Toxocara canis infection: clinical and epidemiological associations with seropositivity in kindergarten children

Association between Alzheimer's disease and Toxocara infection/exposure: a case-control study

BACKGROUND

Infections may contribute to Alzheimer's disease (AD) risk. Limited evidence suggests Toxocara spp. infection/exposure could influence AD development.

METHODS

We investigated Toxocara seropositivity and AD in Iranian adults using a matched case-control study. Our sample included 90 AD cases and 91 healthy older adults. Anti-Toxocara immunoglobulin G (IgG) antibodies were assessed via enzyme-linked immunosorbent assay. We computed the odds ratios (ORs) and 95% confidence intervals (CIs) through univariable and multivariable analyses, adjusting for potential confounders.

RESULTS

There were 33/90 (36.67% [95% CI 26.75 to 47.48]) anti-Toxocara IgG seropositive individuals identified among the AD cases and 21/91 (23.07% [95% CI 14.89 to 33.09]) among the healthy controls. In univariable analysis, a significant association was identified between anti-Toxocara IgG seropositivity and AD (OR 1.93 [95% CI 1.01 to 3.69], p<0.001). Moreover, the association remained significant (OR 2.18 [95% CI 1.05 to 4.49], p<0.001) in multivariable analysis after adjustment for covariates. There was no association between anti-Toxocara IgG seropositivity and the severity of AD (OR 0.75 [95% CI 0.21 to 2.61], p=0.47).

CONCLUSIONS

Our findings indicated that Toxocara exposure/infection could be a potential risk factor for development of AD. To better understand a real causality between Toxocara exposure/infection and AD and related dementias, follow-up designed and adequately powered studies are needed.

A Study on the Monitoring of Toxocara spp. in Various Children's Play Facilities in the Republic of Korea (2016-2021)

Toxocara spp. is a zoonotic soil-transmitted parasite that infects canids and felids, which causes toxocariasis in humans, migrating to organ systems, including the lungs, the ocular system, and the central nervous system. Since Toxocara spp. is usually transmitted through soil, children tend to be more susceptible to infection. In order to monitor contamination with Toxocara spp. in children's play facilities in the Republic of Korea, we investigated 11,429 samples of soil from daycare centers, kindergartens, elementary schools, and parks across the country from January 2016 to December 2021. Since the Environmental Health Act in the Republic of Korea was enacted in March 2008, there have been sporadic reports of contamination by Toxocara spp. in children's activity zones. In this study, soil from children's play facilities in regions across the Republic of Korea was monitored according to the Korean standardized procedure to use it as basic data for preventive management and public health promotion. The national average positive rate was 0.16% (18/11,429), and Seoul showed a higher rate of 0.63% (2/318) than any other regions while Incheon, Daegu, Ulsan, Kangwon-do, Jeollabuk-do, and Jeollanam-do were negative (p < 0.05). The positive rates were as follows: 0.37% (4/1089) in daycare centers, 0.13% (3/2365) in kindergartens, 0.2% (7/4193) in elementary schools, 0.09% (1/1143) in apartments, and 0.14% (3/2198) in parks. In addition, it was confirmed that 0.2% (1/498) of elementary schools and 1.17% (2/171) of parks were re-contaminated among play facilities managed with the establishment of a regular inspection cycle. Consequently, there is an essential need for continuous monitoring of Toxocara spp. contamination and regular education for preschool and school children in order to prevent soil-borne parasite infections.

Canine and Feline Parasitology: Analogies, Differences, and Relevance for Human Health

Cats and dogs are treated as family members by most pet owners. Therefore, a high quality of veterinary care and preventive medicine is imperative for animal health and welfare and for the protection of humans from zoonotic pathogens. There is a general perception of cats being treated as "small dogs," especially in the field of clinical parasitology. As a result, several important differences between the two animal species are not taken into proper consideration and are often overlooked. Dogs and cats are profoundly different under evolutionary, biological, ethological, behavioral, and immunological standpoints. These differences impact clinical features, diagnosis, and control of canine and feline parasites and transmission risk for humans. This review outlines the most common parasitoses and vector-borne diseases of dogs and cats, with a focus on major convergences and divergences, and discusses parasites that have (i) evolved based on different preys for dogs and cats, (ii) adapted due to different immunological or behavioral animal profiles, and (iii) developed more similarities than differences in canine and feline infections and associated diseases. Differences, similarities, and peculiarities of canine and feline parasitology are herein reviewed in three macrosections: (i) carnivorism, vegetarianism, anatomy, genetics, and parasites, (ii) evolutionary adaptation of nematodes, including veterinary reconsideration and zoonotic importance, and (iii) behavior and immune system driving ectoparasites and transmitted diseases. Emphasis is given to provide further steps toward a more accurate evaluation of canine and feline parasitology in a changing world in terms of public health relevance and One Health approach.

Neurocognitive and neuropsychiatric effects of toxocariasis

Caused by the neuroinvasive nematodes Toxocara canis and Toxocara cati, human toxocariasis has a worldwide distribution with seroprevalence in humans associated with low socioeconomic status and low educational attainment. Third-stage Toxocara larvae can invade human tissues, including the brain and spine, where they can result in encephalitis, meningitis, and inflammation. Toxocara infection in animal models has been associated with cognitive and behavioural changes. In humans, preliminary cross-sectional research suggests that Toxocara seropositivity is associated with worse cognitive function in children and adults. Additional preliminary cross-sectional findings suggest associations between Toxocara seropositivity and neuropsychiatric function, including schizophrenia and neurologic conditions such as epilepsy. Given the widespread distribution of human toxocariasis and early evidence suggesting that it can be associated with cognitive and neuropsychiatric function in humans, additional research regarding the effects of toxocariasis on the human brain is required.

Seroepidemiology of human toxocariasis in North Africa

Seroprevalence studies on human toxocariasis help to assess the burden and the morbidity associated with this zoonosis. This review searched the seroprevalence studies and case reports in six North African countries: Algeria, Egypt, Libya, Morocco, Sudan and Tunisia, since 1990. The search also included studies on the environmental factors related to the risk of transmission. Most of the published epidemiological studies were done in Egypt. Cross-sectional and case-control studies in Egypt demonstrated that toxocariasis is a significant zoonosis that could be associated with conditions like bronchial asthma allergies and certain neuropsychiatric disorders. The population at risk of this infection includes all ages, both genders, in contact with dogs, resident in rural areas with poor housing conditions. The publications from Tunisia, Morocco and Algeria are limited to case reports and retrospective analyses of cases, but the disease is probably under-diagnosed in these three countries. There are no published reports on human toxocariasis in Libya and Sudan during the period covered by the review. Animal studies confirm high infection rates of dogs with Toxocara canis in North Africa. There is also evidence of wide-spread contamination of soil and water with Toxocara spp. eggs. Moreover, the use of untreated wastewater for irrigation in parts of North Africa could be a source of contamination of agricultural products with eggs of Toxocara spp. Population-based studies on human toxocariasis are recommended, using standardized diagnostic tests. These surveys should also assess risk factors to guide preventive measures.

Pathogenesis of cerebral toxocariasis and neurodegenerative diseases

Toxocara canis belongs to one of zoonotic parasites that commonly infects canines worldwide, and its eggs in host faeces may contaminate the food, water, soil and their fur as well as the larvae entrapped in the granuloma can infect paratenic hosts including mice and humans. Survivability of T. canis embryonated eggs under moist, cool conditions may be as long as 2-4 years or more. In paratenic hosts such as mice and humans, T. canis L3 larvae neither moult, grow, nor replicate and will wander through a number of internal organs in humans so as to cause Th2-dominant pathology in various internal organs as leading to neurotoxocariasis (NT), ocular toxocariasis (OT), or visceral larva migrans (VLM). Although the systemic immune response to T. canis has been widely reported, the immune response in the brain has received little attention. Differential cytokine expression and other brain injury-associated biomarkers or neurodegeneration-associated factors have been observed in infected versus uninfected outbred and inbred mice. Preliminary data have also suggested a possible link between significant memory impairment and cytokine production associated with T. canis infection in the hippocampus which has been long recognised as being responsible for learning and memory functions. Notably, it remains an enigma concerning cerebral invasion by T. canis larvae rarely induces a recognisable neurological syndrome or its involvement in neuropathological disorders in humans. Exploration of the relationship between host and parasite in the brain may elucidate the cryptic symptoms of human cerebral toxocariasis, with patients presenting with mental retardation, epilepsy, neurodegeneration and other central nervous system (CNS) disorders.

Frequency of Toxocariasis among Patients Clinically Suspected to Have Visceral Toxocariasis: A Retrospective Descriptive Study in Sri Lanka

Introduction

Human toxocariasis is caused by several species of the nematode Toxocara. Two common clinical syndromes are ocular and visceral larva migrans.

Objectives

To determine the Toxocara antibody positivity in clinically suspected VLM patients and to describe demographic factors and clinical manifestations of seropositive patients.

Methods

522 clinically suspected patients were studied between 1993 and 2014. Relevant data was gathered from referral letters. Serum samples were subjected to Toxocara antigen ELISA.

Results

Overall, seropositivity was 50.2% (262), of which 109 (40.8%) were positive at high level of Toxocara antibody carriage and 153 (58.4%) were positive at low levels. The seropositives ranged from 3 months to 70 years (mean = 7.8). Younger age group had higher levels of seropositivity and it was statistically significant. Majority of children under 5 years were seropositive (47.7%, n = 125). Seropositivity was common in males (55.3%, n = 145). Clinical manifestations of seropositives include lymphadenopathy (24.1%) skin rash (22.5%), dyspnoea (21.7%), fever (21%), hepatosplenomegaly (9.2%), and abdominal pain (3.8%). 197 (75.2%) seropositive cases had eosinophilia. These symptoms were not statistically significant.

Conclusions

This study confirms toxocariasis as an important cause of childhood ill health identifying common clinical symptoms recommending preventive measures to limit transmission.

Cerebral Toxocariasis: Silent Progression to Neurodegenerative Disorders?

Toxocara canis and T. cati are highly prevalent nematode infections of the intestines of dogs and cats. In paratenic hosts, larvae do not mature in the intestine but instead migrate through the somatic tissues and organs of the body. The presence of these migrating larvae can contribute to pathology. Toxocara larvae can invade the brains of humans, and while case descriptions of cerebral toxocariasis are historically rare, improved diagnosis and greater awareness have contributed to increased detection. Despite this, cerebral or neurological toxocariasis (NT) remains a poorly understood phenomenon. Furthermore, our understanding of cognitive deficits due to toxocariasis in human populations remains particularly deficient. Recent data describe an enhanced expression of biomarkers associated with brain injury, such as GFAP, AβPP, transforming growth factor β1 (TGF-β1), NF-L, S100B, tTG, and p-tau, in mice receiving even low doses of Toxocara ova. Finally, this review outlines a hypothesis to explore the relationship between the presence of T. canis larvae in the brain and the progression of Alzheimer's disease (AD) due to enhanced AD-associated neurodegenerative biomarker expression.

Toxocariasis: seroprevalence in abandoned-institutionalized children and infants

Toxocariasis is an infection that has worldwide distribution. Toxocara canis is the most relevant agent due to its frequent occurrence in humans. Soil contamination with embryonated eggs is the primary source of T. canis. This study aimed to determine the seroprevalence of toxocariasis in 10-month to 3 year-old abandoned infants, considered to be at high risk because of their orphanhood status and early age. Blood samples were collected from 120 children institutionalized in an orphanage in the city of La Plata. In this study, we observed 38.33% of seropositive cases for T. canis by ELISA and 45% by Western blot techniques; significant differences among groups A (<1 year), B (1-2 years) and C (>2 years) were also found. In research group A, children presented a seropositivity rate of 23.91%, in group B of 42.85% and in group C of 56%, which indicates an increase in frequency as age advances, probably because of greater chances of contact with infective forms of the parasite since canines and soil are frequently infected with T. canis eggs. Abandoned children come from poor households, under highly unsanitary conditions resulting from inadequate or lack of water supply and sewer networks, and frequent promiscuity with canines, which promotes the occurrence of parasitic diseases. These children are highly vulnerable due to their orphanhood status and age.

Epidemiological situation of toxocariasis in Iran: meta-analysis and systematic review

Toxocariasis is the clinical terms applied to infection of human with ascarid nematodes in the order Ascaridida, named toxocara canis and toxocara cati. It is transmitted from dog and cat to humans. Accidental ingestion of parasite eggs causes ocular and visceral larva migrans in human. The aim of this study is to study epidemiology of toxocariasis in Iran using meta-analysis and systematic review. Using main key words of toxocariasis including epidemiology, Toxocara spp. Iran, dog and cat in databases such as SID, Google scholar, Pubmed, Magiran and Iranmedex, a number of 50 articles was extracted. A number of 27 articles of them were eligible for meta-analysis. Data extracted from articles and archived in excel software for analysis. Variance of each study obtained using binomial distribution. Heterogeny of studies surveyed using Cochrans Q test. Data analyzed using Random Effect Model test. Overall prevalence of toxocariasis obtained 21.6% in Iran. In total of 27 articles, 6911 samples including 1543 carnivores, (13 articles), 4569 human sera (10 articles) and 799 soil samples (4 articles) has been investigated. Seropositivity for human toxocariasis 15.8% (95%CI, 9.2-22.5), soil contamination for Txocara spp. eggs 21.6% (95%CI,-1.6-44.8) and dogs and cats infections with adult worm 26.8% (95%CI, 18.7-36.8) was obtained. Results of this study show that prevalence of toxocariasis has a growing trend in Iran. It could be decreased using education, culture making and giving information to people.

The significance of cerebral toxocariasis: a model system for exploring the link between brain involvement, behaviour and the immune response

Toxocara canis is a parasitic nematode that infects canines worldwide, and as a consequence of the widespread environmental dissemination of its ova in host faeces, other abnormal hosts including mice and humans are exposed to infection. In such abnormal or paratenic hosts, the immature third-stage larvae undergo a somatic migration through the organs of the body but fail to reach maturity as adult worms in the intestine. The presence of the migrating larvae contributes to pathology that is dependent upon the intensity of infection and the location of the larvae. A phenomenon of potential public health significance in humans and of ecological significance in mice is that T. canis larvae exhibit neurotrophic behaviour, which results in a greater concentration of parasites in the brain, as infection progresses. Toxocara larval burdens vary between individual outbred mice receiving the same inocula, suggesting a role for immunity in the establishment of cerebral infection. Although the systemic immune response to T. canis has been widely reported, the immune response in the brain has received little attention. Differential cytokine expression and other brain injury-associated biomarkers have been observed in infected versus uninfected outbred and inbred mice. Preliminary data have also suggested a possible link between significant memory impairment and cytokine production associated with T. canis infection. Mice provide a useful, replicable animal model with significant applicability and ease of manipulation. Understanding the cerebral host-parasite relationship may shed some light on the cryptic symptoms of human infection where patients often present with other CNS disorders such as epilepsy and mental retardation.

Pet roundworms and hookworms: a continuing need for global worming

Ascarids and ancylostomatids are the most important parasites affecting dogs and cats worldwide, in terms of diffusion and risk for animal and human health. Different misconceptions have led the general public and pet owners to minimize the importance of these intestinal worms. A low grade of interest is also registered among veterinary professions, although there is a significant merit in keeping our guard up against these parasites. This article reviews current knowledge of ascarids and ancylostomatids, with a special focus on pathogenicity, epidemiology and control methods in veterinary and human medicine.

Biochemical and immunopathological changes in experimental neurotoxocariasis

Toxocariasis is a widespread soil-transmitted parasitic disease. Toxocara canis larvae migrate through the tissues with a special predilection for the central nervous system. Recently, neurotoxocariasis is being diagnosed in humans with increasing frequency due to improved diagnostic tools. The present study aimed at exploring the biochemical and immunopathological alterations in the brain in experimental T. canis infection. For this purpose, 75 Toxocara-infected mice were sacrificed at 2, 5, and 16 weeks post-infection. The brains were removed and assayed for total larval count, pro-inflammatory cytokines (TNF-alpha, IL-6), and central neurotransmitters (gamma-aminobutyric acid, glutamate, dopamine, norepinephrine, and serotonin). Brain sections were also stained for histopathological study, and for assessment of the expression of inducible nitric oxide synthase (iNOS), and glial fibrillary acidic protein (GFAP) by immunohistochemical methods. We found that larval recovery showed progressive increase over the course of infection. Furthermore, the infected mice displayed increased expression of pro-inflammatory cytokines and iNOS, as well as significant disturbances in neurotransmitter profile. Astrocytic activation, evidenced by enhanced expression of GFAP, was also manifest in infected animals. These changes were maximal in the chronic stage of infection or intensified over time. In conclusion, experimental neurotoxocariasis is associated with significant biochemical, immunological, and pathological changes.

Developmental age, physical fitness andToxocaraseroprevalence amongst lower-secondary students living in rural areas contaminated withToxocaraeggs

Scarce and inconclusive information on general biological impact ofToxocarainvasion on paratenic hosts, and people in particular, has led us to undertake a comprehensive study of the problem. The study has been conducted in a rural environment, which is considered a toxocarosis risk factor. In total 200 soil samples have been screened forToxocaraeggs by flotation, of which 14·5% were positive. Backyards close to households were most heavily contaminated with infectious eggs – 21·7% of positive samples. ELISA serological tests performed on 242 lower-secondary students found 14·5% of the studied population to be definitely positive – 16·5% of boys and 12·8% of girls, respectively. The odds of being infected withToxocarawere 2 times (CI: 1·15–3·85) more likely for individuals who owned a cat than those who did not own a cat. Strong significant correlation between seropositivity and the presence of a dog in a household was found with boys. The level of developmental age was significantly higher in seropositive than in seronegative students. No significant correlation has been observed between the motor abilities and seropositivity of students. Seropositive boys had significantly lower end-of-year grades than their seronegative counterparts.

Possible intrafamilial transmission of Toxocara causing eosinophilic meningitis in an infant

Human toxocariasis can result from the inadvertent ingestion of embryonated eggs of Toxocara canis or Toxocara cati from environmental sources such as dirt, sand, or foods carrying contaminated soil. We report a case in an infant resulting in eosinophilic meningitis and prolonged fever. The case illustrates probable intrafamilial transmission, a mode of transmission that has not been previously documented.

Neurotoxocarosis

Infection of humans with embryonated eggs of Toxocara canis (larva migrans) remains asymptomatic, or results in covert or common toxocarosis, visceral larva migrans syndrome, or ophthalmologic and neurologic impairment. Though neurological manifestations of Toxocara canis larvae are rare, toxocarosis remains an important differential diagnosis of various neurological disorders. Manifestations of the central nervous system are dementia, meningo-encephalitis, myelitis, cerebral vasculitis, epilepsy, or optic neuritis. Manifestations of the peripheral nervous system comprise radiculitis, affection of cranial nerves, or musculo-skeletal involvement. If toxocarosis is neglected, ignored, or refused as a differential of these abnormalities, it may be easily overlooked for years. Early recognition and treatment of the infection is, however, of paramount importance since it reduces morbidity and mortality and the risk of secondary superinfection. Like the visceral manifestations, neurological manifestations of toxocarosis are treated by benzimidazole components, most frequently albendazole, corticosteroids, or diethylcarbamazine. If detected and treated early, the prognosis of neurological manifestations of toxocarosis is favourable.

Frequency and risk factors for toxocariasis in children from a pediatric outpatient center in southeastern Brazil

To estimate the frequency of anti-Toxocara sp. antibodies, and evaluate factors associated with this infection, sera from 242 male and female children, aged from one to fifteen years old, attended at the Hospital of the Federal University of Uberlândia, Minas Gerais State, Brazil, were analyzed by ELISA. Information on the patients was collected and registered using an investigative questionnaire, and details on possible clinical alterations were obtained from the medical charts of 187 patients. Of a total of 242 samples, 21 (8.7%) were positive for anti-Toxocara sp. antibodies. The presence of dogs and cats and the school variable (place of contact), appeared to be significantly associated (p < 0.05) with a positive serology. Respiratory symptoms and eosinophil counts greater than 20% also showed a positive statistical correlation with a positive serology for Toxocara sp.. Factors such as sex and age, and symptoms like headache, stomach ache, convulsive crises and anemia were not associated with toxocariasis.

Prevalence of Toxocara cati and other parasites in cats’ faeces collected from the open spaces of public institutions: Buenos Aires, Argentina

Toxocarosis is a worldwide parasitic infection that affects both cats and dogs. Toxocara cati (Schrank, 1788) syn. Toxocara mystax (Zeder, 1800) prevalence was studied in faeces from stray cats collected from the open spaces of public institutions of Buenos Aires city, both building and surrounding open spaces are fenced off. Of the 465 samples obtained from March to June of 2005, 58.3% were found to have parasite eggs. The following parasites were identified from the 271 positive samples: T. cati (61.2%), Cystoisospora spp. (20.3%), Trichuris spp. (17.0%), Toxascaris leonina (15.1%), Ancylostoma spp. (14%) and Aelurostrongylus abstrusus (2.6%). T. cati prevalence was 35.7% (95% confidence interval: 31.2-40.1), with a 42.2% single isolations. The most frequent combination was T. cati and Cystoisospora spp. (9%). More than half the areas studied showed over 40% prevalence. Seventy-one percent of the collected samples were fresh with a variable moist consistency and 29% were older with a dry consistency. A statistically significant association was found between sample consistency and presence of parasites (chi2 = 10.81; p = 0.001) as also between sample consistency and presence of T. cati (chi2 = 11.27; p = 0.0007). Moist consistencies were significantly different from the rest: consistency (wet or dry) versus parasites (z = 1.95; p = 0.02) (95% confidence interval: 0.004-0.203); consistency (wet or dry) versus T. cati (z = 3.25; p = 0.0006) (95% confidence interval: 0.075-0.254). The cat population that inhabits these public green spaces contaminates the environment, thus transforming them into dangerous spaces with a variable rate for the human population that spends time in these places.

Visceral larva migrans presenting as acute abdomen in a child

An unusual presentation of visceral larva migrans observed in a patient is reported. A 5-year-old boy suffering fever, abdominal pain, tenderness, and rigidity in the right lower and upper quadrant of the abdomen was operated on, with the false diagnosis of acute abdomen, and exploratory surgery was carried out. The pathological examination of the liver biopsy revealed eosinophil-rich necrotizing granulomatous inflammation with Toxocara spp larva. The diagnosis was also confirmed by serologic results. Clinicians should remember that toxocaral visceral larva migrans may rarely mimic an acute abdomen and cause unnecessary operations.

A murine model for cerebral toxocariasis: characterization of host susceptibility and behaviour

Toxocara canis, the parasitic roundworm of dogs, can infect a number of paratenic hosts, such as mice and humans, due to the widespread dissemination of its ova in the environment. In these paratenic hosts, larvae have been shown to exhibit a predilection for the central nervous system, resulting in an increasing number of parasites migrating to the brain as infection progresses. In an initial experiment, we investigated the differential brain involvement of T. canis in 7 strains of inbred mice, and chose 2 strains, susceptible (BALB/c) and resistant (NIH) to cerebral infection. In a second experiment, both strains were investigated in terms of course of migration, larval accumulation, and behavioural response to T. canis infection. Results revealed that infected BALB/c mice took significantly longer to drink from a water source (following a period of deprivation), compared with control mice, indicating some degree of memory impairment. Cerebral larval recoveries from both strains of mice demonstrated variation between the two experiments, suggesting that larval burdens may not be a reliable indicator of susceptibility or resistance to T. canis infection. The percentage of total recovered larvae in each organ may be a better representation of larval distribution. Our model system may provide insights into the impact of chronic geohelminth infection on cognitive development.

Seroprevalence of toxocariasis in Lebanon: a pilot study

Toxocariasis is a common helminthic infection that has a worldwide distribution. However, data from Lebanon about the prevalence of this infection are non-existent. We conducted a Toxocara seroprevalence study with 150 subjects attending the outpatient clinics at the American University of Beirut Medical Center between May and June 2004. Serum specimens were tested for anti-Toxocara antibodies by enzyme-linked immunosorbent assay and confirmed by Western blot. Multivariate analysis was performed to identify risk factors for infection. The seroprevalence rate of toxocariasis was 19%. Male gender and below high school education were significantly associated with a positive serological test (odds ratios = 3.1 and 2.8, respectively). Higher numbers of persons in the household, and low family income during childhood, were significant on bivariate analysis only. Toxocariasis is common in Lebanon. A large population-based survey is needed to confirm these results.

Ocular Toxocariasis in Schoolchildren

Ocular toxocariasis in humans is typically a unilateral disease caused by second-stage larvae of the Toxocara species. Serological evidence of widespread infection in humans provides little information on clinical disease. There is only a single previous estimate of the prevalence of ocular toxocariasis (from Alabama). The present survey examined the extent of consultant-diagnosed toxocaral eye disease among a population of schoolchildren. More than 120,000 participants were surveyed by questionnaire and follow-up. Two sets of control subjects from the same school and from the same county were compared with persons who had ocular toxocariasis. The prevalence of consultant-diagnosed toxocaral eye disease was 6.6 cases per 100,000 persons when only cases regarded as definite by the consultant ophthalmologist were included. This increased to 9.7 cases per 100,000 persons when both definite and strongly suspected cases were included. Geophagia and a history of convulsion were associated with toxocaral eye disease in both of the case-control studies.

Human toxocariasis: frequency of anti-Toxocara antibodies in children and adolescents from an outpatient clinic for lymphatic filariasis in Recife, Northeast Brazil

In a transversal study on a sample of 386 children and adolescents from an outpatient clinic for filariasis in Recife, Northeast Brazil, the frequency of anti-Toxocara antibodies and its relation to age, gender, number of peripheral eosinophils, Wuchereria bancrofti microfilariae and intestinal helminths was determined. The total anti-Toxocara IgG antibody frequency was 39.4%, by ELISA technique. The difference in frequency between males (40.1%) and females (37.6%) was not statistically significant. The 6 to 10-year-old subset presented the highest frequency of anti-Toxocara antibodies (60%), and within this age group there was a statistically significant male bias. There was also a significant association between the number of eosinophils and the presence of anti-Toxocara antibodies. Intestinal parasite frequency was 52.1%, but no association was found between this data and the presence of anti-Toxocara antibodies. In the present sample, 42.2% of the patients were Wuchereria bancrofti carriers, however, again this was not associated with the presence of anti-Toxocara antibodies. In conclusion, anti-Toxocara antibodies were highly prevalent in this sample. The present data show that there is no cross correlation between anti-Toxocara IgG antibody and the presence of intestinal helminths and filariasis.

A putative role for Toxocara species in the aetiology of multiple sclerosis

Multiple sclerosis (MS) is a disease of unknown aetiology. The finding of monoclonal antibodies in MS has been attributed to various infectious agents. Nematodes, such as Toxocara species have not been explored as possible aetiologic agents of MS. Some epidemiological studies have found an association between exposure to stress and household pets prior to the diagnosis of MS. In a case known to the authors, slight malaise and eosinophilia in peripheral blood preceded the diagnosis of MS by one year in a middle-aged man who lived in rural surroundings with cats in the household. The ubiquitary parasite Toxocara catis or canis is prevalent and serum antibodies are found regularly in populations examined. It is able to develop into the larval stage in human beings. The hypothesis presented here is that MS could be initiated by such infections in previously unexposed subjects under conditions of long-term stress.

Toxocariasis: clinical aspects, epidemiology, medical ecology, and molecular aspects

Toxocariasis is caused by a series of related nematode species (ascarids) that routinely infect dogs and cats throughout the world. The eggs from these ascarids are common environmental contaminants of human habitation, due largely to the fact that many kinds of dogs and cats serve as pets, while countless others run wild throughout the streets of most urban centers. The eggs, present in dog and cat feces, become infectious within weeks after they are deposited in the local environment (e.g., sandboxes, city parks, and public beaches, etc.). Humans, particularly children, frequently ingest these eggs by accident and become infected. Infection in humans, in contrast to their definitive hosts, remains occult, often resulting in disease caused by the migrating larval stages. Visceral larva migrans (VLM) and ocular larva migrans (OLM) are two clinical manifestations that result in definable syndromes and present as serious health problems wherever they occur. Diagnosis and treatment of VLM and OLM are difficult. These issues are summarized in this review, with emphasis on the ecology of transmission and control of spread to both humans and animals through public health initiatives employing treatment of pets and environmental intervention strategies that limit the areas that dogs and cats are allowed within the confines of urban centers.

Nephrotic syndrome associated with Toxocara canis infection

This case report describes nephrotic syndrome in a 7-year-old boy coincident with Toxocara canis infection. This rare association was confirmed by elevated Toxocara-specific IgM titres. Treatment with corticosteroids resulted in remission of renal symptoms as well as abatement of the T. canis infection. The relationship between T. canis infection and glomerular disease is still unclear; nephrotic syndrome may be another manifestation of T. canis infection.

Eosinophilia in the returning traveler

Eosinophilia is one of the most common laboratory abnormalities seen in the returning traveler. Although elevations in peripheral eosinophil levels can occur in a wide variety of disease processes, worldwide, helminth parasites are the major group of infectious agents responsible for eosinophilia. While often directed at helminth infections in their early stages of clinical evolution, the approach to the evaluation of the returning traveler with eosinophilia must consider the many causes of eosinophilia including those not casually related to travel. This article reviews the major parasitic causes of eosinophilia and provides a systematic approach to the evaluation of eosinophilia following travel.

Aspects of Toxocara epidemiology: human toxocarosis

Toxocarosis is the clinical disease in man caused by infection of zoonotic roundworms of dogs and cats, Toxocara canis and T. cati. In this review the mode of transmission to the human by oral ingestion of Toxocara eggs from the environment is discussed. T. cati seems to play a more important role than generally suggested. Direct contact with animals is not considered a potential risk because embryonation of excreted Toxocara ova requires a minimum of 2 weeks. For the same reason there is no relationship expected between infection and exposure to dogs and cats in the household. Children more frequently have clinical symptoms because of the closer contact with contaminated soil in yards and sandpits, the lack of hygiene, and because of eating dirt. Toxocara larval migration in the body can cause various clinical syndromes. Visceral larva migrans, ocular larva migrans, and covert toxocarosis are described. Serodiagnostic techniques are reliable tools to detect antibodies or antigens. Systemic treatment with anthelmintics is described but can result in hypersensitivity reactions caused by dying larvae. For ocular lesions, laser photocoagulation and corticosteroid therapy are described. Preventive measures consist of preventing contamination of the environment with Toxocara eggs and for education of pet owners and non-pet owners to increase awareness about potential zoonotic hazards. Veterinary practitioners, general practitioners, and public health agencies should therefore provide sufficient information and advice.

Prevalence of Toxocara spp. eggs in sandpits of parks in Osaka city, Japan, with notes on the prevention of egg contamination by fence construction

Toxocara spp. eggs were detected from 30 (75%) out of 40 sandpits of parks, in Osaka city. This prevalence was higher compared to those reported other areas of Japan. Since we examined a large quantity of sample, this could have resulted to higher prevalence. The number of eggs recovered decreased following fence construction around sandpits, but it did not sufficiently prevent the contamination of eggs. Improvement of fence design and education of sandpit users are necessary when contemplating fence construction around sandpits as a measure against contamination with Toxocara spp. eggs.

Toxocara canis infection in preschool age children: risk factors and the cognitive development of preschool children

Risk factors for Toxocara canis (T. canis) infection were evaluated in a prospective study of disadvantaged preschool children. In addition, the hypothesis that T. canis exposure is associated with lower intelligence was tested. Seropositivity was tested at 2 years, 3 years, and at 4 years 10 months (4-10). Intelligence was measured at age 4-10 by the Full Scale IQ of the Wechsler Preschool and Primary Scales of Intelligence (WPPSI). Pica and ownership of a dog were unrelated to seropositivity. Seropositive children had lower scores on the Mental Development Index (MDI) of the Bayley Scales of Infant Development at age 1 year (prior to likely exposure). They also had less favorable scores on a measure of the quality of childrearing. These findings suggest that, for disadvantaged children, lower initial intelligence and less advantageous child rearing are risk factors for T. canis exposure. Seropositive children also had higher blood lead levels, probably as a result of the common pathway of hand to mouth transmittal. Seropositivity at 3 years, at age 4-10, or, cumulatively, at any of the age 2, 3, or 4-10 assessments was associated with the WPPSI IQ after adjustment for sociodemographic factors. Exposure at age 4-10-years was significantly associated with reduced IQ scores (p = 0.030). However, when the age 1 year MDI score was controlled, the estimate became nonsignificant. We, thus, can neither confirm nor deny a relationship of T. canis and intelligence, but the importance of considering prior developmental status is emphasized.

Lymphedema as a presenting sign of toxocariasis

Toxocariasis in children is usually an asymptomatic infection and those with clinical illness have non-specific systemic or local manifestations. We present a 24-month-old boy with bilateral lymphedema of the feet as the main clinical manifestation of toxocariasis. The child presented with limping and nonpitting edema of both feet. Laboratory investigation revealed leucocytosis of < 20,000/mm3 with a differential count of < 50% eosinophils. No other cause of edema was found. The ELISA for toxocariasis revealed a high titer of > or = 1:4,096. The limping and the lymphedema disappeared during the third week of his illness. We suggest that toxocariasis should be considered as a possible cause of lymphedema and eosinophilia in young children.

Sero-epidemiology of toxocariasis in school children

The seroprevalence of toxocariasis was investigated in 2129 school children ranging in age from 4 to 19 years. Infection, as measured by titre, was found to be high compared to values obtained from children in other countries, with 31% having a titre of > or = 1:50 and 3.1% having titres of > or = 1:800. Relationships between seroprevalence and host factors including age, sex and location, and risk factors including geophagia, thumbsucking and pet ownership were explored. Age was found to be a significant factor in relation to infection with Toxocara. Males were significantly more infected than females, as were the inhabitants of rural schools versus urban schools. The percentage of seropositive children varied widely from school to school. Geophagia and pet ownership were found to be significantly associated with toxocariasis. Logistic regression analysis was used to model the relative contribution of these factors to infection with Toxocara. While this analysis identified factors which were highly significantly associated with Toxocara titre, the odds ratios were generally low indicating the low specificity of the model.

Parasitic infections of the central nervous system in children. Part II: Disseminated infections

In the second segment of this three-part review of parasitic infections of the central nervous system in children, we consider parasitic infections which typically involve various tissues and organs in addition to the brain and spinal cord. Parasites capable of dissemination in immunocompetent hosts are discussed first, and, as in Part I, organisms are grouped according to their predominant geographic location. This is followed by a discussion of the unique aspects of toxoplasmosis, strongyloidiasis and infection with microsporidia in immunocompromised patients, with an emphasis on the central nervous system.

Effect of various doses of infective Toxocara canis and Toxocara cati eggs on the humoral response and distribution of larvae in mice

The effect of 5-2,500 infective Toxocara canis and 5-1,000 T. cati eggs on the humoral immune response and on the distribution of larvae in the organism was studied in paratenic hosts--inbred C57BL6/J mice. With each dose of T. canis eggs the maximal antibody level was recorded on day 56 post infection and was followed by a moderate decline that lasted until day 154 of the experiment. A correlation between the antibody level and the egg count was observed only with the infective dose of 5-50 eggs. A more rapid occurrence of antibodies was recorded in mice infected with a high dose of eggs. In those given 5 and 7 T. cati eggs the antibody level exceeded the extinction threshold value only from day 21 to day 84. Low doses of T. canis (n = 5) and T. cati (n = 7) eggs caused a comparable distribution of larvae in mice, and the larval recoveries on day 70 post infection ranged between 10.00% and 25.74%. Following a dose of 500 T. cati eggs, 22.28% of the larvae were recovered, although only 1.08% were localized in the brain. A dose of 1,000 T. canis eggs yielded 36.37% of the larvae, with as much as 28.13% being found in the brain.

Comparable seropositivity for ascariasis and toxocariasis in tropical slum children

The seropositivities for infection by Ascaris lumbricoides and Toxocara canis were determined in children (1-15 years old) of a slum area of Caracas, Venezuela, and the levels that indicate the presence of active infection were defined. In children aged from 1 to 3 years, approximately 10% were positive for either parasite, and this figure increased to about 30% in 4- to 6-year-olds. For toxocariasis, the percentage of positivity remained at this level up to the age of 15 years. Whilst the positivity in children 10-15 years of age was comparable for Ascaris and Toxocara, a peak of positivity (50%) was found for Ascaris at 7-9 years of age. These results indicate that for these urban slum children, infection by Toxocara is essentially as common as that by Ascaris and, thus, that toxocariasis represents a potential public health problem in the tropical environment that is largely overlooked.

Diagnosis of human toxocariasis by antigen capture enzyme linked immunosorbent assay

AIMS

To evaluate an antigen capture enzyme linked immunosorbent assay (ELISA) which detects a carbohydrate epitope on the excretory-secretory (ES) antigens of Toxocara canis in clinical practice.

METHODS

Serum specimens from healthy adults, patients with acute visceral larva migrans, ocular and inactive toxocariasis, and with other helminth infections were examined by two site antigen capture ELISA.

RESULTS

Over half of the patients (19/28) with acute toxocariasis had a positive result in contrast to a small proportion of those with inactive disease (1/10) or ocular infection (2/7). False positive reactions, however, were found in 25% of the patients with serologically confirmed schistosomiasis and filariasis.

CONCLUSIONS

This assay is useful in confirming the diagnosis of acute visceral larva migrans but could not be used alone in diagnosis because of false positive reactions in patients with other helminth infections.

The prevalence of Toxocara canis ova in soil samples from parks and gardens in the London area

Toxocara canis is an ascarid parasite of the dog. Human infection is acquired when ova of T. canis are ingested. Parks and play areas contaminated with dog faeces are recognised as potential sources of infection. Five hundred and twenty one soil samples were examined from fifteen parks and gardens in the greater London area to establish the prevalence of soil contamination in those facilities. Samples were examined using a magnesium sulphate floatation method. T. canis ova were found in 6.3% of the samples. Positive samples were commonly found in lawns, playing fields and children's play areas. The authors believe that this may constitute a significant health risk, particularly to children.

Toxocara infection and epilepsy in children: a case-control study

A case-control study of 305 children was done to evaluate the relationship between toxocariasis and seizures and risk factors associated with toxocariasis transmission and seizure onset. A significant association existed between seropositivity for anti-Toxocara canis and seizures (p less than 0.05); the correlation was closest in children aged less than 5 years of age. Among risk factors, pica was more common in children with seizures than in controls but was not associated with toxocariasis. The association between dog ownership and toxocariasis was highly significant (p less than .000001). Our findings suggest that toxocariasis may be involved as a cofactor in the pathogenesis of seizures.

Surgical management of retinal traction caused by toxocariasis

We reviewed the results of vitreous surgery in 12 eyes of 12 patients with tractional macular detachment from Toxocara canis. We performed a vitrectomy and membrane peeling in all eyes, with additional scleral buckling in four eyes. After a minimum of six months' follow-up, ten of the 12 eyes (83%) had complete retinal reattachment. Visual acuity improved in seven eyes, two had no change, and three eyes had decreased visual acuity. Good postoperative vision correlated best with good preoperative vision. Preoperative traction retinal folds through the macula were associated with a poor visual outcome.

A serological survey of toxocariasis in patients and healthy donors in Barcelona (Spain)

The ELISA test, using excretory-secretory antigen from larvae II of Toxocara canis, was applied on 1018 sera (793 from adults and 225 from pediatrics) distributed in: A) patients with an hypereosinophilia where the ethiological agent was undetermined (99); B) patients with ocular complaints compatible with an ocular toxocariasis (116); C) patients with hidatidosis (97); D) patient with other non-toxocaral helminthiasis (34); E) patients with other clinical features (468) and F) healthy donors (204). Over 3,6% of sera showed elevated levels of antibodies reacting with T. canis antigen. The prevalence of seropositivity was statistically higher in patients with eosinophilia (14,1%) (a less than 0,001) and ocular complaints (6%) (0,025 greater than alpha greater than 0,01) than in the control group (1%). In the overall seropositivity from pediatrics did not differ from that of the adults.

The epidemiology of Toxocara canis

Bred as hunter, companion and pet, the dog has a long and honourable association with man. Yet the domestic dog can host a wide range of parasites - many of which can also infect humans. One of these, the ascarid nematode Toxocara canis (Fig. 1), is of particular interest because of retinal damage that may result from larvae becoming trapped in the eye. At the Hospital for Tropical Diseases in London, about 20-30 patients with toxocariasis are treated annually. Widespread fouling of public parks, playgrounds and pedestrian areas with dog faeces - especially in large cities - is well -recognized as one of the main sources of Toxocara infection. Yet as Stephen Gillespie discusses here, epidemiological indicators vary widely and the risk of infection is often treated too lightly.

The expanded spectrum of toxocaral disease

Among 137 members of 30 families, 6% (and 8% of those aged under 15 years) were seropositive for toxocara antibodies. In these seropositive subjects and in 84 patients known to have raised toxocara titres the commonest clinical features were abdominal pain, hepatomegaly, anorexia, nausea, vomiting, lethargy, sleep and behaviour disturbances, pneumonia, cough, wheeze, pharyngitis, cervical adenitis, headache, limb pains, and fever. 61% of patients with raised toxocara titres had recurrent abdominal pain. Eosinophilia was in many cases associated with a raised toxocara titre, but 27% of patients with high titres had normal eosinophil counts. Toxocariasis is common, especially in children, and is associated with clinical features that are generally regarded as non-specific but together form a recognisable symptom complex. Toxocariasis should be considered in the differential diagnosis of such symptoms and especially in recurrent abdominal pain, which might otherwise be labelled as idiopathic. The absence of eosinophilia does not exclude toxocariasis.