Purified protein derivative of Mycobacterium tuberculosis and excretory-secretory antigen(s) of Toxocara canis expand in vitro human T cells with stable and opposite (type 1 T helper or type 2 T helper) profile of cytokine production

A large series of T cell clones (TCC) specific for purified protein derivative (PPD) of Mycobacterium tuberculosis (total 60) or Toxocara canis excretory/secretory (TES) antigen (total 69) were established from the peripheral blood of two healthy individuals and analyzed for their profile of cytokine production in response to stimulation with either the specific antigen or the polyclonal activator phorbol myristate acetate plus anti-CD3 antibody. Under both these experimental conditions, the great majority of PPD-specific TCC secreted IL-2 and IFN-gamma but not, or limited amounts of, IL-4 and IL-5. In contrast, most TES-specific TCC secreted IL-4 and IL-5 but not, or limited amounts of, IL-2 and IFN-gamma. PPD-specific TCC that failed to secrete IL-4 and IL-5, and TES-specific TCC that failed to secrete IL-2 and IFN-gamma, were found to lack transcripts for IL-4 and IL-5, or for IL-2 and IFN-gamma, respectively. During the course of the study, over a 6-mo period, the functional phenotype of both TES- and PPD-specific TCC was repeatedly assessed and remained constant. These data demonstrate that T cells with stable Th1 or Th2 functional pattern exist not only in mice but also in humans and suggest that in the course of natural immunization certain infectious agents preferentially expand T cell subsets with stable and definite profile of cytokine production.

Highlights of human toxocariasis

Human toxocariasis is a helminthozoonosis due to the migration of Toxocara species larvae through human organism. Humans become infected by ingesting either embryonated eggs from soil (geophagia, pica), dirty hands or raw vegetables, or larvae from undercooked giblets. The diagnosis relies upon sensitive immunological methods (ELISA or western-blot) which use Toxocara excretory-secretory antigens. Seroprevalence is high in developed countries, especially in rural areas, and also in some tropical islands. The clinical spectrum of the disease comprises four syndromes, namely visceral larva migrans, ocular larva migrans, and the more recently recognized "common" (in adults) and "covert" (in children) pictures. Therapy of ocular toxocariasis is primarily based upon corticosteroids use, when visceral larva migrans and few cases of common or covert toxocariasis can be treated by anthelmintics whose the most efficient appeared to be diethylcarbamazine. When diagnosed, all of these syndromes require thorough prevention of recontamination (especially by deworming pets) and sanitary education.

Toxocariasis: serological diagnosis by enzyme immunoassay

An enzyme-immunoassay was developed to measure the concentration of serum antibody specific for the secretory antigens released by migrating toxocaral larvae. This technique was evaluated by testing sera from healthy UK adults, and from patients with and without toxocariasis. In 922 healthy adults, 2.6% were found to have elevated specific antibody levels. Elevated values were observed twice as frequently in males as in females but showed no significant regression with age between 20 and 65 years. Of 62 patients with non-toxocaral helminthic infections, all had antitoxocaral antibody levels within the range of values observed in healthy controls and had a mean level which was not significantly elevated. All of 13 patients with clinical toxocariasis had enzyme-linked immunosorbent assay (ELISA) antibody levels above the 100th percentiles of both the healthy population and the helminth-infected group and had a significantly high mean value (p less than 0.001) more than 12 times that of the healthy or infected controls. The high degree of sensitivity and specificity of the toxocariasis enzyme-immunoassay indicates that this new test should be useful in reference immunodiagnostic applications and in large-scale seroepidemiological surveys.

How common is human toxocariasis? Towards standardizing our knowledge

Our understanding of the global impact and cost of human toxocariasis is poor because there is insufficient clinical awareness and no clear repository for the efficacy of clinical, laboratory and treatment interventions. Uniform clinical and laboratory investigative approaches maximize disease diagnosis. International collaboration is required to develop web-based, professional educational support, surveillance questionnaires and standardized serodiagnostic criteria. Determining clinical benefits and treatment outcomes using less crossreactive antigens will enhance clinical and treatment interventions. Increased liaison will identify realistic occurrence and prevalence data and cost benefits of intervention. Web-based centres of excellence and repositories of current knowledge, which augment current veterinary and public health educational sites, should be supported. Expected outcomes should be capable of addressing the clinical and financial burdens of this treatable disease.

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.

Application of the western blotting procedure for the immunodiagnosis of human toxocariasis

To improve the immunodiagnosis of human toxocaral disease, a sensitive and specific assay using the Western blotting procedure (WB) with excretory-secretory antigens from Toxocara canis larvae (TES) was developed and compared with the standard enzyme-linked immunosorbent assay method (TES-ELISA) using the same antigens. We tested groups of sera from laboratory animals or patients presenting with toxocariasis or other helminthic diseases and a group of sera from people dwelling in an area endemic for toxocariasis who exhibited hypereosinophilia. Statistically, the WB assay correlated well with TES-ELISA, but the former was more specific for banding patterns corresponding to low-molecular-weight fractions, thus avoiding problems of cross-reactivity with sera infected with other helminthic diseases.

Characterization of surface and excretory-secretory antigens of Toxocara canis infective larvae

The surface antigens of Toxocara canis infective larvae have been identified by radio-iodination and compared with the excretory-secretory (ES) products released by the larvae in vitro. Common antigens, of molecular weight 32 000 and 120 000 are found on the larval surface, in the ES material and in culture supernatant following surface iodination of living T. canis larvae. The 120 000 antigens consist of three closely migrating bands in each of these preparations. However, one prominent ES component, of molecular weight 400 000, is not found on the larval surface. Additional molecules of 55 000 and 70 000 are present in the ES material, but while these may be discerned in surface preparations there appears to be more heterogeneity of surface molecules in this size range. Both sets of molecules are antigens to infected patients and experimental animals. A comparison of characterized human sera show that a radio-immunoprecipitation assay correlates with the established ELISA test (r = 0.89), and that all labelled molecules are antigenic to the infected host.

Immunodiagnosis of toxocarosis in humans: evaluation of a new enzyme-linked immunosorbent assay kit

Excretory/secretory (E/S) antigen derived from second-stage larvae of Toxocara canis maintained in defined medium in vitro has been well established worldwide for the immunodiagnosis of human toxocarosis by enzyme-linked immunosorbent assay. Such an enzyme-linked immunosorbent assay, based on the detection of human anti-T. canis (E/S antigen) serum immunoglobulin G, has recently been commercialized by Biokema-Affinity Products (Crissier-Lausanne, Switzerland). This commercial test kit was evaluated with regard to its application in a routine diagnostic laboratory and the reliability of the results. Of 78 patients with suspected clinical toxocarosis, 71 had anti-T. canis antibodies (positive serological result) corresponding to a diagnostic sensitivity of 91%; 14% of serum samples (n = 199) from patients with protozoan or with helminthic infections also showed positive reactions mainly related to infections with Trichinella, Strongyloides, and Fasciola species. An epidemiological study with 1,000 serum samples from randomly selected healthy blood donors and children in Switzerland demonstrated a seroprevalence of 2.7%. The test kit under evaluation had an overall diagnostic sensitivity of 91% and a relative specificity of 86%, the latter being related to some protozoan and helminthic infections. Because of the scarcity of such infections, potential cross-reactivity does not play a major role under the conditions found in the middle part of Europe. In conclusion, the application of the test kit provided for use in this study can be recommended for routine diagnostic use.

Seroprevalence estimates for toxocariasis in people worldwide: A systematic review and meta-analysis

Background

Human toxocariasis is an important neglected disease. We performed a systematic review and meta-analysis study to estimate the global and regional prevalence of anti-Toxocara serum antibodies (referred to as ‘T-seroprevalence’) in human populations around the world.

Methods

We searched five international databases (PubMed, EMBASE, Web of Science, SciELO and Scopus) for seroprevalence studies published from 1 January 1980 to 15 March 2019. We used random effect models to calculate the overall T-seroprevalence (with 95% CIs) in all six WHO regions and worldwide. We also conducted subgroup and linear meta-regression analyses to evaluate the impact of socio-demographic, geographical and climatic parameters on seroprevalence.

Results

We identified 250 eligible studies (253 datasets) comprising 265,327 participants in 71 countries for inclusion in the present meta-analysis. The estimated global T-seroprevalence rate was 19.0% (95%CI, 16.6–21.4%; 62,927/265,327); seroprevalence was highest in the African region (37.7%; 25.7–50.6%) and lowest in the Eastern Mediterranean region (8.2%; 5.1–12.0%). The pooled seroprevalence for other WHO regions was 34.1% (20.2–49.4%) in the South-East Asia; 24.2% (16.0–33.5%) in the Western Pacific; 22.8% (19.7–26.0%) in the American; and 10.5% (8.5–12.8%) in the European regions. A significantly higher T-seroprevalence was associated with a lower income level; lower human development index (HDI); lower latitude; higher humidity; higher temperature; and higher precipitation (P-value < 0.001). Potential risk factors associated with seropositivity to Toxocara included male gender; living in a rural area; young age; close contact with dogs, cats or soil; consumption of raw meat; and the drinking of untreated water.

Conclusions

The present findings indicate high levels of infection with, or exposure to Toxocara spp. in many countries, which calls for increased attention to human toxocariasis and improved measures to prevent adverse health risks of this disease.

There have been many epidemiological studies on the seroprevalence of Toxocara infection or toxocariasis in humans in individual countries, but there has been no systematic review/meta-analysis to estimate the extent of Toxocara infection or exposure in human populations worldwide. By reviewing 250 studies of 265,327 people from 71 countries, we provide the first comprehensive global estimates of T-seroprevalence in humans to date. The findings indicate that almost one fifth (19%) of the world’s human population is seropositive to Toxocara. The highest seroprevalence rates were found in Africa (37.7%) and the lowest in the Eastern Mediterranean region (8.2%). Individual countries with high HDIs and high income levels usually had low T-seroprevalence rates. Our findings also showed that T-seroprevalence varies markedly among countries, according to geographical location (coordinates) and climatic features. Evidence from this study indicates that human toxocariasis is a prevalent, neglected tropical disease and potentially one of major importance to global public health. Our study emphasizes the need for governmental authorities to pay increased attention to the risks and socioeconomic impact of HT in many countries around the world, and for them to design and implement HT prevention or control programs, considering risk predictors identified here.

Relationship between allergic manifestations and Toxocara seropositivity: a cross-sectional study among elementary school children

Toxocara (the cause of visceral larva migrans in humans) and allergy have in common both elevated immunoglobulin E (IgE) levels and eosinophilia. In the present study, we investigated: 1) associations between Toxocara seropositivity and allergic manifestations; 2) risk factors for Toxocara infection; and 3) differences in Toxocara seroprevalence, allergic manifestations and the associations between these two, in children from urban and rural environments. Blood samples from 1,379 Dutch urban and rural elementary schoolchildren, were examined for Toxocara antibodies, eosinophil numbers, total IgE concentrations, and the occurrence of inhaled allergen-specific IgE. Questionnaires investigating respiratory health and putative risk factors for infection were completed. It was found that 8% of the children had Toxocara antibodies, occurring significantly less often in females than in males. The means of total serum IgE levels and blood eosinophils were significantly higher in the Toxocara-seropositive than in the seronegative group. Allergic asthma/recurrent bronchitis was found in 7% of the children, allergic reaction on animal contact in 4%, and IgE to at least one inhaled allergen in 16%. These variables were associated with Toxocara seroprevalence. Inhaled allergen-specific IgE and asthma/recurrent bronchitis occurred significantly less often in rural than in urban areas, and significantly less often among girls than among boys. Furthermore, occurrence of allergen-specific IgE increased significantly with age. No association existed between Toxocara seroprevalence and assumed risks, i.e. contact with pet animals and public playgrounds. In conclusion, our results indicate that allergic manifestations occur more often in Toxocara-seropositive children. A relationship with an already existing allergic condition is plausible.

Larva-specific antibodies in patients with visceral larva migrans

Seven of 10 patients with visceral larva migrans (VLM) had serum precipitating antibodies specific for larval antigens of Toxocara canis as determined by double diffusion in agar. Such antibodies were absent in 114 normal adults and 25 patients with collagen disease. Precipitation of ascarid components by C-reactive protein resulted in false-positive reactions, but this precipitation was readily prevented by appropriate absorption of sera before testing. A more sensitive assay, the enzyme-linked immunosorbent assay, revealed high titers of antibodies to larvae of Toxocara in all patients with VLM; the log2 titer ranged from 9 to 14. Five of eight household relatives of these patients and four children who had had VLM two to four years before testing had titers of 6-12. Of the 114 normal adults, 105 had titers of 0-2; nine had titers of 3-8. Of the 25 patients with collagen disease, 23 had titers of 0, and two had titers of 4 and 6, respectively. Additional studies of those patients indicated that infection with Toxocara can be distinguished serologically from ascariasis, filariasis, and trichinellosis.

A serological follow-up of toxocariasis patients after chemotherapy based on the detection of IgG, IgA, and IgE antibodies by enzyme-linked immunosorbent assay

A serological follow-up study was carried out on 27 children (1-12 years old) with visceral and/or ocular toxocariasis, after treatment with thiabendazole. A total of 159 serum samples were collected in a period ranging from 22-116 months. Enzyme-linked immunosorbent assays (IgG, IgA, and IgE ELISA) were standardized, using excretory-secretory antigens obtained from the second-stage larvae of a Toxocara canis culture. The sensitivity found for the IgG, IgA, and IgE ELISA, as determined in visceral toxocariasis patients, was 100%, 47.8%, and 78.3%, respectively. Approximately 84% of the patients presented single or multiple parasitosis, as diagnosed by stool examination, yet such variables did not appear to affect the anti-Toxocara immune response. Titers of specific IgE antibody showed a significant decrease during the first year after treatment, followed by a decrease in the IgA titers in the second year, and in the IgG titers from the fourth year onwards. Sera from all patients presented high avidity IgG antibodies, indicating that they were in the chronic phase of the disease. Moreover, 1 year after treatment, the level of leukocytes, eosinophils, and anti-A isohemagglutinin in patients decreased significantly. The present data suggest that IgE antibodies plus eosinophil counts are helpful parameters for patient follow-up after chemotherapy.

Environmental exposure to Toxocara as a possible risk factor for asthma: a clinic-based case-control study

The zoonotic ascarid Toxocara has been suggested as a possible etiologic agent of asthma. We conducted a clinic-based case-control study to examine whether the zoonotic infection acquired by ingesting Toxocara eggs is associated with asthma in children. Blood samples were collected from children aged 2-15 years, 95 of whom had asthma and 229 of whom did not have asthma. Risk factors for asthma and Toxocara infection were assessed by a questionnaire given to each child's parent or legal guardian. Blood samples were tested for the presence of Toxocara antibodies, using an enzyme-linked immunosorbent assay. No significant association was found between Toxocara infection and asthma. Significant associations were found between asthma and risk factors and between Toxocara infection and risk factors. High prevalence of Toxocara infection was noted among Hispanic children of Puerto Rican descent.

Circulating excretory-secretory antigen levels and specific antibody responses in mice infected with Toxocara canis

Circulatory excretory-secretory antigen levels and IgM and IgG responses to larval antigens were monitored in the serum of 20 BALB/c mice that had been given approximately 500 infective eggs of Toxocara canis by stomach tube. Other groups of mice received different doses of infective eggs, ranging from 5 to 1,250 eggs. Excretory-secretory antigens were collected from culture fluid in which mechanically hatched larvae of T. canis were maintained. An indirect enzyme-linked immunosorbent assay was used to monitor specific antibody responses. Circulating antigen levels were monitored using a direct ELISA which incorporated an IgG fraction of a rabbit antiserum to the excretory-secretory antigens as a capture antibody and a biotin-conjugated form of the same rabbit IgG as the second antibody. The antigen-specific IgM response was evident the first week of infection and peaked 3 to 6 weeks post-infection. The antigen-specific IgG response first appeared the second week of infection and peaked at 6 to 8 weeks post-infection. Both isotype levels stayed near their peak values for the remainder of the study. In the untreated sera, circulating antigen was initially evident and highest the first week of infection; the antigen concentrations dropped by the third month of infection to low, but significant, levels that persisted for the duration of the study. The administration of greater than 25 eggs produced antigenemias. There appeared to be a positive linear trend between the number of eggs given and the amount of antigen in the circulation.

The effect of temperature and antimetabolites on antibody binding to the outer surface of second stage Toxocara canis larvae

In vitro maintained second stage Toxocara canis larvae do not bind antiserum raised to their excretions and secretions (ES) at 37 degrees C as detected by indirect fluorescence. However, when these larvae were incubated at 2 degrees C under the same conditions intense fluorescence on the whole outer surface was observed. This fluorescence remained as long as the larvae were maintained at 2 degrees C. When these larvae were reincubated at 37 degrees C a gradual loss of fluorescence along their outer surfaces occurred. This loss was complete after 3 h. Larvae which were preincubated in antimetabolites at 37 degrees C exhibited intense fluorescence on their outer surfaces as did those incubated at 2 degrees C with antimetabolites. It is concluded that antigens present in ES occur along the whole length of the larval outer surface and turn over at 37 degrees C. This turnover occurs along the whole outer surface and is metabolically dependent. Should this occur in vivo it could afford the parasite with a mechanism for evasion of the immune response.

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

To determine epidemiological and clinical associations with Toxocara canis seropositivity, we studied 333 (87%) children of a cohort of 383 five- to seven-year-olds. The prevalence of seropositivity (antibody titer to T canis, greater than or equal to 1:32) was 23.1%. Black children were more frequently seropositive than were white children, as were children of parents who did not graduate from high school. In a sample of seropositive and seronegative children, seropositivity was associated with both a history of pica and puppy ownership, but not with a greater frequency of symptoms and signs that occur in visceral larva migrans or with poor growth. No child had evidence of ocular toxocariasis on retinal examination. For the whole sample, poor reading achievement, marked distractibility, and lower intelligence were associated with seropositivity, but by using multiple regression analysis, we found that these associations may be attributable to confounding variables.

Toxocara seroprevalence in 5-year-old elementary schoolchildren: relation with allergic asthma

Toxocara seroprevalence and the relation between Toxocara seroprevalence and allergic asthma were investigated in Dutch schoolchildren aged 4-6 years. Data on Toxocara antibodies, allergen-specific immunoglobulin E, allergic manifestations, and risk factors (pets and playgrounds) were obtained from 235 children from The Hague and 477 from Rotterdam, the Netherlands. The surveys were carried out from September 1987 to January 1988 in The Hague and in March and April 1989 in Rotterdam. Logistic regression was used to evaluate putative relations. Toxocara seroprevalence was higher in The Hague (11%) than in Rotterdam (6%), but this difference was not quite significant. Seroprevalences varied widely among schools. No differences between socioeconomic categories or between the sexes were found. Occurrences of asthma/recurrent bronchitis and hospitalization due to asthma/recurrent bronchitis were significantly associated with seroprevalence. Furthermore, a marginally significant relation with eczema was found. Immunoglobulin E specific for inhaled allergens occurred significantly more often in the Toxocara-seropositive group. The risk factors investigated were not related to seroprevalence. It is suggested that Toxocara, among other environmental factors, may stimulate polyclonally immunoglobulin E production, including allergen-specific immunoglobulin E, and thus may contribute to the manifestation of allergic asthma and possibly of eczema in children predisposed to allergy.

Seroprevalence of zoonotic toxocariasis in the United States: 1971-1973

Demographic characteristics associated with human Toxocara canis infection in children aged one to 11 years were investigated using data from the Health and Nutrition Examination Survey of 1971 to 1973. An enzyme-linked immunosorbent assay with larval stage antigen was used to measure the concentration of antibodies to T. canis in 1,409 available sera. From 4.6 to 7.3% of the children in different geographic regions of the United States have been infected, with serologic prevalence approaching 30% among black children of lower socioeconomic status aged six to 11 years. For both blacks and whites, higher seroprevalence was associated with a rural residence, increased age in children and number of persons in the household, and with decreased income, education, and number of rooms in the house. Multivariate logistic regression models indicated that blacks had higher infection rates than whites, even when socioeconomic factors were controlled. Certain critical variables, however, such as exposure to dogs or reliable pica histories, were not available for analysis.

Thiabendazole vs. albendazole in treatment of toxocariasis: a clinical trial

Between 1986 and 1988, 34 patients (age range six to 83 years) with visceral or ocular larva migrans were randomly assigned to a five-day treatment with thiabendazole 2 x 25 mg kg-1 day-1 (15 patients) or albendazole 2 x 5 mg kg-1 day-1 (19 patients). On the fifth treatment day, six patients (40%) in the thiabendazole group and 11 patients (58%) in the albendazole group showed excellent or good drug tolerability. Efficacy of treatment was assessed after 30 weeks (range six to 56 weeks). In the thiabendazole group, median eosinophilia remained at 14% and four patients (27%) were clinically cured. In the albendazole group, the median eosinophilia decreased from 10 to 3.5% and six patients (32%) were clinically cured. We recommend albendazole for treatment of visceral and ocular larva migrans with a minimum dose of 10 mg kg-1 daily for five days.

ELISA for diagnosis of ocular toxocariasis

The enzyme-linked immunosorbed assay test was positive in 37 of 41 patients (90%) suspected of having clinical Toxocara infections. The antigen used in this test is prepared from the Toxocara egg and is felt to be extremely specific in making the diagnosis. The prevalence of Toxocara infection is much greater than previously believed. It is hoped that this test will help the surgeon fell more secure in not enucleating eyes containing masses suggestive of Toxocara infection.

The secreted and somatic antigens of the third stage larva of Anisakis simplex, and antigenic relationship with Ascaris suum, Ascaris lumbricoides, and Toxocara canis

The in vitro-released 'excretory/secretory' (ES) and somatic antigens of the third stage (infective) larva of Anisakis simplex were characterised by radioiodination, immunoprecipitation, and sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Oral infection with the parasite elicited a substantial IgG antibody response to ES in infected rabbits and humans, with a minimal response to somatic materials. Serial serum sampling in experimental infection showed that there was a sequential recognition of distinct ES components. In contrast to oral infection, intraperitoneal exposure of rats with living parasites induced a strong response to both ES and somatic antigen preparations. Sequential recognition of ES antigens, and differential responses to somatic components, might, therefore, have application in the estimation of the age and degree of penetration by the nematodes in human infection. Extensive antigenic relationships were found between A. simplex and three other species of ascaridoid nematodes, namely Ascaris lumbricoides, Ascaris suum, and Toxocara canis, but none with a panel of non-ascaridoid nematodes. Evidence is presented that a Mr 14,000 component of A. simplex has a homologue in all of the ascaridoids examined, but does not elicit an antibody response in anisakiasis. Finally, the ES of A. simplex is shown to contain two proteinase activities, of approximately Mr 23,400 and 46,100, as revealed by separation on gelatin substrate gels, although the antigenicity of the enzymes remains to be established.

Eosinophilic granuloma of the liver: a characteristic lesion with relationship to visceral larva migrans

Children with the clinical syndrome of visceral larva migrans as a result of Toxocara species have typical lesions in the liver and other viscera, consisting of palisading granulomas that contain numerous eosinophils and often Charcot-Leyden crystals; recognizable parasites are uncommon. Similar eosinophilic granulomas that are found incidentally in adults often cause diagnostic problems. To define better the clinical, laboratory, and pathologic features of these lesions, we reviewed 43 cases of hepatic eosinophilic granuloma (excluding cases of Langerhans' cell histiocytosis) collected in the files of the AFIP over a period of 31 years. The eosinophilic granulomas were found in patients of all ages (range 12 months to 77 years); 30% were younger than 20 years. There were 26 male and 17 female patients. Most patients (26 of 43; 60%) were asymptomatic, and the lesions were discovered incidentally. Others had fever (20%) or abdominal pain (20%). The granulomas were typically multiple (61%), with central necrosis surrounded by a mixed inflammatory infiltrate with numerous eosinophils and variable numbers of neutrophils. lymphocytes, and a palisade of epithelioid histiocytes and/or giant cells. Charcot-Leyden crystals were present in 19 cases (44%). Remnants of parasites (eight Toxocara sp., two Capillaria sp.) were identified in the tissue in 10 patients. There was a positive serologic test for Toxocara sp. in five additional cases. Immunohistochemical staining using polyclonal antiserum against Toxocara canis larvae demonstrated positivity in macrophages in eight of 13 cases tested. We conclude that identification of an eosinophilic granuloma in the liver should suggest the diagnosis of visceral larva migrans and prompt a search for the causative organism with serial sectioning of the block and serologic tests for Toxocara and other causative parasites.

Specificity of Toxocara ELISA in tropical populations

The diagnosis of human infection by Toxocara canis relies heavily upon serological tests, the specificity of which can be inadequate in regions of endemic helminthiasis. When different population groups of tropical Venezuela were evaluated using ELISA based upon Toxocara excretory-secretory antigen (TcESA), solid-phase adsorption of the sera with extracts of a wide variety of non-homologous parasites revealed the existence of significant cross-reactivity. This was effectively and conveniently overcome when the test sera were incubated in the presence of the soluble parasite extracts in a competitive inhibition ELISA. The mean reduction of ELISA values caused by pre-adsorption of the sera tested was 32.2%, and that caused by competitive inhibition was 42.3%, the effects of these two procedures being strongly correlated (r = 0.83). The magnitude of the reduction was inversely proportional to the actual ELISA value (r = -0.55), and ranged from a mean of 68.0% in sera from apparently healthy individuals of medium-high socio-economic level, down to 28.1% in heavily parasitized Amazon indians. Ascaris showed the greatest degree of cross-reactivity in these tests, although under conditions of competitive inhibition even sera with high levels of antibody against this parasite could be negative in Toxocara ELISA. Western blotting revealed a major 81,400 D component that was shared between Ascaris and TcESA. Our results indicate that the competitive inhibition of cross-reactivity by soluble non-homologous parasite extracts provides a convenient and economical means of increasing the specificity of ELISA for the determination of the seroprevalence of toxocariasis in tropical populations.

Toxocara seroprevalence in children from a subtropical city in Argentina

Most studies from Argentina have focused on toxocariasis as an environmental problem of big cities, and there are no available data about children infection from small or middle-sized cities. In order to assess the prevalence of anti-Toxocara antibodies in infantile population, 206 children from Resistencia, of both sexes, aged 1-14 years old were studied by Elisa testing with E/S T. canis L2 antigens. Hematological parameters and immunoglobulin levels were determined; five days' stool samples were studied and epidemiological data were obtained by means of a questionnaire to parents. Results showed that 73% of the children had one or more dogs living at home, 57% reported geophagia and 37.9% were positive for Toxocara serology, but there was no significant difference in prevalence neither for boys and girls, nor concerning age. An increased risk of infection was observed in age groups 5-6 and 7-8 for boys, and in age groups 3-4 and 5-6 for girls.