immunoregulatory processes contribute to the pathogenesis, but detailed data on pathogenic mechanisms and involvement of signalling molecules during cerebral Toxocara species infections are scarce.

Methods

To elucidate alterations in immunomodulatory mediator pattern, comprehensive multiplex bead array assays profiling comprising 23 different cytokines and chemokines were performed during the course of T. canis- and T. cati-induced NT. To this end, cerebra and cerebella of experimentally infected C57Bl/6 J mice serving as paratenic host models were analysed at six different time points (days 7, 14, 28, 42, 70 and 98) post infectionem (pi).

Results

Brain-body mass ratios of T. canis and T. cati-infected mice were significantly lower than those of the uninfected control group at day 14 pi, and also at day 28 pi for T. canis-infected mice. Both infection groups showed a continuous decrease of pro-inflammatory cytokine concentrations, including TNF-α, IFN-γ, GM-CSF and IL-6, in the cerebrum over the course of infection. Additionally, T. canis but not T. cati-induced neurotoxocarosis was characterised by significantly elevated levels of anti-inflammatory IL-4 and IL-5 in the cerebrum in the acute and subacute phase of the disease. The higher neuroaffinity of T. canis led to a prominent increase of eotaxin and MIP-1α in both the cerebrum and cerebellum, while in T. cati-infected mice, these chemokines were significantly elevated only in the cerebellum.

Conclusions

The direct comparison of T. canis- and T. cati-induced NT provides valuable insights into key regulatory mechanisms of Toxocara species in paratenic hosts. The cerebral cyto-/chemokine milieu is shifted to a predominantly anti-inflammatory immune response during NT, possibly enabling both survival of the parasite and the neuroinfected paratenic host. Alteration of eotaxin and MIP-1α concentrations are congruent with the higher neuroaffinity of T. canis and species-specific tropism of T. canis to the cerebrum and T. cati to the cerebellum.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1537-x) contains supplementary material, which is available to authorized users.

Comparative bioinformatic analysis suggests that specific dauer-like signalling pathway components regulate Toxocara canis development and migration in the mammalian host

Background

Toxocara canis is quite closely related to Ascaris suum but its biology is more complex, involving a phase of arrested development (diapause or hypobiosis) in tissues as well as transplacental and transmammary transmission routes. In the present study, we explored and compared dauer-like signalling pathways of T. canis and A. suum to infer which components in these pathways might associate with, or regulate, this added complexity in T. canis.

Methods

Guided by information for Caenorhabditis elegans, we bioinformatically inferred and compared components of dauer-like signalling pathways in T. canis and A. suum using genomic and transcriptomic data sets. In these two ascaridoids, we also explored endogenous dafachronic acids (DAs), which are known to be critical in regulating larval developmental processes in C. elegans and other nematodes, by liquid chromatography-mass spectrometry (LC-MS).

Results

Orthologues of C. elegans dauer signalling genes were identified in T. canis (n = 55) and A. suum (n = 51), inferring the presence of a dauer-like signalling pathway in both species. Comparisons showed clear differences between C. elegans and these ascaridoids as well as between T. canis and A. suum, particularly in the transforming growth factor-β (TGF-β) and insulin-like signalling pathways. Specifically, in both A. suum and T. canis, there was a paucity of genes encoding SMAD transcription factor-related protein (daf-3, daf-5, daf-8 and daf-14) and insulin/insulin-like peptide (daf-28, ins-4, ins-6 and ins-7) homologues, suggesting an evolution and adaptation of the signalling pathway in these parasites. In T. canis, there were more orthologues coding for homologues of antagonist insulin-like peptides (Tc-ins-1 and Tc-ins-18), an insulin receptor substrate (Tc-ist-1) and a serine/threonine kinase (Tc-akt-1) than in A. suum, suggesting potentiated functional roles for these molecules in regulating larval diapause and reactivation. A relatively conserved machinery was proposed for DA synthesis in the two ascaridoids, and endogenous Δ4- and Δ7-DAs were detected in them by LC-MS analysis. Differential transcription analysis between T. canis and A. suum suggests that ins-17 and ins-18 homologues are specifically involved in regulating development and migration in T. canis larvae in host tissues.

Conclusion

The findings of this study provide a basis for functional explorations of insulin-like peptides, signalling hormones (i.e. DAs) and related nuclear receptors, proposed to link to development and/or parasite-host interactions in T. canis. Elucidating the functional roles of these molecules might contribute to the discovery of novel anthelmintic targets in ascaridoids.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3265-y) contains supplementary material, which is available to authorized users.

Abnormal neurobehaviour and impaired memory function as a consequence of Toxocara canis- as well as Toxocara cati-induced neurotoxocarosis

BACKGROUND

Neuroinvasive larvae of the worldwide occurring zoonotic roundworms Toxocara canis and T. cati may induce neurotoxocarosis (NT) in humans, provoking a variety of symptoms including cognitive deficits as well as neurological dysfunctions. An association with neuropsychological disorders has been discussed. Similar symptoms have been described in T. canis-infected mice, whereas data on T. cati-induced NT are rare. Therefore, it was aimed to obtain insights into the impact on neurobehaviour as well as progression of neurological symptoms and behavioural alterations during the course of NT directly comparing T. canis- and T. cati-infected mice as models for human NT.

METHODOLOGY/PRINCIPAL FINDINGS

C57BL/6 mice were orally infected with 2000 embryonated T. canis or T. cati eggs, respectively, the control group received tap water. Mice were screened weekly for neurobehavioural alterations and memory function starting one day prior infection until 97 days post infection (pi; T. canis-infection) and day 118 pi (T. cati-infection, uninfected control). Mostly motoric and neurological parameters were affected in T. canis-infected mice starting day 20 pi with severe progression accompanied by stereotypical circling. In contrast, T. cati-infected mice mostly showed reduced response to sudden sound stimulus (indicator for excitability) and flight behaviour starting day 6 pi. Interestingly, enhanced grooming behaviour was observed exclusively in T. cati-infected mice, indicating a possible role of neurotransmitter dysregulation. Reduced exploratory behaviour and memory impairment was observed in both infection groups with delayed onset and less severe progression in T. cati- compared to T. canis-infected mice.

CONCLUSIONS/SIGNIFICANCE

Results highlight the need to consider T. cati beside T. canis as causative agent of human NT. Findings provide valuable hints towards differences in key regulatory mechanisms during T. canis- and T. cati-induced NT, contributing to a comprehensive picture and consequently a broader understanding of NT, which will aid in developing strategies towards prevention in addition to novel diagnostic and therapeutic approaches.

Global toxocariasis research trends from 1932 to 2015: a bibliometric analysis

BACKGROUND

Toxocariasis is a highly prevalent parasitic disease in the tropical regions of the world, with its impact on public health being typically underestimated. To better recognise the trends and characteristics of toxocariasis research, this study is a bibliometric analysis of the global toxocariasis research.

METHODS

Searches were completed on April 5, 2016, using the Scopus database. A search without any language restriction was performed to extract publications dealing with toxocariasis. Terms related to toxocariasis were used to perform a title keyword search.

RESULTS

A total of 2765 publications comprising 11 document types and published between 1932 and 2015 were included in the analysis. Articles were the most popular document form, accounting for 83.62% of all publications, followed by letters (3.80%) and reviews (3.4%). The annual number of research publications increased from 30 in 1980 to 111 in 2015, indicating that the number of publications on toxocariasis has increased slowly over the past 35 years. The United States of America and Japan are the predominant countries of origin, with 303 articles and 207 articles, respectively, followed by Brazil and the United Kingdom, with 180 (6.5%) each. The h-index for all the publications was 60. The highest h-index were for publications from the United Kingdom (h-index value = 43) and the United States (h-index value = 39); these two countries were also involved with the highest number of international collaborations, with 27 and 28 countries, respectively.

CONCLUSIONS

Developed countries, including the United States, Japan, the United Kingdom, France, Germany and Italy, are the world's leaders in toxocariasis research, contributing to more than 34% of the total published literature. In addition, developing countries, such as Brazil, Poland, Argentina and India, showed a noticeable increase in published papers on toxocariasis research in recent years. A push for more collaboration is needed to achieve a superior research strategy related to toxocariasis at the global level from the viewpoint of epidemiological data, clinical aspects, medical ecology, molecular aspects and treatment practices associated with toxocariasis.

Harnessing the Toxocara Genome to Underpin Toxocariasis Research and New Interventions

Parasitic worms, such as flatworms (platyhelminths) and roundworms (nematodes), cause substantial morbidity and mortality in animals and people globally. The ascaridoid nematode Toxocara canis is a zoonotic parasite of socioeconomic significance worldwide. In humans, this worm causes toxocariasis (disease) mainly in underprivileged communities in both the developed and developing worlds. While reasonably well studied from clinical and epidemiological perspectives, little is understood about the molecular biology of T. canis, its relationship with its hosts and the disease that it causes. However, a recent report of the draft genome and transcriptomes of T. canis should underpin many fundamental and applied research areas in the future. The present article gives a background on Toxocara and toxocariasis, a brief account of diagnostic approaches for specific identification and genetic analysis, and gives a perspective on the impact that the genome of T. canis and advanced molecular technologies could have on our understanding of the parasite and the diseases that it causes as well as the design of new and improved approaches for the diagnosis, treatment and control of toxocariasis.

Knowledge gaps in the epidemiology of Toxocara: the enigma remains

Toxocara species infect a wide range of companion, domestic and wild animals as definitive and paratenic hosts, via multiple routes of transmission, producing long-lived tissue-inhabiting larvae and resistant eggs that can survive in the external environment. Therefore Toxocara and the disease it causes in humans, toxocariasis, represents an ideal aetiological agent for the development of the one health approach. However, despite increasing awareness of the public health significance of toxocariasis, gaps in our understanding of certain key aspects of the parasite's biology and epidemiology remain. These gaps hinder our ability to integrate research effort within the veterinary, medical and environmental disciplines. This review will highlight key deficits in our understanding of nine dimensions of Toxocara epidemiology and discuss a potential scenario to develop a more integrated, one health approach to improve our understanding of the prevention and control of this complex and cryptic zoonosis.

Effects of Toxocara larvae on brain cell survival by in vitro model assessment

Neuroinvasive larvae of the common dog and cat roundworms, Toxocara canis and Toxocara cati, may cause severe neurological and neuropsychological disturbances in humans. Despite their pathogenic potential and high prevalence worldwide, little is known about their cell-specific influences and cerebral host-pathogen interactions in neurotoxocarosis. To address this discrepancy, a co-culture system of viable larvae with murine neuronal (CAD), oligodendrocytal (BO-1) and microglial (BV-2) cell lines has been established. Additionally, murine adult brain slices have been co-cultured with Toxocara larvae to consider complex organotypic cell-cell interplay. Cytotoxicity of larval presence was measured enzymatically and microscopically. Microscopic evaluation using trypan blue exclusion assay revealed to be less reliable and sensitive than the lactate dehydrogenase activity assay. Ultimately, even low numbers of both T. canis and T. cati larvae have impaired survival of differentiated CAD cells, which morphologically resemble primary neurons. In contrast, viability of oligodendrocytal and microglial cells as well as brain slices was not impaired by larval presence. Therefore, immune-mediated mechanisms or trauma by migrating larvae presumably induce the in vivo pathology rather than acute cytotoxic effects. Conclusively, the helminthic larvae co-culture system presented here is a valuable in vitro tool to study cell-specific effects of parasitic larvae and their products.