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When maintained in culture, the infective-stage larvae of Toxocara canis produce a group of excretory-secretory antigens. Monoclonal antibodies to these antigens have been produced and partially characterized. Hybridomas were made using spleens from mice that had been given 250 embryonated eggs of T. canis followed by immunization with excretory-secretory antigens. Monoclonal antibodies were first screened against excretory-secretory antigens using an indirect enzyme-linked immunosorbent assay. Those antibodies positive in this assay were then screened against the surfaces of formalin-fixed, infective-stage larvae using an indirect fluorescent antibody assay. The two monoclonal antibodies showing fluorescence were also tested against the surfaces of infective-stage larvae of Toxocara cati, Baylisascaris procyonis, Toxascaris leonina, Ascaris suum, a Porrocaecum sp., and Dirofilaria immitis. One of these two antibodies bound to the surface of T. canis and T. cati while the other bound only to the surface of T. canis; neither were reactive with the other ascaridoid larvae or the larvae of D. immitis. Enzyme-linked immunoelectrotransfer blotting techniques were used to demonstrate that the cross-reactive antibody recognized antigens with molecular weights of about 200 kDa while the more specific monoclonal antibody recognized antigens with approximate molecular weights of 80 kDa. The specificity of these two antibodies for T. canis and T. cati should prove helpful in the development of more specific assays for the diagnosis of visceral and ocular larva migrans.

By means of indirect immunofluorescent antibody reaction (IFAR), using serum of experimentally infected pigs, various antigens were studied with regard to their usefulness for serological verification of prepatent Ascaris suum and Toxocara canis infections. Eggs, egg larvae, larvae received from livers, lungs and brains of experimentally infected white mice and sections of adult T. canis as well as eggs, egg larvae, liver larvae and sections of frozen adult A. suum proved to be not suitable for the reliable serum diagnosis of the infections. On the other hand, A. suum larvae, isolated from lungs of white mice or guinea pigs days after experimental infection, represent an antigen applicable to IFAR for the evidence of prepatent A. suum infections in pigs. The antigen, stored at -20 degree C, is durable without substantial impairment of its reactivity at least 7 months.

Three, six-month-old dogs were infected with 2,000 eggs of Toxocara canis. Three weeks after infection 15 immature adult parasites were found in the intestine of the dog which had been treated with high doses of corticosteroids (2 ml of Opticortenol S given every four days) while no parasites were found in the intestine of the dog treated with repeated injections of 0.3 ml Opticortenol S or in the untreated control dog. The increased susceptibility to infection with T. canis in the dog treated with high doses of corticosteroids was associated with a decrease in in vitro lymphocyte responsiveness to the mitogen concanavalin A and pokeweed mitogen and with a complete suppression of the eosinophilia that was seen 10 days after infection in the untreated control dog.

This study describes the presence of circulating toxocaral antigens (CTA) in the sera of dogs infected with Toxocara canis (T. canis) by using a sandwich enzyme-immunoassay (SEIA). A specificity of this assay with different antigens was observed, i.e. the EIA values, which express the antigen concentration, of excretory-secretory antigen from T. canis larvae were higher than those of other antigens (Ascaris lumbricoides, Dirofilaria immitis and Fasciola hepatica). The variability in intra-assay was below 10%. In age distribution of CTA levels, the highest level was observed at 1 month of age. Thereafter, the levels decreased gradually until 6 months of age and then the same levels were maintained until adult age. Also, slightly elevated levels were found in the sera of foetuses. A significant correlation was obtained between age and CTA levels. The positive correlation between the number of worms and CTA levels was significant. As for the IgG, IgM and IgA antibodies, a significant correlation was observed between the IgM antibody activities and CTA levels, but this was not observed with IgG and IgA antibodies. From these results, it was indicated that the immunological response to T. canis infection in dogs may not be reached until 1 or 2 months after birth, although detectable CTA levels were observed in foetal and early life. It was also suggested that the immunological stimulation for canine toxocariasis may be maintained by the excretory-secretory materials from the larvae through life and as a result, IgM antibody production may be observed even in chronically infected adult dogs. The SEIA technique reported in this study may be useful as a diagnostic tool of human toxocariasis, since the CTA can be directly demonstrated by the technique.

The data generated by quantitative enzyme-immunoassay of antibody activity are unsuitable for direct communication from the laboratory to clinician. In this paper, the fundamental problems of reporting ELISA results are highlighted and a list of desirable characteristics is set out for such reports. The available methods for processing ELISA data are reviewed in relation to these ideal requirements and the deficiencies and advantages of each method are discussed. The performance of each method is demonstrated by the use of actual test data from a model ELISA system. No single method has been found which satisfies all criteria.

Strain-, sex- and age-based resistance of mice to Toxocara canis infection was demonstrated. Infection doses of similar numbers resulted in significantly (P less than 0.05) greater worm establishment in CD1 mice than in NIH mice, as well as a greater heterogeneity of responses between individuals. Male mice had significantly (P less than 0.05) fewer larvae in the brain and more larvae in the liver than female mice, when mice of greater than or equal to 3 months old were used. Appreciably more larvae were retained in the liver of male CD1 mice than in NIH mice. Orchidectomized mice had higher levels of brain infestation and a lower larval recovery from the liver compared with intact male mice. Infections in young mice of both strains showed more diversity in establishment and migration pattern between individuals than in older mice. Despite these differences in distribution of larvae and in the numbers recovered from experimental infections, the acute and chronic clinical signs observed in the two strains were very similar.

Peripheral blood eosinophilia, histology of skeletal muscle and brain, and larval recovery were compared between congenitally athymic nude mice (nu/nu) and thymus-bearing heterozygous littermates (nu/+) for 6 weeks following oral infection with Toxocara canis eggs. By comparing patterns of peripheral blood eosinophil levels in nu/+ and nu/nu, two types of eosinophilias, one T cell dependent and the other independent, were observed. Eosinophil infiltration and granuloma formation around larvae in the skeletal muscle were weaker in degree in nu/nu than nu/+. The total number of larvae in nu/+ decreased from 2 to 6 weeks after infection. This decrease was directly related to a decrease in larval number in skeletal muscle, not in brain or other tissues. In contrast, no significant decrease of the total number of larvae was observed in nu/nu. The results indicate that eosinophilia, granuloma formation and larval recovery are closely related to cell-mediated immune mechanisms in T. canis-infected mice.

Sera were examined from an age-stratified sample of two Caribbean communities using the Toxocara-ELISA with larval ES antigen. Seropositivity was markedly age dependent, attaining maximal values (40 and 60%) in 5-15 year olds and declining in adults. The rate of acquisition of infection with Toxocara canis and the age-prevalence profile are similar to those of Ascaris lumbricoides and Trichuris trichiura. It is suggested that toxocariasis is likely to be prevalent in tropical areas with endemic geohelminthiasis.

Investigations were made by means of a larvae precipitation test (LPT) on different laboratory animals (pigs and white mice, and pigs, rabbits, guinea pigs and white mice respectively) experimentally infected with Ascaris suum and Toxocara canis respectively for the serological evidence of specific A. suum and T. canis antibodies. Living A. suum larvae isolated from the lungs of experimentally infected white mice forming oral, excretion porus and cuticula precipitates proved to be a suitable antigen for the intravital evidence of prepatent A. suum infections in pigs and mice. By using living T. canis larvae from lungs, liver and brain of infected mice as antigen prepatent T. canis infections in pigs, rabbits, guinea pigs and mice were serologically proved because of precipitates on oral and excretion porus. It was found for the first time that frozen preserved larvae of A. suum and T. canis are suitable for the evidence of specific antibodies and--because of the faster and more exact determination of the results as well as the possible preserving of the antigen--superior to the test on living larvae.

A primate model for the study of Toxocara canis infection was created by intravitreal, periocular, systemic, and intracarotid injection of viable larvae in cynomolgus monkeys. The results were as follows: (1) Intravitreal larvae caused retinal hemorrhages, perivasculitis, mild vitritis, and retinal nodules. (2) Apparently viable larvae without inflammatory reaction were found in the vitreous, retina, and optic nerves up to nine months after intravitreal inoculation. (3) Other larvae were surrounded by an acute inflammatory granuloma or a chronic fibrotic granuloma, but they did not appear to be necrotic. (4) Toxocara canis larvae apparently had the ability to move through ocular tissue, to leave the site of tissue reaction, and to exit via the optic nerve. Viable larvae were found in the retina up to 15 months after inoculation. (5) Culture fluid containing Toxocara proteins stimulated a severe retinal vasculitis. Dead larvae caused little reaction. (6) Positive aqueous and vitreous enzyme-linked immunosorbent assay titers were found in the most severely inflamed eyes, which often harbored live larvae.

Peripheral lymphocytes from macaques inoculated with Toxocara canis and from children with serologically confirmed visceral larva migrans (VLM) were assayed for blastogenic responses using Toxocara antigen and standard mitogens. Macaques were given single or multiple larval infections. Lymphocyte responses of inoculated macaques were compared with responses from noninoculated macaques. Similarly, lymphocyte responses from 2 serologically confirmed human Toxocara VLM patients were compared with that of 2 healthy human controls. Mitogen responses of the macaques with multiple infections were higher than those with single infections or no infection, but these differences were not significant. Statistically greater (P less than 0.05) Toxocara antigen-induced blastogenesis was observed for both groups of inoculated macaques and for each VLM patient. However, the degree of stimulation was low.

An in vitro larval precipitate test using second-stage Toxocara canis larvae and an indirect fluorescent antibody (IFA) test employing cuticles of T. canis larvae as antigen were evaluated using antisera produced in pigs experimentally infected with T. canis, T. cati, Ascaris suum, Toxascaris leonina and Parascaris equorum. The former test was both specific and sensitive and is suggested as a reliable and simple method of detecting Toxocara antibodies in pigs. The latter test was considered unsuitable because of cross-reactions that occurred when sera from pigs infected with other ascarids were tested. An IFA test for Ascaris antibodies, employing cuticles of A. suum larvae as antigen, is described. The degree of specificity of this test suggests that it may be of value in the detection of antibodies to Ascaris in pigs under natural conditions.

Two cases of presumed ocular toxocariasis are reported in 19-year-old college students. One presented with an acute exudative intraocular inflammation, with marked peripheral eosinophilia, while the other had only minimal inflammatory changes of the disc and vitreous. Both had elevated Toxocara antibody titers by the enzyme-linked immunosorbent assay (ELISA) method. The simultaneous occurrence of ocular toxocariasis in friends and the early presentation and detection of their ocular lesions make these 2 cases interesting. The presence of positive laboratory data with only minimal clinical disease in one of the cases suggests that ocular toxocariasis may be more common than is usually appreciated.

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.

The distribution of excretory-secretory antigens of larval Toxocara canis (TEX) in tissue was studied in cases of both acute and chronic experimental murine toxocariasis. Liver samples were collected from BALB/c BYJ mice killed either 2 days (acute) or 8 months (chronic) after intragastric inoculation with infective T. canis eggs. Cryostat sections of liver were stained using biotin-conjugated, rabbit anti-TEX antibody with an avidin-fluorescein isothiocyanate indicator. In both acute and chronic infections larval sections were brightly fluorescent. The patterns of antigen deposition in acute infections were indicative of larval migration. In tissue sections from chronic infections, antigens were observed mainly within the core of granulomas centered around larvae and within the inner rim of the collagen capsule of granulomas in which a larva or larval remnant was not detected. When present within the collagenous capsule, TEX appeared to be extracellular. These findings suggest that an accurate histopathological diagnosis of larval toxocariasis may be possible in biopsy or autopsy material lacking an obvious etiological agent.

Test mice have been selectively reared for high (H) or low (L) immune responses to Nematospiroides dubius. After secondary infection with N. dubius, the L mice voided ten times as many eggs in their faeces as the H mice, and at necropsy, 71% versus 20% of the inoculum of N. dubius were recovered as adult worms from the L and H mice respectively. Furthermore, N. dubius were more fecund in the L than in H mice. High or low immune responsiveness was not restricted to N. dubius infection in these mice but was also observed during Toxocara canis infection. The migration of T. canis larvae from gut via the liver to skeletal muscle and CNS was inhibited in H versus L mice. Many more larvae were recovered from the livers of H compared with L mice which was indicative of greater immunity in the H mice. The protective immune response in H compared with L mice to both N. dubius and T. canis included pronounced eosinophilia and elevated antiparasite antibody titres.

Chemotactic reactivity of eosinophils obtained from the bone marrow (BM-Eo) of cyclophosphamide-treated, Toxocara canis-infected mice was compared to that of eosinophils obtained from the peritoneal cavity (PEC-Eo). BM-Eo responded well to alanyl-tetrapeptide, a synthetic eosinophil chemotactic factor of anaphylaxis (ECF-A), whereas PEC-Eo did not. Both BM-Eo and PEC-Eo showed almost equally high chemotactic reactivity to parasite-derived ECF, ECF lymphokine and complement-derived ECF. Chemotactic reactivity of BM-Eo to synthetic ECF-A was deactivated by preincubation with ECF-A. Unresponsiveness of PEC-Eo to synthetic ECF-A could be explained by chemotactic deactivation by ECF-A, because an ECF-A-like substance was detected in the ascitic fluid; this substance could deactivate the chemotactic reactivity of BM-Eo to synthetic ECF-A. From these results, BM-Eo are naive and seem to be a good indicator for eosinophilotaxis and its modulation.

In this study, the relationship between the IgA antibody activities to Toxocara canis infection in dogs and their parasitologic status has been examined. The enzyme-linked immunosorbent assay was applied to the sera of dogs for the detection of the specific IgA antibodies and at the same time, autopsy and stool examination were performed on these dogs. The most elevated IgA antibody levels were observed in the one-month age group of puppies. Thereafter, the levels gradually decreased until six and 10 months of age. These low levels were maintained in adult dogs. However, the IgA antibody activities were not related to the age and the number of worms when the correlation coefficients were calculated. It was suggested from the results obtained that the elevated IgA antibodies at one month of age may have been due to the locally stimulated immunity by the adult worms grown up in the intestines and as a result, could be detected in the circulation.

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.

In the sera of dog fetuses and newborn puppies, no antibody to Toxocara canis was found but an elevation of the circulating toxocaral antigens (CTA). In the mother dogs, detectable IgG and IgM antibodies were found. The IgG antibodies gradually increased in the course of this observation. The most elevated levels of IgA antibodies were observed one month after birth. The same was true for the CTA levels. There was no placental transfer of the antibodies nor could they be transferred from the mother dog to the offspring via the colostrum.

The visceral infection of humans with Toxocara canis is particularly prevalent in children and may cause a variety of symptoms that commonly persist for 6-24 months. The ocular infection usually causes permanent loss of visual acuity. Human infection is acquired by ingestion of embryonated T. canis eggs with contaminated dirt. Review of recent reports indicates that patent T. canis infection is widely prevalent in the general population of dogs all over the world (3-81%) and results in a substantial contamination of the ground (0.3-87%). The results of sensitive and specific serological tests suggest that about 7% of the clinically healthy human population of the United States, about 5% of that of Canada, and about 4% of that in Great Britain is infected with the parasite. Control of transmission of the parasite to man is often attempted by eliminating the infection in dogs, reducing the population of dogs and the environmental contamination with their feces, and educating the public about the zoonotic potential of toxocariasis. The evidence reviewed indicates that these methods are only marginally effective. Because T. canis relies on congenital and lactogenic transmission to persist in nature, only a procedure that effects the sustained killing of the reservoir larvae in the tissues of the bitch, or of newly-acquired parasites, is expected to be successful. Research with mice, rabbits and dogs demonstrated that prior infections of the host induce the development of protective immunity to reinfections. This procedure, however, leaves remnant populations of larvae from the immunizing infections that are resistant to anthelmintics and to the effect of prior irradiation. Hyperimmunization with partially-purified extracts of T. canis larvae induced 37% resistance to a challenge in mice when the extract was administered alone, and 76% resistance when administered with lipopolysaccharide adjuvant. Production of complete resistance, however, will probably require the prior control of the immunosuppression induced by the parasite. T. canis infections inhibit the production of homologous protective immunity and antibody responses to heterologous antigens, probably by interfering with the activity of helper T-cells, competing with protective antigens, and suppressing antibody synthesis. The evidence indicates, however, that an anti-T. canis vaccine to eliminate the parasite in dogs is feasible.

Infection of CBA/J mice with 250 ova of Toxocara canis results in development of splenic lymphocytes hyperergic to nonspecific stimuli. These studies were performed to see if the granulomatous response to a nonspecific stimulus was exaggerated. Using eosinophil counts and MBSA ear thickening it was demonstrated that concurrent infection with the parasite and immunization with methylated bovine serum albumin (MBSA) elicit no immunologic cross reactions. Eosinophil counts were proportional to the worm burden and unaffected by concurrent MBSA immunization. Embolization of Sepharose 4B beads conjugated to MBSA into the pulmonary vasculature of MBSA-immune mice, elicited large, florid macrophage-rich granulomata while in MBSA-naive mice infected with 10 T. canis ova, the beads elicited small, foreign body reactions. In MBSA-naive mice infected with 250 T. canis ova MBSA-coated beads elicited eosinophil-rich granulomata that were as large or larger than the granulomata in MBSA-immune mice. In mice immune and infected, lesions contained eosinophils in proportion to larval worm burdens. Because MBSA beads elicited large, eosinophilic granulomata in T. canis infected, MBSA-naive mice it is concluded that the lung is hyperergic and the disease process appears similar to other kinds of eosinophilic pneumonitis such as bronchial asthma or Loeffler's pneumonia.

The aqueous humor and serum samples of patients with presumed ocular toxocariasis were examined by an enzyme-linked immunosorbent assay (ELISA) for antibody to the embryonated egg antigen. Using a single dilution (1:8), higher amounts of antibody have been found in the aqueous humor than in the serum samples. Antibody was not found in the serum or aqueous humor of patients with retinoblastoma, Coats' disease, uveal malignant melanoma, or central retinal artery obstruction. While two patients with presumed ocular toxocariasis had normal serum levels of antibody, the aqueous humor ELISA titers were greatly elevated, supporting the clinical diagnosis and suggesting localized antibody production.

In order to interpret the relation between the IgM antibody activities to Toxocara canis (T. canis) and the parasitologic status, sera from puppies and adult dogs were measured by the enzyme-linked immunosorbent assay. At the same time, autopsy was performed on these dogs for counting the number of T. canis worms and stool examination was carried out for observing the fertilization of eggs. The rates of infection by T. canis in the dogs decreased with age. The number of worms in the intestines ranged one to 39. The IgM antibody activities gradually increased until 3 months of age. Thereafter the significant levels were maintained even at the adult age. However, the IgM antibody levels were not associated with the age and the number of worms (P greater than 0.05) when the correlation coefficients were calculated between them. In contrast to the IgG antibodies, the results of the present study indicated that the IgM antibody activities do not relate to the age, the number of worms and the fertilization of eggs.

Serological surveys, measuring humoral antibody responses, have indicated significant levels of human infection with the zoonotic nematode Toxocara canis, and raised concern about the resultant risk of ocular and neurological damage. Such measurements do not distinguish with certainty current infection from past exposure. Thus, we have developed a test for circulating Toxocara antigen released by parasites in the host. This monoclonal antibody-based two-site 'sandwich' assay discriminates between T. canis and the related feline ascarid T. cati, and has been used, in tandem with the standard ELISA, to examine experimental and human infections. In experimental animals, antigen is transiently detectable, disappearing when immunocomplexed with host antibody. Antigen was also found in sera from UK patients diagnosed with visceral or ocular toxocariasis, and in four asymptomatic Papua New Guinean children. In the latter population, individuals positive for parasite antigens were not necessarily positive for antibody, implying that some infected cases may be negative in the current diagnostic ELISA. The antibody test was also adapted to measure host antibody directed to single monoclonal antibody-defined epitopes, revealing evidence of differential temporal regulation of distinct antibody specificities.

The levels of immunoglobulin E (IgE) in aqueous humor (AH) and serum were determined in 74 uveitis patients and 13 control patients with senile cataract. Uveitis patients' levels ranged from less than 0.06 to 460 IU/ml according to the paper radioimmunosorbent test (PRIST; limit of sensitivity, 0.06 IU/ml). Only one control patient had an AH level higher than the sensitivity limit (0.08 IU/ml). Of the five patients with the highest levels in the AH, four had toxocaral retinitis. The ratio of AH/serum to IgE normalized to the albumin concentration was calculated in 25 uveitis patients and was greater than 0.60 in 13 cases, indicating a possible intraocular IgE synthesis.

Splenic responses of CBA/J mice infected with 250 embryonated ova of the nematode, Toxocara canis were characterized during the first month post-inoculation (P.I.). By the 6th day of infection, spleen to body weight ratios were over 3.5 times greater in infected mice than uninfected controls. This ratio peaked at 5.0 on day 14 and declined slightly by day 36 P.I. Lymphocyte transformation studies were carried out using the T cell mitogens, Con A and PHA and the B mitogen, LPS. The responses of infected mice to all of the mitogens were greater than or equal to the responses of uninfected mice at all times studied. Unstimulated lymphocytes from infected mice spontaneously incorporated approximately 10-fold more 3H-TdR than did uninfected control mice during the first 2 weeks of infection. Antigen-specific lymphocyte transformation was also performed using a crude extract of homogenized embryonated ova (TEE) as the antigen. Positive responses were obtained at all times examined but were greatest during the first 2 weeks of infection. The T cell basis of this response was demonstrated by Anti-Thy 1.2 plus complement treatment prior to the initiation of the lymphocyte transformation assay. Collectively, these results suggest that in mice, T. canis elicits a striking splenomegaly as early as 1 week after oral inoculation. The lymphocyte transformation studies suggest that the splenomegaly may be due in large part to proliferation of the white pulp based on the amount of spontaneous labelling observed. Increased mitogenic responses indicate that T. canis does not elicit nonspecific immunosuppression and the positive response to the TEE antigen suggests that at least some of the lymphoproliferation is antigen specific.

A standardized microtest plate enzyme-linked immunosorbent assay (ELISA) was developed using the microsomal fraction of adult worms of Schistosoma mansoni (MAMA) as antigen. A standard reference serum pool was prepared and arbitrarily designated as having 100 activity units per microliter. The precision of the test, the suitability as a standard of the reference serum pool, and the J index as a method of determining the significant level of reactivity were evaluated. The predictability of the assay for patients with S. mansoni infections and for non-schistosomiasis patients was 95%. Preliminary studies with the truly quantitative microtest plate kinetic ELISA indicate that this assay is suitable for standardization for schistosomiasis and toxoplasmosis. The need for WHO International Reference Sera with designated International Units and for well-defined batteries of sera for evaluating the specificity and sensitivity of assays was emphasized.

In the regions of Basel, Jura and Zürich (Switzerland) 765 blood donors completed a questionnaire with respect to symptoms, animal contacts and occupation, and their sera were tested for antibodies to tissue helminths in ELISA. 5.1%, 3.3% and 6.5% exhibited antibodies solely to the respective antigens of Toxocara canis, Fasciola hepatica, and Echinococcus granulosus. Combined seroreactions were mainly observed between F. hepatica and E. granulosus antigens. Reactivity to T. canis antigen was associated with animal contacts at work, as well as contacts with cattle and sheep but not dogs or cats. Toxocara antibodies were found in all age groups. Their prevalence varied markedly by region.

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 immunological responsiveness of CBA/J mice infected with various numbers of the canine ascarid, Toxocara canis, was characterized after a single infection to ascertain the smallest infection capable of perturbing the immune system of the host. Mice receiving the lowest inoculations (5 eggs per mouse or 0.25 larvae per g of body weight) had detectable alterations in the number of circulating peripheral blood eosinophils and spleen weight-to-body weight ratios. Mice infected with 25 eggs each (1.25 larvae per g of body weight) showed augmented concanavalin A-elicited splenic lymphocyte transformation and a positive lymphocyte transformation in response to a toxocaral antigen preparation in addition to even higher eosinophil counts and heavier spleens. Spleen cells from mice receiving the two largest inocula (125 eggs and 250 eggs per mouse or 6.25 and 12.5 larvae per g of body weight, respectively) had in addition to the above responses a sixfold increase in spontaneous DNA synthesis. An enzyme-linked immunosorbent assay for mouse antibody responses to T. canis indicated that the time of onset as well as the magnitude of the antitoxocaral humoral response is directly proportional to the size of the inoculation used to initiate the infection. Finally, we showed that allowing the infection to become protracted results in some responses increasing somewhat in magnitude, but regardless of length of infection, the magnitude of any of the responses examined is proportional to the size of the infection. The results indicate that different host responses have different thresholds of sensitization and suggest that larvacidal reactions which require intricate interactions among several components of the immune system may not occur in very small infections.

The indirect fluorescent antibody test using frozen sections of infective Toxocara canis and Toxascaris leonina eggs, and the enzyme linked immunosorbent assay using homogenized Toxocara canis embryonated egg extract and T canis excretory-secretory products as adsorbed antigens were used to determine the specificity and development of circulating antibodies in rabbits. Frozen sections were subdivided into four morphologically distinct compartments for analysis of the development of the circulating antibody response. The fluid surrounding the larva was the most reactive up to 21 days after infection, and this material was found to be predominantly excretory-secretory in nature. As the infection progressed antibodies directed against 'somatic' tissue materials increased. Cross reactions between sera from rabbits infected with T. canis eggs and Toxascaris leonina frozen sections, and rabbits infected with T. leonina eggs and Toxocara canis frozen sections occurred between both the excretory-secretory fluid and somatic components of the infective eggs. These results were substantiated using the enzyme linked immunosorbent assay. When T. canis excretory-secretory antigen was used, an earlier response (peak day 21) was detected than when using T. canis embryonated egg extract (peak day 35). However, cross reactions between T. canis excretory-secretory antigen and sera from rabbits infected with Toxascaris leonina occurred, indicating that the serodiagnosis of visceral larva migrans using Toxocara canis excretory-secretory antigen may still prove unsatisfactory when considering the role of Toxascaris as a possible causative agent.

An experimental model for studying anaphylactic histamine release from rat peritoneal cells in vitro is described. Rats were sensitized by feeding the infective eggs of ttoxocara canis, the antigen being prepared from the infective eggs. The characteristics of histamine release are comparable with those found for other anaphylactic systems. Addition of 0.2% inactivated normal rat serum to the incubation media reduced the spontaneous histamine release from 11.5 +/- 1.9% to 3.1 +/- 1.6% (mean +/- SD) of total histamine, whereas the corresponding figure for anaphylactic histamine release was 41.3 +/- 19.7%. Both disodium cromoglycate (DSCG) and levamisole produced a dose-related inhibition of histamine release, with DSCG being the more potent drug.

Intravitreal infection of guinea pigs with second-stage larvae of Toxocara canis and second- and fourth-stage larvae of Ascaris suum induced intraocular IgE antibodies and a dense eosinophil infiltration in the anterior chamber and throughout the uveal tract. The eosinophil infiltrate began within 1 day after infection and persisted for as long as 51 days. By day 12 after intravitreal infection, the injected ascarid larvae were surrounded by granulomas which consisted almost entirely of eosinophils. Firm adherence of eosinophils to the parasite cuticle, morphologic alterations and degranulation of eosinophils with the deposition of free eosinophil granules on the parasite surfaces, and ingestion of eosinophils and eosinophil granules by the parasite larvae also were observed. Intravitreal injectionof a soluble antigen derived from third-stage A. suum molting to the fourth-stage in defined media in vitro also induced intraocular IgE antibody and a diffuse ocular eosinophil infiltrate. Dense eosinophil infiltration of the choroid, not immediately adjacent to a parasite larva, was accompanied by destruction of the lverlying outer retina, with cystic changes in the retina and between the retina and the choroid. Few eosinophils were observed within the retina, and the retinal destruction may be the result of direct toxic action of constituents of the choroidal eosinophils. Evidence which indicates that the eosinophil is the principal effector cell in immunity to helminth infections and is cytotoxic for the parasites, possible mechanisms for the induction of the ocular eosinophil infiltrates, and evidence for autotoxicity by eosinophils are briefly reviewed, and the potential roles of the eosinophil in the ocular response to helminth parasites are discussed.

The sera from 660 healthy blood donors from Canberra were tested for antibodies to Toxocara canis by the ELISA test. The results were compared with those from patients with suspected or confirmed visceral larva migrans or ocular toxocariasis. Over 7% of Canberra sera showed elevated levels of antibody reacting with T. canis antigen. Sera from patients resident in Australia with other helminth parasites did not cross-react with T. canis antigen in our tests. However, studies of sera collected in several tropical countries with other parasitic infection, show that cross-reactions with other parasites are possible. The use of purified glycoprotein antigen does not alter the possibility of cross-reaction. Observations and experiments show that people in Canberra may be exposed to the infective eggs of T. canis.

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.

In order to elucidate the relationship between eosinophilia and IgE antibody production in parasitic infection, the degree of eosinophilia and IgE antibody levels to larval ES antigen of Toxocara canis were investigated in eight inbred strains of mice after infection with T. canis. Eosinophilia was far higher in degree in SJL mice than in the other inbred strains. However, IgE antibody levels to larval ES antigen in SJL mice were the lowest among those inbred strains. Similarly, the degree of eosinophilia in AKR mice was slightly higher than those in the other strains except SJL mice, but IgE antibody levels to larval ES antigen in AKR mice was as low as that in SJL mice. Consequently, high responders for eosinophilia were not always high responders for IgE antibody production to larval ES antigen. Inheritance of the two traits, marked eosinophilia and poor IgE antibody production to larval ES antigen in T. canis infected SJL mice, were investigated using F1 hybrid and back-cross mice. The former was regulated by more than one gene, while the latter was a recessive trait. The degree of eosinophilia after infection showed no relationship with the total numbers of larvae recovered from T. canis infected inbred mice.

In this study, we have developed a reliable radioimmunoassay (RIA) for Ascaris suum protein (Asp) and have measured the serum concentration of Asp in control subjects and in patients with helminthiasis and a variety of gastrointestinal diseases. The cross-reactivities of Asp antibody with other helminth worm antigens were also measured by RIA. Ascaris lumbricoides contained approximately the same amount of Asp antigenic substance as did Ascaris suum. Toxocara canis had a high concentration of a substance partially cross-reactive with Asp. Small amounts of substance cross-reacting with Asp were also exhibited by Anisakis larvae, Schistosoma japonicum and Taenia saginata. However, no cross-reactivities of Fasciola hepatica and Paragonimus westermani with Asp were observed in this study. Almost all the serum levels of Asp from normal control subjects were below the sensitivity of this RIA (10 ng/ml). High concentrations of Asp were observed in sera from patients with ascariasis (64.5 +/- 18.8 ng/ml: mean +/- S.E.), anisakiasis (75.2 +/- 28.0 ng/ml), toxocariasis (78.4 +/- 31.3 ng/ml) and schistosomiasis japonica (14.3 +/- 3.4 ng/ml). Asp levels in sera from patients with other helminthiasis were not significantly high. From these findings, it was suggested that RIA for Asp may not be specific for diagnosis of ascariasis, but might be a suitable screening method for patients with some kinds of helminthiasis. Interestingly, high concentrations of Asp were also observed in sera from patients with ulcerative colitis (24.8 +/- 2.5 ng/ml) and Crohn's disease (19.8 +/- 5.2 ng/ml), but Asp levels from 7 other gastrointestinal diseases seemed not to be significantly high. These findings remain unexplained but may derive from cross-reactivities between helminthic and gut mucosal antigens.