Longitudinal myelitis caused by visceral larva migrans associated with Toxocara cati infection: case report

Toxocara cati Infection in Cats (Felis catus): A Systematic Review and Meta-Analysis

Introduction: Toxocariasis is an infection caused in canines, felines, humans, and other vertebrates by species of the genus Toxocara, such as T. canis and T. cati. The embryonated eggs of these parasites are the primary means of acquiring the infection for both definitive hosts, dogs and cats, respectively, and for intermediates, such as humans and other vertebrates. When deposited on park soils, environmental contamination becomes a risk to environmental, human, and animal health. Objective: To determine the global prevalence of Toxocara cati in cats (Felis catus). Methods: A systematic review of the literature was carried out in six databases (Scopus, PubMed, ScienceDirect, SciELO and Google Scholar) to evaluate the global prevalence of Toxocara cati in cats, defined by coproparasitological, histological, and molecular techniques. A meta-analysis was performed using a random effects model to calculate pooled prevalence and 95% confidence intervals (95% CI). A two-tailed 5% alpha level was used for hypothesis testing. Results: Two hundred and eighty-nine studies were included. The global pooled prevalence of Toxocara cati in cats using coproparasitological methods was 17.0% (95.0% CI: 16.2-17.8%). In the subgroup analysis according to country, Nepal had the highest prevalence of T. cati infection (94.4%; 95% CI 89.7-99.2%). The pooled prevalence of T. cati infection by PCR in four studies was 4.9% (95.0% CI: 1.9-7.9%). Conclusions: This systematic review underscores the need for preventive action against toxocariasis due to its widespread prevalence. The interplay between animal and human health should be emphasised, necessitating measures like deworming cats, hygiene practices, and public education to mitigate risks. Safeguarding feline health can also reduce human transmission, benefiting both species.

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.

Clinical spectrum of symptoms in cerebral Toxocariasis (Review)

Human helminth zoonosis is one of the most encountered helminthiases worldwide. Representative diseases include Toxocara canis and Toxocara cati, which are common nematodes prevalent in dogs and cats. The infiltration of these roundworms in the human body through contaminated food or nematode eggs could lead to central nervous system injury as the roundworms can cross the blood-brain barrier leading to neurotoxocariasis. Among the neurological and neuropsychological disturbances produced by Toxocara infection, in humans, the most representative are meningitis, encephalitis, myelitis and cerebral vasculitis, but asymptomatic central nervous system infection is probably the most prevalent. The present review examines the clinical symptomatology of neurotoxocariasis in case reports in the literature in the last 7 decades (1950-2020). The available evidence was retrieved from PubMed and Medline electronic databases. The present review reports the most prevalent clinical symptomatology in the cases of detected and diagnosed Toxocara infection with neuroinvasion. Thus, the present review aims to raise the awareness of neurological cases of Toxocara infection with the potential to at least establish differential diagnosis of neurotoxocariasis.

Toxocariasis of the Nervous System

PURPOSE

Toxocariasis is a helminthozoonosis caused by the infection of a human host by the larva of Toxocara spp., predominately involving Toxocara canis and Toxocara cati, which are common nematodes in dogs and cats, respectively. Human transmission occurs through contact with animals or by consumption of food contaminated with parasite's eggs. The purpose of this article is to review the current knowledge regarding human neurotoxocariasis.

METHODS

We conducted a systematic review of the existing literature concerning toxocariasis of the nervous system.

RESULTS

Clinical spectrum of human toxocariasis varies widely from a subclinical course to significant organ morbidity. Clinical course depends on parasitic load, the migration route of the larvae and host response. Human neurotoxocariasis is a relatively rare entity yet associated with severe sequelae. Manifestations include meningitis (usually eosinophilic), encephalitis, myelitis, cerebellar vasculitis, space-occupying lesion, behavioral abnormalities, and optic neuritis. Even though valid diagnostic criteria are lacking, neurotoxocariasis should be suspected in patients with neurologic symptoms and cerebrospinal fluid (CSF) pleocytosis with eosinophilia, positive serology for anti-Toxocara antibodies, in serum and/or CSF, sterile CSF and clinical improvement after antihelminthic treatment. Neurotoxocariasis is treated by benzimidazole components, most frequently albendazole, corticosteroids, or diethylcarbamazine.

CONCLUSION

Parasite larvae migrate through tissues and are able to reach the nervous system causing neurotoxocariasis. Its clinical spectrum varies and includes myelitis, meningoencephalitis, brain abscess, and vasculitis. Neurotoxocariasis should always be suspected in patients with neurologic symptoms accompanied by eosinophilia in blood and/or CSF. Early diagnosis and treatment could prevent long-term neurologic impairment.

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.

Seroprevalence of human toxocarosis in Europe: A review and meta-analysis

Toxocarosis is distributed worldwide and represents the most prevalent zoonotic helminth infection in industrialized countries, thereby posing a substantial risk for public health. Thus, toxocarosis is one of CDC's Neglected Parasitic Infections that has been targeted for public health action. This systematic review and meta-analysis summarizes Toxocara seroprevalence in general populations from Europe, populations suspected of Toxocara infection and defined risk groups. Random-effects meta-analysis of proportions based on 41 publications resulted in an overall seroprevalence of 6.2% (95% CI: 4.7-8.3%) in the general population of Europe. Subgroup analysis according to decades (1970-2010s) revealed a significant increase in seroprevalence, with the highest value (12.4%; 95% CI: 6.5-22.3%) in the 2010s (χ²=17.87, df=4, P=0.001). There were no significant differences between pooled prevalence rates of European sub-regions (χ²=3.01, df=3, P=0.389). Furthermore, meta-analysis of seroprevalence according to age groups, based on data from 22 publications, indicated a significantly higher pooled seroprevalence of 14.9% (95% CI: 8.5-24.8%) in people more than 50 years of age than in younger age cohorts (χ²=8.33, df=2, P=0.016). Occupational groups exposed to contaminated soil and infected animals bear substantial risk for acquiring Toxocara infection. Due to the close link between animal infection and human Toxocara exposure, a "One Health" approach for the prevention of Toxocara infection in both humans and animals is required.

Toxocara infection in the differential diagnosis of multiple sclerosis in the Middle East

A critical step in the diagnosis of multiple sclerosis is to rule out a heterogeneous variety of multiple sclerosis mimickers, which is crucial in the era of powerful immune-modulator treatments. In this review, we discuss the background of toxocariasis in general, present central nervous system Toxocara infection as one of the multiple sclerosis mimickers in the Middle East, and share our experience about the diagnosis and management of this condition. This entity seems very relevant in a region such as the Middle East, where displacement of populations and conflict can result in non-hygienic food and water management bundles. The diagnosis should be entertained, especially when assessing patients with myelopathy. The presence of a single lesion in the spinal cord with inflammatory features should prompt serological testing for Toxocara IgG and IgM in serum and the cerebrospinal fluid. This infection is treatable, with the regimen of high-dose albendazole being one of the most accepted treatments. Although most cases exhibit a good prognosis, some have residual deficits localized to the affected spinal cord level.

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.

Clinical and Magnetic Resonance Imaging Findings of Neurotoxocariasis

Human toxocariasis is one of the most prevalent helminthiases worldwide. Toxocara canis larvae can cross the blood-brain barrier leading to the neurotoxocariasis. The clinical presentation consists of a wide spectrum of neurological manifestations, but asymptomatic infection is probably common. Neurotoxocariasis is not a frequent diagnosis probably due to the non-specific nature of its symptoms as well as the lack of confirmatory diagnostic tests. Diagnosis of neurotoxocariasis is based on the presence of a high titer of anti-Toxocara antibody in the cerebrospinal fluid or in the serum, presence of eosinophilia in the serum or cerebrospinal fluid, and clinical and radiological improvement after anthelmintic therapy; however, universally accepted diagnostic criteria are lacking. Magnetic resonance imaging (MRI) findings include single or multiple, subcortical, cortical or white matter hyperintense lesions, best visualized on FLAIR and T2-weighted imaging, and usually isointense or hypointense on T1. These imaging findings are suggestive but not specific to neurotoxocariasis. Definitive diagnosis is made by histological confirmation, but it is rarely followed. This review provides an overview of the clinical manifestations, management options, and MRI findings of neurotoxocariasis.

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.

Neurotoxocariasis: a systematic literature review

PURPOSE

Toxocariasis is a widespread zoonosis, which may result in central nervous system injury.

METHODS

We conducted a systematic literature review in MEDLINE, SciELO, ScienceDirect and Google Scholar up to April 2015 using a combination of the following search terms: "neurotoxocariasis" or "neurotoxocarosis", "toxocariasis" or "toxocarosis" and "cerebral" or "neurologic".

RESULTS

One hundred cases of neurotoxocariasis were identified in literature. The majority of patients were male (58 %), with a median age of 42 years. The predominant clinical pictures were myelitis (60 %), encephalitis (47 %) and/or meningitis (29 %). Fever was inconstant (23 %). The suspected mode of transmission, mentioned in only 49 % of cases, was mainly contact with dogs and/or cats (67 %) and ingestion of contaminated food (31 %). Diagnostic imaging examinations found hypodense lesions in cerebral scanner sequences and hyperintense lesions in cerebral MRI T2-weighted sequences in 65 and 57 % of encephalitis cases respectively, and in 92 % of myelitis cases in medullary MRI T2-weighted sequences. The detection of antibodies against Toxocara spp. was almost constant in blood and cerebrospinal fluid (CSF), 99 and 93 %, respectively. The two most commonly used drugs were corticosteroids (72 %) and/or albendazole (68 %) for a period of at least 3 weeks, which often needed to be repeated. Despite a low mortality rate (6 %), complete remission was observed in only 40 % of cases.

CONCLUSIONS

Neurotoxocariasis, a completely preventable zoonosis, could lead to severe sequelae failing prompt diagnosis. A compatible clinical picture, presence of risk factors, blood eosinophilia and high titers of antibodies against Toxocara spp. in CSF should alert physicians.

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

Toxocara canis and Toxocara cati are globally occurring intestinal nematodes of dogs and cats with a high zoonotic potential. Migrating larvae in the CNS of paratenic hosts, including humans, may cause neurotoxocarosis resulting in a variety of neurological symptoms. Toxocara canis exhibits a stronger affinity to the CNS than T. cati, causing more severe neurological symptoms in the mouse model. Pathomechanisms of neurotoxocarosis as well as host responses towards the respective parasite are mostly unknown. Therefore, the aim of this study was to characterise the pathogenesis at a transcriptional level using whole genome microarray expression analysis and identify differences and similarities between T. canis- and T. cati-infected brains. Microarray analysis was conducted in cerebra and cerebella of infected C57Bl/6J mice 42daysp.i. revealing more differentially transcribed genes for T. canis- than T. cati-infected brains. In cerebra and cerebella of T. canis-infected mice, a total of 2304 and 1954 differentially transcribed genes, respectively, were identified whereas 113 and 760 differentially transcribed genes were determined in cerebra and cerebella of T. cati-infected mice. Functional annotation analysis revealed major differences in host responses in terms of significantly enriched biological modules. Up-regulated genes were mainly associated with the terms "immune and defence response", "sensory perception" as well as "behaviour/taxis" retrieved from the Gene Ontology database. These observations indicate a strong immune response in both infection groups with T. cati-infected brains revealing less severe reactions. Down-regulated genes in T. canis-infected cerebra and cerebella revealed a significant enrichment for the Gene Ontology term "lipid/cholesterol biosynthetic process". Cholesterol is a highly abundant and important component in the brain, representing several functions. Disturbances of synthesis as well as concentration changes may lead to dysfunction in signal transduction and neurodegenerative disease. Overall, only a minor overlap of differentially transcribed genes was observed between the two infection groups in both brain parts. Most genes are regulated individually in each infection group, supporting the evident differences of both roundworm species observed in the paratenic host in previous studies. In summary the present study underlines the differences in pathogenicity of T. canis and T. cati. It furthermore provides a comprehensive basis for future analyses over the course of infection as well as functional tests to identify gene regulatory circuits that are crucial for pathogenesis of neurotoxocarosis. The results of this study provide a promising foundation for further specific research to evaluate the particular pathogenetic mechanisms and to identify possible therapeutic targets.

Neurotoxocarosis: marked preference of Toxocara canis for the cerebrum and T. cati for the cerebellum in the paratenic model host mouse

Background

Infective larvae of the worldwide occurring zoonotic roundworm T. canis exhibit a marked affinity to the nervous tissues of paratenic hosts. In humans, most cases of neurotoxocarosis are considered to be caused by larvae of T. canis as T. cati larvae have rarely been found in the CNS in previous studies. However, direct comparison of studies is difficult as larval migration depends on a variety of factors including mouse strains and inoculation doses. Therefore, the present study aims to provide a direct comparison of both roundworm species in mice as a model for paratenic hosts with specific focus on the CNS during the acute and chronic phase of disease to provide a basis for further studies dealing with neurotoxocarosis.

Methods

C57Bl/6J mice were infected with 2000 embryonated T. canis and T. cati eggs, respectively as well as Balb/c mice infected with T. cati eggs only. On 8 time points post infection, organs were removed and microscopically examined for respective larvae. Special focus was put on the CNS, including analysis of larval distribution in the cerebrum and cerebellum, right and left hemisphere as well as eyes and spinal cord. Additionally, brains of all infection groups as well as uninfected controls were examined histopathologically to characterize neurostructural damage.

Results

Significant differences in larval distribution were observed between and within the infection groups during the course of infection. As expected, significantly higher recovery rates of T. canis than T. cati larvae were determined in the brain. Surprisingly, significantly more T. canis larvae could be found in cerebra of infected mice whereas T. cati larvae were mainly located in the cerebellum. Structural damage in brain tissue could be observed in all infection groups, being more severe in brains of T. canis infected mice.

Conclusions

The data obtained provides an extensive characterization of migrational routes of T. canis and T. cati in the paratenic host mouse in direct comparison. Even though to a lesser extent, structural damage in the brain was also caused by T. cati larvae and therefore, the potential as pathogenic agents should not be underestimated.