Clinically inapparent Toxocara infection in children

Toxocariasis-Associated Acute Perimyocarditis with Cardiogenic Shock: A Case Report

Patient: Female, 21-year-old

Final Diagnosis: Toxocariasis-associated acute perimyocarditis with cardiogenic shock

Symptoms: Dizziness • epigastric pain • headache • vomiting

Medication: —

Clinical Procedure: —

Specialty: Cardiology

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.

Toxocariasis-associated cardiac diseases--A systematic review of the literature

Toxocariasis, caused by Toxocara canis or Toxocara catis, is a worldwide occurring parasitic disease, reaching high prevalences especially in tropical and subtropical countries. The clinical presentation can range from asymptomatic seropositivity to life threatenting disease, depending on the organ system involved. Cardiac involvement, one of the possible manifestations of human Toxocara spp. infection, is rarely reported in case reports. As far as we know, no systematic reviews of clinical presentations have been published till now and no clear recommendations regarding the treatment of Toxocara spp. infection involving the heart exist. In a systematic review of the literature, 24 published cases of Toxocara spp. infection involving the heart were identified. The cardiac entities described included myocarditis, pericarditis, and Loeffler's endocarditis. The clinical presentation ranged from asymptomatic or mild disease to life threatening myocarditis/pericarditis with heart failure or cardiac tamponade, leading to death. In most cases, the diagnosis was based on a combination of clinical, laboratory and radiological findings. Only in three of the nine cases in which histological analysis was performed (either pre- or post-mortem), granulomas or remnants of the parasite were detected. In the other six cases, findings were non-specific; the damage of the heart was equally caused by direct invasion of the larvae and by immunological reactions, either caused by the systemic hypereosinophilia or by the presence of the larvae in the tissue. The treatment regimen described mostly consisted of anthelmintic drugs in combination with corticosteroids. Even though dosage and duration of treatment varied widely, ranging from days to months, most patients were treated successfully. Cardiac involvement in Toxocara spp. infection is a rare but potentially life-threatening complication of a very common disease. The therapeutic regimens vary widely especially with regard to the duration of therapy, however, the combination of an anthelmintic drug and a corticosteroid appears to be a valuable option. For the daily clinical work, tissue manifestation by parasites should be considered in cases of unspecific organ manifestations, (i.e. heart, lungs, liver), accompanied by fever and eosinophilia with or without allergic skin rashes.

Toxocariasis diagnosed in international travelers at the Institute of Tropical Medicine, Antwerp, Belgium, from 2000 to 2013

Although infection with Toxocara canis or T. catis (commonly referred as toxocariasis) appears to be highly prevalent in (sub)tropical countries, information on its frequency and presentation in returning travelers and migrants is scarce. In this study, we reviewed all cases of asymptomatic and symptomatic toxocariasis diagnosed during post-travel consultations at the reference travel clinic of the Institute of Tropical Medicine, Antwerp, Belgium. Toxocariasis was considered as highly probable if serum Toxocara-antibodies were detected in combination with symptoms of visceral larva migrans if present, elevated eosinophil count in blood or other relevant fluid and reasonable exclusion of alternative diagnosis, or definitive in case of documented seroconversion. From 2000 to 2013, 190 travelers showed Toxocara-antibodies, of a total of 3436 for whom the test was requested (5.5%). Toxocariasis was diagnosed in 28 cases (23 symptomatic and 5 asymptomatic) including 21 highly probable and 7 definitive. All but one patients were adults. Africa and Asia were the place of acquisition for 10 and 9 cases, respectively. Twelve patients (43%) were short-term travelers (< 1 month). Symptoms, when present, developed during travel or within 8 weeks maximum after return, and included abdominal complaints (11/23 symptomatic patients, 48%), respiratory symptoms and skin abnormalities (10 each, 43%) and fever (9, 39%), often in combination. Two patients were diagnosed with transverse myelitis. At presentation, the median blood eosinophil count was 1720/μL [range: 510-14160] in the 21 symptomatic cases without neurological complication and 2080/μL [range: 1100-2970] in the 5 asymptomatic individuals. All patients recovered either spontaneously or with an anti-helminthic treatment (mostly a 5-day course of albendazole), except both neurological cases who kept sequelae despite repeated treatments and prolonged corticotherapy. Toxocariasis has to be considered in travelers returning from a (sub)tropical stay with varying clinical manifestations or eosinophilia. Prognosis appears favorable with adequate treatment except in case of neurological involvement.

Analysis of the course and treatment of toxocariasis in children-a long-term observation

Toxocariasis is a helminthozoonotic disease caused by ascarid larvae of Toxocara genus: Toxocara canis and Toxocara cati. In the reported study, the clinical course of toxocariasis and administered therapy were evaluated in 103 children. The majority of the children (68.9%) were from the rural environment, with a prevalence of boys (62.1%). At diagnosis of infection, 36 (35%) children reported recurrent abdominal pain, 19 (18.4%) headache, 6 (5.8%) loss of appetite, 2 subfebrile conditions, and 2 arthralgia, Moreover, 23 (22.3%) children demonstrated symptoms of atopic diseases; in 30 (29.1%) children, moderate enlargement of lymphatic nodes was noted. In five children (4.9%), ophthalmic examination revealed unilateral changes in the eye: in two cases retinitis; in one case fibrotic lesions in the vitreous body, complicated 1 year from diagnosis by retinal detachment; and in other children parafoveal lesions and cataract. Only two children with ocular changes at diagnosis reported visual disorders. In 64.3% of children, eosinophilia was observed. A covert form of the disease was diagnosed in 95.1% of the children and an ocular form in 4.9%. In all the children, antiparasitic treatment was implemented, repeated several times in some of them. After therapy, the mean titer of specific antibodies, the number of children with abdominal pains and enlarged lymphatic nodes were decreased, while headaches maintained at unchanged levels. In approximately one fourth of the children with negative results of antibodies after the therapy, the symptoms of the disease were still reported. Evaluation of the efficacy of treatment is not easy due to non-characteristic symptoms and low kinetics of specific anti Toxocara IgG decrease; however, high IgG titers suggest non-effective treatment of concomitant infection requiring subsequent therapy. Due to risk of ocular form, which may develop in any stage of the disease, irrespectively of specific antibodies concentrations, it seems justified to implement antiparasitic treatment in all children infected with T. canis.

Seroprevalence of Toxocara infection in children and environmental contamination of urban areas in Paraná State, Brazil

The objectives of this study were to evaluate the contamination by eggs of Toxocara in sandy areas or grass lawns of outdoor recreation areas that are used by children, and the frequency of seroprevalence in children, from three cities of fewer than 45,000 inhabitants in Paraná, Brazil. From May 2005 to December 2007, five samples were taken from each of 13 sandy sites and 18 grass lawns, all from plazas and public schools. Blood samples from children aged 0-12 years were analysed by immunoassay for anti-Toxocara IgG. The soil samples were processed by floatation and sedimentation. Eggs of Toxocara spp. were present in 44.7% (38/85) of the samples from grassed areas and in 21.4% (15/70) of the sand samples. The lawns were 2.16 times more contaminated than the sand (P = 0.0009). However, the epidemiological variables showed no statistically significant difference between seropositive (36.8%; 130/353), and seronegative children. The rate of seropositivity was higher in children aged 0-5 years (P = 0.03), who were 1.94 times more likely to develop persistent wheezing (P = 0.02).

An alternate technique for isolation of Toxocara canis excretory-secretory antigens

The aim of the present study was to test the effectiveness of a sausage-casing membrane for dialysis of Toxocara excretory-secretory antigens (TES). The protein concentrated by the tested membrane was compared with that obtained using a Sigma commercial membrane, as were the protein fractions found by polyacrylamide gel electrophoresis. Standard positive and negative serum samples were evaluated in an ELISA immunoassay, and equivalent data were obtained in all steps, indicating that the sausage-casing membrane is efficient, besides being less expensive to process.

A simplified method for hatching and isolating Toxocara canis larvae to facilitate excretory-secretory antigen collection in vitro

Human toxocariasis causes several dangerous syndromes that can involve the viscera, vision and central nervous system. Diagnosing toxocariasis requires the identification of antibodies against Toxocara canis or Toxocara cati excretions and secretions (ES). To obtain ES it is necessary to collect a large number of larvae. However, since the earliest work describing the culture of Toxocara larvae, few advances in the method have been made. It has been suggested that carbon dioxide triggers molecular mechanisms that enable nematode hatching. A similar hypothesis has been made regarding Giardia excystation. To test the hypothesis we used the Giardia excystation HBSS method to hatch embryonated T. canis eggs. We found that the HBSS method was more effective than the original De Savigny method. Our results suggest that both parasites require stimulation in an acidic environment, and the abrupt change to a basic milieu in duodenum. This physiological adaptation is successful to exploit the intestinal habitat.

Serological, clinical and epidemiological evaluation of toxocariasis in urban areas of south Brazil

Toxocariasis is a worldwide public-health problem that poses major risks to children who may accidentally ingest embryonated eggs of Toxocara. The objectives of this study were to investigate the occurrence of anti-Toxocara spp. antibodies in children and adolescents and the variables that may be involved, as well as environmental contamination by Toxocara spp. eggs, in urban recreation areas of north central mesoregion, Paraná State, Brazil. From June 2005 to March 2007. a total of 376 blood samples were collected by the Public Health Service from children and adolescents one to 12 years old, of both genders. Samples were analyzed by the indirect ELISA method for detection of anti-Toxocara antibodies. Serum samples were previously absorbed with Ascaris suum antigens, and considered positive with a reagent reactivity index >1. Soil samples from all of the public squares and schools located in the four evaluated municipalities that had sand surfaces (n = 19) or lawns (n = 15) were analyzed. Of the 376 serum samples, 194 (51.6%) were positive. The seroprevalence rate was substantially higher among children aging one to five years (p = 0.001) and six to eight years (p = 0.022). The clinical signs and symptoms investigated did not show a statistical difference between seropositive and seronegative individuals (p > 0.05). In 76.5% of the investigated recreation places, eggs of Toxocara were detected in at least one of the five collected samples. Recreation areas from public schools were 2.8 times more contaminated than from public squares. It is important to institute educational programs to inform families and educators, as well as to improve sanitary control of animals and cleaning of the areas intended for recreation in order to prevent toxocariasis.

Human toxocariasis: contribution by Brazilian researchers

In the present paper the main aspects of the natural history of human infection by Toxocara larvae that occasionally result in the occurrence of visceral and/or ocular larva migrans syndrome were reviewed. The contribution by Brazilian researchers was emphasized, especially the staff of the Tropical Medicine Institute of São Paulo (IMT).

Ocular lesions in gerbils (Meriones unguiculatus) infected with low larval burden of Toxocara canis: observations using indirect binocular ophthalmoscopy

To study the frequency of ocular lesions in 30 gerbils infected with 100 embryonated eggs of Toxocara canis, indirect binocular ophthalmoscopy was performed 3, 10, 17, 24, 31 and 38 days after infection. All the animals presented larvae in the tissues and 80% presented ocular lesions. Hemorrhagic foci in the choroid and retina were present in 92% of the animals with ocular lesions. Retinal exudative lesions, vitreous lesions, vasculitis and retinal detachment were less frequent. Mobile larvae or larval tracks were observed in four (13.3%) animals. Histological examination confirmed the ophthalmoscopic observations, showing that the lesions were focal and sparse. In one animal, there was a larva in the retina, without inflammatory reaction around it. The results demonstrated that gerbils presented frequent ocular lesions after infection with Toxocara canis, even when infected with a small number of embryonated eggs. The lesions observed were focal, consisting mainly of hemorrhages with signs of reabsorption or inflammation in different segments of eye, and differing from the granulomatous lesions described in ocular larva migrans in humans.

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.

Frequency of toxocara infection in children attended by the health public service of Maringá, south Brazil

The lack of specific laboratorial diagnosis methods and precise symptoms makes the toxocariasis a neglected disease in Public Health Services. This study aims to determine the frequency of Toxocara spp. infection in children attended by the Health Public Service of Hospital Municipal de Maringá, South Brazil. To evaluate the association of epidemiological and clinical data, an observational and cross-section study was carried out. From 14,690 attended children/year aged from seven month to 12 years old, 450 serum samples were randomly collected from September/2004 to September/2005. A questionnaire was used to evaluate epidemiological, clinical and hematological data. An ELISA using Toxocara canis larval excretory-secretory products as antigen detected 130 (28.8%) positive sera, mainly between children from seven month to five years old (p = 0.0016). Significant correlation was observed between positive serology for Toxocara, and frequent playing in sandbox at school or daycare center (p = 0.011) and the presence of a cat at home (p = 0.056). From the families, 50% were dog owners which exposed soil backyards. Eosinophilia (p = 0.776), and signs and symptoms analyzed (fever p = 0.992, pneumonia p = 0.289, cold-like symptoms p = 0.277, cough p = 0.783, gastrointestinal problems p = 0.877, migraine p = 0.979, abdominal pain p = 0.965, joint pain p = 0.686 and skin rash p = 0.105) could not be related to the presence of anti-Toxocara antibodies. Therefore, two asthmatics children showed titles of 1:10,240 and accentuated eosinophilia (p = 0.0001). The authors emphasize the needs of prevention activities.

A simple and inexpensive in vitro method for retrieving fertilized Toxocara canis eggs

The erratic migration of nematode larvae is potentially deleterious for humans, especially those produced by Toxocara roundworms. Diagnosis of human toxocariosis: visceral larva migrans depends on antibody detection against excretions-secretions (E/S) from Toxocara larvae by enzyme-linked immunosorbent assay. In the present work, we wish to propose a simple and cheap culture procedure for keeping T. canis female worms alive. We removed living worms from the small intestine of euthanized puppies at the Canine Control Centre "Culhuacan" in the Southern part of Mexico City. To ascertain the utility of the method, we compared the population size of fertilized eggs from both female worms kept in culture (FCM) and those obtained using uterus excision method (UEM). Operationally, a fertilized egg develops a larva after 1 month. Our results show that the culture method was superior at a ratio of 3:1 over UEM. FCM had advantages over UEM, such as (1) low probability of contamination with foreign antigens, (2) greater safety for infective egg manipulation, and (3) gave rise to a higher percentage of fertile eggs.

[Toxocariasis: clinical and laboratory features in 54 patients]

OBJECTIVE

To describe the clinical and laboratory findings in children with toxocariasis.

METHODS

Fifty-four children with reactive serology to Toxocara determined by ELISA were prospectively identified between January 1998 and September 2000. The patients were divided into three groups: asymptomatic children (n 24), those with visceral larva migrans (n 16) and those with ocular larva migrans (n 14). Age, serology titers, and eosinophil count at diagnosis were compared among the groups. The patients received treatment with albendazole 10-15 mg/kg/day for 15 days or thiabendazole 25 mg/kg/day in two series of 7 days.

RESULTS

The clinical features were as follows: 24 children (44.4 %) were asymptomatic, pneumonitis was found in 9 (16.7 %), hepatomegaly in 6 (11.1 %), acute posterior uveitis in 5 (9.3 %), strabismus in 5 (9.3 %), leukocoria in 4 (7.4 %), fever in 3 (5.6 %). There was 1 case of keratitis, 1 of cataracts, 1 of myocarditis and 1 case of pneumonia with pleural effusion. Some patients showed more than one clinical feature. Four children experienced loss of vision in the affected eye. No differences in age or serology titers were found among the groups. Eosinophil count was lower in the group with ocular larva migrans than in the other groups (p < 0.001). Children with active disease showed clinical improvement and a 70.4 % decrease in eosinophilic count one year after treatment. Serological titers showed an unpredictable pattern during the follow-up.

CONCLUSIONS

Most of the infected children were asymptomatic. In the post-treatment follow-up, clinical improvement and a decrease in eosinophilic count were observed. Further studies are needed to evaluate the efficacy of treatment, especially in asymptomatic children.

Toxocariasis in humans: clinical expression and treatment dilemma

A new scheme of clarifying clinical forms of toxocariasis is proposed to include: (i) systemic forms: classical VLM and incomplete VLM; (ii) compartmentalized forms: ocular and neurological toxocariasis; (iii) covert toxocariasis; and (iv) asymptomatic toxocariasis. The following markers are helpful in defining clinical forms namely, patient characteristics and history, clinical symptoms and signs, positive serology, eosinophilia and increased levels of IgE. Amongst the available drugs albendazole is the most commonly used, although other benzimidazole compounds have a similar efficacy. The recommended dose of albendazole is 15 mg kg(-1) body weight daily for 5 days and in some cases with VLM syndrome the treatment needs to be repeated. An evaluation of treatment efficacy can be made by observing a rise in eosinophilia within a week followed by any improvement in clinical symptoms and signs, lower eosinophilia and serological tests taken over a period of at least 4 weeks. In addition to clinical rationales for the specific treatment of VLM and OLM, preventive treatment needs to be considered bearing in mind the increasing risk of larvae localizing in the brain during the course of an infection. To reduce migration of Toxocara larvae a single course of albendazole is suggested in cases where eosinophilia and serology are at least moderately positive.

Environmental and serological evidence for the presence of toxocariasis in the urban area of Ancona, Italy

To evaluate the Toxocara spp. eggs environmental contamination of the soil of the urban or suburban area Ancona (Italy), 22 public playgrounds were selected and several cores of soil were taken from any selected areas. To study the Toxocara seroprevalence in the inhabitants of Ancona, blood samples were collected from selected groups of individuals. One hundred and sixty-three blood samples were tested using an enzyme linked immunosorbent assay (ELISA) technique (Lofarma Lab, Milan, Italy) for the detection of IgG-specific antibodies to T. canis excretory-secretory antigens. Toxocara spp. eggs were found in the soil samples from 14 (63.6%) playgrounds. Toxocara seroprevalence was detected in blood specimens from six (8.1%) out of 74 symptomatic individuals and from one (1.1%) out of 89 asymptomatic controls. Among symptomatic individuals, the association between Toxocara seroprevalence and eosinophilia resulted statistically significant (p = 0.029). The high environmental contamination frequency found make necessary to prompt preventive public health measures, such as control of stray animals, treatment of infected pets and hygiene education of the population.

Serological evidence of toxocariasis in patients from Spain with a clinical suspicion of visceral larva migrans

Sera from patients with clinical characteristics of toxocariasis were assayed using the ELISA method and larval excretory-secretory antigen. Four hundred and seven samples of Toxocara serology were received at the laboratory of Ciudad Sanitaria Juan Canalejo Hospital of Corunna, Spain, from 1984 to 1989. Of these, 30 were from adults, 332 from children and 45 from patients of unknown age, resulting in Toxocara seroprevalences of 23.3%, 32.8% and 17.7% respectively. The reasons for these serological differences in the rural and urban areas of Galicia, Spain are discussed.

Clinical and laboratorial features of visceral toxocariasis in infancy

Forty children with a diagnosis of Visceral Toxocariasis were evaluated prospectively from February 1982 to June 1989. Diagnosis was established by clinical, laboratory and serological (ELISA - ES Toxocara canis antigen) evaluations. A great clinical polymorphism was found in our patients, ranging from unspecific or absent manifestations to an exuberant symptomatology. The laboratory findings were: leukocytosis, eosinophilia and elevation of serum gammaglobulin and isohemagglutinin levels. No significant relationship between clinical findings and laboratory parameters was found. Serology (ELISA) was a method of great diagnostic support but did not show a correlation with clinical and laboratory findings in this study. There was a significant relationship between pulmonary manifestations and the presence of signs and/or symptoms, when the patients were sent to us. Our findings, especially the high incidence of pulmonary manifestations, suggest that Visceral Toxocariasis has to be included in the differential diagnostic of children with pulmonary manifestations, characteristic epidemiological data and associated eosinophilia.

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.

Toxocara antibodies in patients with visceral or ocular disorder in Slovenia

The incidence of Toxocara antibodies was determined in 319 sera from patients suspected of having Toxocara infection. Serological responses were compared with clinical manifestations and age of the patients. A seropositive reaction was found in 24% of the patients. Highly positive results (OD 0.510-1.000 and OD > 1.000) by ELISA were obtained significantly more frequently in younger patients than in older ones (p < 0.005). The percentage of seropositive patients with visceral disorder was found to decrease with age, whereas the proportion of seropositive patients with ocular disorder increased with age. Serologically confirmed Toxocara infection in Slovenia alerted us to the fact that this health issue should be given due attention in the future.

Asymptomatic toxocariasis in children. A prospective study and treatment trial

Screening of 153 Hispanic children attending a Hospital-based primary care clinic revealed a 16 percent prevalence of Toxocara canis infection. Infections were found in other household occupants for half of these children. Follow-up of 20 children (for periods of up to 7 years) with asymptomatic T. canis infection failed to demonstrate any clinical sequelae. However, longer periods would be necessary to entirely discount the possibility of latent ocular disease. Treatment with thiabendazole did not appear to alter the course of the infection in a controlled 1-year evaluation as measured by eosinophil counts and specific T. canis antibody titers.

Improvements in the serodiagnosis of helminthic zoonoses

Remarkable progress has been achieved in developing improved serodiagnostic assays for a group of diseases for which other diagnostic methods are often lacking. Toxocariasis, trichinellosis, dirofilariasis, Taenia solium cysticercosis and the cystic and alveolar forms of hydatid disease are occult infections in humans and sometimes in lower animal hosts. Although Strongyloides stercoralis achieves patency in humans, parasitologic diagnosis is often very difficult. Efforts to develop reliable immunodiagnostic methods have spanned several decades but progress had been slow until recently. The complexity and nonspecificity of helminth antigens were major problems which prevented the full realization of the benefits of the highly sensitive assay systems now available. Modern immunologic methods including hybridoma technology, immunoaffinity chromatography and immunoblotting, however, have yielded improved reagents and the means to characterize their nature and function. The outcome of this research has been more sensitive and specific serologic tests based on measurement of both circulating antigens and antibodies as well as improved understanding of the nature of host-parasite interactions. Although much remains to be done, many improved immunodiagnostic procedures are already being applied in clinical diagnosis, epidemiologic studies and control programs directed against the helminthic zoonoses.

Ocular Toxocara canis infections: diagnosis by enzyme immunoassay

An enzyme-linked immunoassay (ELISA) was used to establish the sero-prevalence of Toxocara canis infection in several New Zealand populations including those who, through environment or occupation, had close contact with dogs. The prevalence of positive ELISA values found reflected the degree of dog contact, e.g. positive ELISA's occurred in 2.8% of urban adults, 13.9% of dog breeders and 28.4% of hydatid control officers emphasizing that a history of dog contact needs to be considered when ELISA results are interpreted in a clinical context. Ophthalmoscopy of 102 hydatid officers, 28.4% of whom were seropositive, disclosed no evidence of ocular toxocariasis and suggested that the officers might be immunoprotected. Preliminary immunoblot analysis of the range of toxocara excretory/secretory antigens bound to serum immunoglobulin from patients with presumed visceral larva migrans and ocular toxocariasis, showed the same reactivity profile as a positive reference serum and serum from a seroresponsive hydatid control officer.

Zoonotic visceral and ocular larva migrans

Infection of children with the larval stage of the dog roundworm Toxocara canis usually produces few, if any, clinical signs. In some children, however, the disease may be severe, with permanent ocular or neurologic sequelae. Because the prevalence of infection may exceed 10 per cent in some population subgroups, it is important to understand the modes of transmission and risk factors for infection. The clinical presentations of toxocariasis as well as recommendations for their prevention are described.

Immune responses of CBA/J mice to graded infections with Toxocara canis

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.

Evaluation of the common conditions associated with eosinophilia

In an eosinophilic population of 47 boys of the same age, a large proportion (92%) were helminth infested or atopic, or both, compared with 36% of 36 controls. The methods used to detect these conditions were not costly or elaborate, except for the radioallergosorbent test, which was used to measure concentrations of circulating IgE antibodies to atopic allergens. It is suggested that an economical approach to detect helminthiasis and atopy in cases of eosinophilia is adopted using the methods employed here, with skin prick tests replacing the radioallergosorbent test.