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

Who Let the Dogs Out? Unmasking the Neglected: A Semi-Systematic Review on the Enduring Impact of Toxocariasis, a Prevalent Zoonotic Infection

Toxocariasis remains an important neglected parasitic infection representing one of the most common zoonotic infections caused by the parasite Toxocara canis or, less frequently, by Toxocara cati. The epidemiology of the disease is complex due to its transmission route by accidental ingestion of embryonated Toxocara eggs or larvae from tissues from domestic or wild paratenic hosts. Even though the World Health Organization and Centers for Disease Control classified toxocariasis amongst the top six parasitic infections of priority to public health, global epidemiological data regarding the relationship between seropositivity and toxocariasis is limited. Although the vast majority of the infected individuals remain asymptomatic or experience a mild disease, the infection is associated with important health and socioeconomic consequences, particularly in underprivileged, tropical, and subtropical areas. Toxocariasis is a disease with multiple clinical presentations, which are classified into five distinct forms: the classical visceral larva migrans, ocular toxocariasis, common toxocariasis, covert toxocariasis, and cerebral toxocariasis or neurotoxocariasis. Anthelmintic agents, for example, albendazole or mebendazole, are the recommended treatment, whereas a combination with topical or systemic corticosteroids for specific forms is suggested. Prevention strategies include educational programs, behavioral and hygienic changes, enhancement of the role of veterinarians, and anthelmintic regimens to control active infections.

Review of Toxocariasis at a Children's Hospital Prompting Need for Public Health Interventions

BACKGROUND

Toxocariasis, caused the by dog and cat roundworm, is one of the most common zoonotic helminth infections in the United States and can lead to severe lifelong morbidity in children. Although historical seroprevalence studies have identified a high frequency of toxocariasis regionally in the United States, there are few studies linking epidemiology and clinical disease in children. The study objective was to examine the contemporary epidemiology of pediatric toxocariasis within an endemic US region.

METHODS

We conducted an epidemiologic study analyzing children diagnosed with toxocariasis presenting to a tertiary pediatric hospital in Texas from 2010 to 2021. We examined risk factors and performed a geospatial analysis, including a comparative analysis of human cases and locations of surrendered infected stray animals in the same region.

RESULTS

Children diagnosed with toxocariasis were most commonly of Hispanic/Latino ethnicity (30/46; 65%), white race (41/45; 91%) and receiving Medicaid (34/44, 77%). Many infected children had contact with dogs or cats. Ocular toxocariasis was associated with a lack of peripheral eosinophilia ( P < 0.001). No other Toxocara syndromes were associated with defined absolute eosinophil count levels. Post-treatment resolution of eosinophilia was variable, ranging from 1 to 172 weeks. A Toxocara hotspot was identified in northeast Houston, comprising one of the lowest median household incomes in the region.

CONCLUSIONS

Toxocariasis is a devastating zoonotic infection in children living in the US. As it is not a reportable disease, the true burden remains unknown. It is critical to increase awareness of toxocariasis to direct public health interventions and ultimately reduce Toxocara -induced morbidity in US children.

Allergic asthma manifestations in human and seropositivity to Toxocara, a soil-transmitted helminth of carnivores: A case-control study and scoping review of the literature

Asthma is a common respiratory disease affecting humans. Helminth parasites, including Toxocara species, have been implicated as predisposing factors of asthma. However, various studies present different findings on asthma-Toxocara association. Herein, we investigated the association of asthma manifestations with Toxocara seropositivity in a case-control setting on 248 participants (147 women and 101 men), with 124 healthy individuals as the control group and 124 patients known to have asthma based on the medical records of asthma clinics of Kerman University of Medical Sciences. Consequently, we presented a scoping review of all previous studies carried out on this topic, summarizing current findings and existing knowledge on this issue. Of 248 participants, 31 (12.5%) were Toxocara-seropositive, of which 19 (15.3%) were in the patient group and 12 (9.7%) in the control group. A significant relationship was found between asthma severity and age in Toxocara-seropositive individuals (P < 0.04). We found no significant relationship between asthma and Toxocara seropositivity. We identified 7,724 related records in three major scientific databases, NCBI PubMed, Scopus, and Google Scholar. The review of the literature showed that there are 80 published articles on asthma-Toxocara relationship with contradictory findings. More than half of the studies were performed in only four countries, namely, Brazil, the Netherlands, the United States, and Iran. The study population in 70% of the studies were children, and few studies investigated asthma-Toxocara association in adults. The most common study designs for investigating the association of asthma and Toxocara seropositivity were cross-sectional (35.0%), case-control (27.5%), and animal experimental (12.5%) studies. This study found no significant relationship between asthma manifestations and toxocariasis in a case-control setting. However, a scoping review of the current literature suggests that further experimental and field longitudinal cohort studies are required to elucidate the nature of asthma-Toxocara interaction in humans.

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

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

The global prevalence of Toxocara spp. in pediatrics: a systematic review and meta-analysis

BACKGROUND

Toxocariasis is a zoonotic parasitic disease caused by Toxocara canis and Toxocara cati in humans. Various types of T. canis are important.

PURPOSE

The current study aimed to investigate the prevalence of Toxocara spp. in pediatrics in the context of a systematic review and meta-analysis.

METHODS

The MEDLINE (PubMed), Web of Sciences, Embase, Google Scholar, Scopus, and Cumulative Index of Nursing and Allied Health databases were searched to identify peer-reviewed studies published between January 2000 and December 2019 that report the prevalence of Toxocara spp. in pediatrics. The evaluation of articles based on the inclusion and exclusion criteria was performed by 2 researchers individually.

RESULTS

The results of 31 relevant studies indicated that the prevalence of Toxocara spp. was 3%-79% in 10,676 cases. The pooled estimate of global prevalence of Toxocara spp. in pediatrics was 30 (95% confidence interval, 22%-37%; I2=99.11%; P=0.00). The prevalence was higher in Asian populations than in European, American, and African populations.

CONCLUSION

Health policymakers should be more attentive to future research and approaches to Toxocara spp. and other zoonotic diseases to improve culture and identify socioeconomically important factors.

Prevalence and Molecular Characterization of Toxocara cati Infection in Feral Cats in Alexandria City, Northern Egypt

Background

This study was performed to determine the prevalence and to identify precisely Toxocara spp., which infects feral cats in Alexandria, Egypt based on morphological and molecular approaches.

Methods

This cross-sectional study was carried out on 100 feral cats trapped from different areas of Alexandria during 2018. Adult male and female worms were recovered from small intestinal contents after euthanasia and dissection of cats. Distinct morphological features were initially determined using available keys, and then after amplification and sequencing of the mitochondrial NADH dehydrogenase subunit 1 (nad1) gene was carried out and phylogenetic trees were constructed.

Results

Forty out of 100 cats were infected with Toxocara spp. Intensity of infection ranged from 1 to 9 worms/cat, with a mean of 2.27±1.6. All isolates were confirmed as T. cati based on morphological features and the sequence of nad1 gene. Results of the current study clearly show that Egyptian T. cati isolate examined herein is genetically similar to those recorded in other countries.

Conclusion

The current work revealed high prevalence of T. cati in feral cats in the study area. This is the first genetic study that confirms T. cati from feral cats in Egypt. In addition, it demonstrated the suitability and need of genetic markers such as nad1 for identification of Toxocara spp. Furthermore highlights the public health importance of T. cati in Egypt.

Evidence for Asthma in the Lungs of Mice Inoculated with Different Doses of Toxocara canis

Toxocara canis, a common roundworm that mainly causes toxocariasis, is a zoonotic parasite found worldwide. Humans, an accidental host, can acquire T. canis infection through accidental ingestion of T. canis-embryonated egg-contaminated food, water, and soil, and by encapsulated larvae in a paratenic host's viscera or meat. Long-term residence of T. canis larvae in a paratenic host's lungs may induce pulmonary inflammation that contributes to lung injury, airway inflammatory hyperresponsiveness, and collagen deposition in mice and clinical patients. This study intended to investigate the relationship between T. canis infection and allergic asthma in BALB/c mice inoculated with high, moderate, and low doses of T. canis eggs for a 13-week investigation. The airway hyperresponsiveness (AHR) to methacholine, collagen deposition, cytokine levels, and pathological changes in lung tissues was assessed in infected mice at weeks 1, 5, and 13 postinfection. The cell composition in bronchoalveolar lavage fluid of infected mice was assessed at weeks 5 and 13 postinfection. Compared with uninfected control mice, all groups of T. canis-infected mice exhibited significant AHR, a dose-dependent increase in eosinophilic infiltration leading to multifocal interstitial and alveolar inflammation with abundant mucus secretion, and collagen deposition in which the lesion size increased with the infective dose. Infected mice groups also showed significant expressions of eotaxin and type 2 T-helper-dominant cytokines such as interleukin (IL)-4, IL-5, and IL-13. Overall, these results suggest that T. canis larval invasion of the lungs may potentially cause pulmonary inflammatory injury and could subsequently contribute to the development of allergic manifestations such as asthma.

Toxocara species environmental contamination of public spaces in New York City

Human toxocariasis has been identified as an under-diagnosed parasitic zoonosis and health disparity of significant public health importance in the United States due to its high seropositivity among socioeconomically disadvantaged groups, and possible links to cognitive and developmental delays. Through microscopy and quantitative PCR, we detected that Toxocara eggs are widespread in New York City public spaces, with evidence of significant levels of contamination in all five boroughs. The Bronx had the highest contamination rate (66.7%), while Manhattan had the lowest contamination rate (29.6%). Moreover, infective eggs were only found in the Bronx playgrounds, with over 70% of eggs recovered in embryonic form and the highest egg burden (p = 0.0365). All other boroughs had eggs in the pre-infectious, unembronyated form. Toxocara cati, the cat roundworm, was the predominant species. These results suggest that feral or untreated cats in New York City represent a significant source of environmental contamination. These findings indicate that human toxocariasis has emerged as an important health disparity in New York City, with ongoing risk of acquiring Toxocara infection in public spaces, especially in poorer neighborhoods. There is a need for reducing environmental Toxocara contamination. Additional rigorous public health interventions should explore further approaches to interrupt transmission to humans.

Toxocara canis and Toxocara cati are helminth worms that infect dogs and cats, respectively. Infected dogs and cats will defecate thousands of Toxocara eggs into the environment. Humans are incidental hosts and are exposed when consuming contaminated soils via the fecal-oral route. After leaving the gastrointestinal tract, the Toxocara larvae will enter the vasculature and can migrate to any major organ system, including lungs, ocular, and central nervous system. Symptoms can range from mild muscle aches to severe asthma, blindness, and encephalitis. Humans are not definitive hosts of the parasite and cannot transmit Toxocara eggs to the environment or other humans. There is a need for research on the sanitary impact of Toxocara for both humans and animals, especially in large urban cities such as New York City. Poverty is also associated with higher rates of toxocariasis, with more contamination in poorer neighborhoods where animal control, deworming of pets, and less sanitary conditions exist. This study aims to understand further the disparity of lower socioeconomic areas having higher rates of contaminated parks and playgrounds, comparing the five boroughs of New York City.

Evaluation of the effect of Toxocara cati infection in the mouse model of allergic asthma: Exacerbation of allergic asthma symptoms and Th2 types of response

Toxocariasis is considered a neglected disease despite the importance of Toxocara spp. infections for human health and is little recognized as a significant problem by public health institutions in developing countries. Epidemiological studies suggest that infection with Toxocara cati contributes to the development of allergic asthma.In the present study, we investigated the effect of T. cati infection on experimental allergic airway inflammation using murine model. BALB/c mice were infected by oral administration with 500 embryonated T. cati eggs followed by ovalbumin (OVA) sensitization and challenge to induce allergic airway inflammation. Infection with T. cati in combination with OVA treatment leads to exacerbation of pulmonary inflammation, eosinophilia, airway hyperresponsiveness, OVA specific IgE. Cytokines measurement in bronchoalveolar lavage indicated that the levels of IL-4 and IL-5 in BAL fluid significantly increased after T. cati infected, OVA treated or a combination of both. Increased level of IL-5 was measured in the lungs of T. cati-infected or OVA-treated mice compared with controls. Moreover, combining infection and OVA treatment significantly increase the level of these cytokines. A direct association between T. cati infection and asthma was found in murine model. Although a wide range of helminth species have been demonstrated to modulate allergic responses, most notably the intestinal nematode T. cati, increases airway hyperresponsiveness, lung histopathology, eosinophil recruitment, and Th2 cytokines in alum-sensitized models of airway allergy.

Toxocariasis: A neglected infection for the Anthropocene epoch

While ascariasis, trichuriasis, and hookworm infection dominate global efforts to control human soil-transmitted helminth infections, a picture is unfolding to suggest that toxocariasis is now a fourth and perhaps equally important parasitic disease. Toxocara eggs are widespread in the environment and practically ubiquitous in the soils of many subtropical and tropical regions of Asia, Africa, and the Americas. Human zoonotic infection is also highly prevalent in these areas, based on serologic studies to detect anti-Toxocara antibodies. The relevance of these findings to human and animal disease burden estimates is still largely unknown, but some studies implicate exposure to Toxocara eggs and larvae to both pulmonary disease leading to asthma, and neurologic disease resulting in epilepsy and cognitive delays. On that basis, human toxocariasis may emerge as one of the most important neglected parasitic infections of humans. With anticipated global warming and urbanization associated with our modern human-transformed geological epoch, known as the Anthropocene, it is likely that toxocariasis will become a dominant infection and one widely prevalent in our future and projected mega-cities.

Toxocara seroprevalence in the USA and its impact for individuals and society

Toxocara species are intestinal helminths of dogs and cats, the larval stages of which may infect humans and cause severe neural, ocular and visceral larva migrans disease. Such cases of severe overt disease represent only a small fraction of the of the US population who have been exposed and infected with Toxocara, subsequently developing IgG antibodies to the larvae. The true impact of exposure to Toxocara in this large group of Americans remains uncertain. Toxocara antibody positivity is associated with poverty, but other specific risk factors have been identified, including sex, age, rural residence, region of residence, race and exposure to pets. This seropositive status has also been associated with several childhood diseases, including asthma and epilepsy, increased serum lead levels, and poor neurocognitive function. Three large-scale NHANES studies have provided comprehensive datasets, while several smaller studies have explored specific disease associations. Each seroprevalence study must be interpreted in consideration of the sensitivity and specificity of the individual serological methods employed. This chapter summarizes all historical Toxocara prevalence data from dogs, cats and soil in the United States. It then carefully examines all previous human Toxocara seroprevalence surveys performed in the United States. Data from these surveys is assimilated, compared and discussed to determine the validity of findings and to accurately identify risk factors for Toxocara seropositivity. The validity of associations of exposure to Toxocara larvae and childhood diseases such as asthma and epilepsy and effects neurocognitive function within the American context are also explored.

Toxocara: Protecting pets and improving the lives of people

Toxocara sp. are zoonotic parasitic roundworms that cause infection and morbidity in both developed and developing countries. In humans, infection is thought to be most common in children, particularly those living in poverty, and usually results from consumption of soil contaminated with parasite eggs deposited by dog or cat faeces. Infection in humans results in different clinical manifestations, some more overt like visceral or ocular larva migrans and others more cryptic like neurocognitive delay. Despite its pervasiveness, toxocariasis has become a neglected infection. We review the dynamics of the human-animal interface in the context of this parasite, discuss the challenges in controlling transmission to humans, and cite key areas of research that could enable improved interventions. With political will and proper resource allocation, we propose that effective interventions are possible in the near term.

Toxocariasis and the clinical spectrum

Toxocara canis and T. cati are among the most widely distributed helminthic species in the world with a high zoonotic impact. Millions of people are infected^a and hundreds of thousands are suffering from toxocarosis, a disease encompassing four different entities: larva migrans visceralis (VLM) syndrome, ocular larva migrans (OLM) syndrome, covert toxocarosis (covT), common toxocarosis (comT) and neurotoxocarosis (NT). Toxocara infections in humans may remain clinically inapparent but may also induce severe diseases. This contribution gives a synoptic overview of the most important historical, clinical, diagnostic and therapeutical aspects of toxocarosis in humans.

Parasites and allergy: Observations from Brazil

Brazil is a middle-income country undergoing the epidemiological transition. Effects of changes in daily life habits and access to clean water, sanitation and urban services on a growing urban population have contributed to a double burden of both infectious and noncommunicable chronic diseases. Studies have indicated that parasite infections may modulate the human immune system and influence the development of allergic conditions such as asthma. However, there is no consensus in the published literature on the effects of parasitic infections on allergy, perhaps as a consequence of factors determining the epidemiology of these infections that vary between populations such as age of first infection, duration and chronicity of infections, parasite burden and species, and host genetic susceptibility. In this review, we discuss the observations from Brazil concerning the relationship between parasite infections and allergy.

Toxocara sero-prevalence and its relationship with allergic asthma in asthmatic patients in north-eastern Iran

Toxocariasis is an important neglected tropical disease that has been suggested as a possible etiologic agent of asthma. The objective of the present study was to investigate possible significant association between Toxocara seroprevalence and asthma in a clinic-based case-control study. Blood samples were collected from human subjects aged 5-70 years, 50 of whom had signs of asthma and 50 of whom had no signs of asthma. Risk factors for asthma and Toxocara spp. infection were assessed by a questionnaire given to each patient. Blood samples were analysed to measure levels of anti-Toxocara spp. immunoglobulin G (IgG). Patients with bronchial asthma were observed to have higher Toxocara spp. seropositivity than that of the non-asthmatic controls (6 vs 2%, P = 0.47). The mean anti-Toxocara spp. antibody titre was not significantly higher in patients with bronchial asthma than in individuals without asthma (P = 0.395, 95% CI = 0.579-1.45). There was no significant difference in the mean age, sex, social class, exposure to smoking and presence of domestic dog or cat at home between the two groups (P ≥ 0.05). The presence of anti-Toxocara spp. IgG was statistically associated with higher blood eosinophils, but it was not associated with asthma (P ≥ 0.05). The observed relationship between exposure to Toxocara spp. infection and bronchial asthma in Iranian patients warrants further evaluation. An understanding of any potential influence on the pathogenesis of human asthma provides a potential avenue for prevention.

Seroprevalence of ToxocaraCanis in Asthmatic Children and its Relation to the Severity of Diseases - a Case-Control Study

Background

Toxocariasis is a common parasitic infectionworldwide even in developed countries. Through this health problem, the immune system is triggered and the antibody is produced, leading to some hypersensitive situations like asthma. In the present study, we tried to show a correlation between Toxocara Canis (T. canis) seropositivityand asthma in Isfahan city.

Methods

This research is a cross-sectional study involving 40 asthmatics and 46 non-asthmatic cases aged 2-18 years. In all cases, T. canis IgG level was measured using enzyme-linked immunosorbent assay (ELISA) and compared between two groups.

Results

The seroprevalence of IgG anti-T. canis antibodies were 45%in the asthmatic patients and 21.7% in thecontrols (P= 0.022). The more severe asthmatic patients had significantly more risk for T. canis seropositivity (P= 0.019). In the asthmatic patients, there was a significant correlation between Toxocara seropositivity and goingto park or playground (P= 0.001).

Conclusion

In this study, we found a significantly positive serology of T. canis in asthmatic children especially in more severe disease. To verify the etiologic role of Toxocara in asthma, more advanced studies are needed.

Toxocara spp. infection and risk of childhood asthma: A systematic review and meta-analysis

Asthma is one of the most common chronic respiratory disease worldwide, with a negative impact on quality of life and socio-economic status of patients. There are some evidences to suggest that Toxocara infection is a neglected risk factor for childhood asthma. We performed a systematic review and meta-analysis to further understanding of this relationship. Five databases include PubMed, Science Direct, Scopus, Web of Science (ISI), and Google scholar were searched (up to October 2017) to identify the relevant studies. We used random-effects meta-analysis model to estimate the pooled odds ratio (OR) and 95% confidence intervals (CI). Heterogeneity was assessed with the Q-test and I² statistic. A total of 17 studies including 11 studies with case-control design (1139 patients and 1023 controls) and six studies with cross-sectional design (a total of 5469 participants, 872 asthmatics, and 4597 non-asthmatics children) met the eligibility criteria. An increased risk for asthma was observed in children with Toxocara infection seropositivity (OR, 1.91; 95% CI, 1.47-2.47). In sub-group analysis, the pooled ORs were (OR, 2.13; 95% CI, 1.43-3.15) and (OR, 1.73; 95% CI, 1.23-2.44) for case-control and cross-sectional studies, respectively. Moreover, considering to specific IgE seropositivity, a pooled OR of 2.36 (95% CI, 0.93-5.98) was observed. In conclusion, this meta-analysis revealed that children infected with Toxocara spp. are more likely to have asthma compared to non-infected children. More studies (especially longitudinal studies) are needed to further investigate the impact of Toxocara spp. infection on the onset or development of asthma.

Zoonotic helminth exposure and risk of allergic diseases: A study of two generations in Norway

BACKGROUND

Animal and human studies indicate that definitive host helminth infections may confer protection from allergies. However, zoonotic helminths, such as Toxocara species (spp.), have been associated with increased allergies.

OBJECTIVE

We describe the prevalence of Toxocara spp. and Ascaris spp. seropositivity and associations with allergic diseases and sensitization, in 2 generations in Bergen, Norway.

METHODS

Serum levels of total IgG4, anti-Toxocara spp. IgG4 and Ascaris spp. IgG4 were established by ELISA in 2 cohorts: parents born 1945-1972 (n = 171) and their offspring born 1969-2003 (n = 264). Allergic outcomes and covariates were recorded through interviews and clinical examinations including serum IgEs and skin prick tests.

RESULTS

Anti-Ascaris spp. IgG4 was detected in 29.2% of parents and 10.3% of offspring, and anti-Toxocara spp. IgG4 in 17.5% and 8.0% of parents and offspring, respectively. Among offspring, anti-Toxocara spp. IgG4 was associated with pet keeping before age 15 (OR = 6.15; 95% CI = 1.37-27.5) and increasing BMI (1.16[1.06-1.25] per kg/m² ). Toxocara spp. seropositivity was associated with wheeze (2.97[1.45- 7.76]), hayfever (4.03[1.63-9.95]), eczema (2.89[1.08-7.76]) and cat sensitization (5.65[1.92-16.6]) among offspring, but was not associated with allergic outcomes among parents. Adjustment for childhood or current pet keeping did not alter associations with allergies. Parental Toxocara spp. seropositivity was associated with increased offspring allergies following a sex-specific pattern.

CONCLUSIONS & CLINICAL RELEVANCE

Zoonotic helminth exposure in Norway was less frequent in offspring than parents; however, Toxocara spp. seropositivity was associated with increased risk of allergic manifestations in the offspring generation, but not among parents. Changes in response to helminth exposure may provide insights into the increase in allergy incidence in affluent countries.

Seroprevalence of Toxocariasis in Children with Urticaria: A Population-based Study

OBJECTIVE

This study described the prevalence of IgG class antibodies against Toxocara spp. and their association with urticaria in 2- to 12-year-old children.

METHODS

This population-based cross-sectional study was conducted between May 2012 and September 2014. The study sample comprised 168 children. Blood samples were collected to verify the presence of toxocariasis by using ELISA to detect IgG antibodies. The guardians of the children were interviewed to characterize the presence or absence of other diseases, such as urticaria.

RESULTS

The presence of urticaria was observed in 38% of participants. The seroprevalence of toxocariasis in this population was 16%. This study confirmed a positive association between urticaria and positive serology for Toxocara and a negative independent association with canine contact and the number of household residents.

CONCLUSIONS

There are no previous reports in the literature of a population-based study that correlates the presence of urticaria with serology for toxocariasis.

Risk factors for Toxocara spp. seroprevalence and its association with atopy and asthma phenotypes in school-age children in a small town and semi-rural areas of Northeast Brazil

Toxocara canis, Toxocara cati, are roundworms that live in the intestines of dogs and cats, respectively, and are predominantly agents of human toxocariasis. Studies have suggested that Toxocara spp. seroprevalence increases levels of total and aeroallergen-specific IgE (sIgE), asthma prevalence and asthma morbidity. Nevertheless, other work reported a negative association between Toxocara spp. seropositivity with skin hypersensititity and a positive association with sIgE. The objective of the present study was to evaluate risk factors for acquiring Toxocara spp. infection and to investigate possible significant association between its seroprevalence with atopy and asthma. Students from elementary schools, residents in a small town and its surroundings of Northeast Brazil, underwent blood sampling to measure levels of anti-Toxocara spp. IgG, peripheral blood eosinophils, and specific IgE to aeroallergens. We used univariable and multivariable logistic regression analyses to assess possible risk factors for Toxocara spp. seropositivity and its association with atopy, wheeze/asthma with asthma phenotypes, in a sample of 791 elementary school children aged 6-13 years. Toxocara spp. seroprevalence reached 63.6%; 49.9% had sIgE; 7.2% and 3.3% had atopic wheeze/asthma and non-atopic wheeze/asthma respectively. Risk factors associated with Toxocara spp. seropositivity were: contact with dogs (adj. OR 2.33; 95% CI=1.70-3.19) and cats (adj. OR 3.09; 95% CI=2.10-4.55), and male sex (adj. OR 2.21; 95% CI=1.62-3.02). The presence of anti-Toxocara IgG was statistically associated with blood eosinophils >4% and >10% (adj. OR 1.84; 95% CI=1.33-2.55 and adj. OR 2.07; 95% CI=1.45-2.97, respectively), and atopy (adj. OR 2.00; 95% CI=1.49-2.68), but it was not associated with wheeze/asthma. Concluding, the results obtained in this study showing the association of Toxocara spp. seroprevalence with sIgE may suggest a possible immunological cross-reactivity between IgE epitopes from Toxocara spp. and aeroallergens.

The Hygiene Hypothesis and Its Inconvenient Truths about Helminth Infections

Current iterations of the hygiene hypothesis suggest an adaptive role for helminth parasites in shaping the proper maturation of the immune system. However, aspects of this hypothesis are based on assumptions that may not fully account for realities about human helminth infections. Such realities include evidence of causal associations between helminth infections and asthma or inflammatory bowel disease as well as the fact that helminth infections remain widespread in the United States, especially among populations at greatest risk for inflammatory and autoimmune diseases.

Seroepidemiology of human Toxocara and Ascaris infections in the Netherlands

Toxocara canis, Toxocara cati and Ascaris suum are worldwide-distributed zoonotic roundworms of dogs, cats and pigs, respectively. The epidemiology of these parasites in developed countries is largely unclear. Two countrywide cross-sectional serosurveys were therefore conducted in the Netherlands in 1995/1996 and 2006/2007 to investigate the prevalence, trends and risk factors for human Toxocara and Ascaris infections in the general population. The Netherlands is characterized by high pig production, freedom from stray dogs and virtual absence of autochthonous infections with the human-adapted roundworm Ascaris lumbricoides. Over the 10 years between the two serosurveys, Toxocara seroprevalence decreased significantly from 10.7 % (n = 1159) to 8.0 % (n = 3683), whereas Ascaris seroprevalence increased significantly from 30.4 % (n = 1159) to 41.6 % (n = 3675), possibly reflecting concomitant improvements in pet hygiene management and increased exposure to pig manure-contaminated soil. Increased anti-Toxocara IgGs were associated with increasing age, male gender, contact with soil, ownership of cats, cattle or pigs, hay fever, low education, high income and non-Western ethnic origin. Increased anti-Ascaris IgGs were associated with increasing age, owning pigs, low education, childhood geophagia and non-Dutch ethnic origin. Besides identifying specific groups at highest risk of Toxocara and Ascaris infections, our results suggest that these infections mainly occur through environmental, rather than foodborne, routes, with direct contact with soil or cat and pig ownership being potentially modifiable exposures.

Toxocariasis and childhood asthma: A case-control study

OBJECTIVE

The objective of this study is to investigate the association between anti-Toxocara IgG seropositivity and asthma in children.

METHODS

This was a case-control study conducted in a university hospital in south Brazil between May 2012 and June 2013. Were recruited 208 children up to 12 years old of whom 156 had asthma (cases) and 52 did not have asthma (controls), with a case-control ratio of 3:1 matched by age. Children's parents or guardians were interviewed using a structured questionnaire with closed questions. Serology was performed using enzyme-linked immunosorbent assay (ELISA) with excretory-secretory antigen of Toxocara canis (TES).

RESULTS

The seroprevalence of IgG anti-T. canis antibodies was 12.8% in the cases and 7.7% in the controls. There was no significant association between seropositivity to T. canis and risk of asthma (adjusted odds ratio [OR]: 1.89, 95% CI: 0.52 to 6.89, p = 0.33). Household income < 2 minimum salaries, paternal school years < 9, allergic rhinitis in children, a positive family history of asthma and rhinitis and contact with cats were significantly associated with asthma, with adjusted ORs (95% CIs) of 3.05 (1.21 to 7.73), 2.83 (1.11 to 7.18), 10.5 (4.32 to 25.6), 2.65 (1.14 to 6.17), 2.49 (1.07 to 5.78) and 2.73 (1.03 to 7.27), respectively.

CONCLUSIONS

This study did not find a statistically significant association between seropositivity to Toxocara sp. and risk of asthma in children. Low family income, low paternal education level, concomitant allergic rhinitis, family history of asthma and allergic rhinitis and contact with cats were independent factors associated with childhood asthma.

Knowledge gaps in the epidemiology of Toxocara: the enigma remains

Toxocara species infect a wide range of companion, domestic and wild animals as definitive and paratenic hosts, via multiple routes of transmission, producing long-lived tissue-inhabiting larvae and resistant eggs that can survive in the external environment. Therefore Toxocara and the disease it causes in humans, toxocariasis, represents an ideal aetiological agent for the development of the one health approach. However, despite increasing awareness of the public health significance of toxocariasis, gaps in our understanding of certain key aspects of the parasite's biology and epidemiology remain. These gaps hinder our ability to integrate research effort within the veterinary, medical and environmental disciplines. This review will highlight key deficits in our understanding of nine dimensions of Toxocara epidemiology and discuss a potential scenario to develop a more integrated, one health approach to improve our understanding of the prevention and control of this complex and cryptic zoonosis.

Study of Toxocara seroprevalence among patients with allergy and healthy individuals in Bulgaria

Data in the literature addressing the ability of Toxocara infection in humans to induce development of atopic disease are controversial. The aim of our study was to determine the seroprevalence of anti-Toxocara antibodies in three groups of people: subjects with allergic symptoms and presence of allergen-specific IgE, subjects with allergic symptoms and absence of allergen-specific IgE, and clinically healthy blood donors. Serum samples from all subjects were tested by ELISA and Western blot for presence of specific antibodies against Toxocara canis. The results of our study did not support the link between toxocariasis and allergic manifestations in atopic patients. Among subjects with allergic symptoms and absence of atopy was found seroprevalence of 2·2% in Western blot. Same index in patients with atopy was 0·8%, and in clinically healthy blood donors 4·0%. Our study gives us grounds to consider that it is appropriate persons with allergic reactions, without evidence of atopy to be tested for presence of anti-Toxocara antibodies in the course of their diagnostic evaluation. Data from clinically healthy persons suggest that there is a 'hidden' infection among the population, which is not clinically manifested.

[Cardiovascular manifestations of human toxocariasis]

Toxocariasis is a parasitic infection produced by helminths that cannot reach their adult stage in humans. For their etiological species (Toxocara canis and Toxocara cati), man is a paratenic host. Infection by such helminths can produce a variety of clinical manifestations, such as: visceral larvae migrans syndrome, ocular larvae migrans syndrome and covert toxocariasis. In the visceral larvae migrans syndrome, the organs that are mainly involved include liver, lungs, skin, nervous system, muscles, kidneys and the heart. Regarding the latter, the importance of cardiovascular manifestations in toxocariasis, as well as its clinical relevance, has increasingly begun to be recognized. The current article is based on a systematic information search, focused mainly on the clinical and pathological aspects of cardiovascular manifestations in toxocariasis, including its pathophysiology, laboratory findings, diagnosis and therapeutical options, with the objective of highlighting its importance as a zoonosis and its relevance to the fields of cardiovascular medicine in adults and children.

Proteinases in excretory-secretory products of Toxocara canis second-stage larvae: zymography and modeling insights

Components released in excretory-secretory products of Toxocara canis larvae (TES) include phosphatidylethanolamine-binding proteins (TES26), mucins (TES120, MUC2-5), and C-type lectins (TES32, TES70) and their biochemical, immunological, and diagnostic properties have been extensively studied albeit proteinase activities towards physiological substrates are almost unknown. Proteolytic activities in TES samples were first analyzed by gel electrophoresis with gelatin as substrate. Major activities of ~400, 120, and 32 kDa in TES were relatively similar over a broad pH range (5.5–9.0) and all these were of the serine-type as leupeptin abolished gelatinolysis. Further, the ~400 kDa component degraded all physiological substrates tested (laminin, fibronectin, albumin, and goat IgG) and the 120 kDa component degraded albumin and goat IgG while proteinases of lower MW (45, 32, and 26 kDa) only degraded laminin and fibronectin, preferentially at alkaline pH (9.0). By protein modeling approaches using the known sequences of TES components, only TES26 and MUC4 displayed folding patterns significantly related to reference serine proteinases. These data suggest that most of serine proteinase activities secreted in vitro by infective larvae of T. canis have intriguing nature but otherwise help the parasite to affect multiple components of somatic organs and bodily fluids within the infected host.

Asthma and toxocariasis

BACKGROUND

Asthma is the most common chronic disease in children and a major public health problem in adults. A relation between asthma and toxocariasis has been hypothesized.

OBJECTIVE

To evaluate the strength of association between asthma and Toxocara species seropositivity by conducting a systematic review and a meta-analysis of available data.

METHODS

PubMed, EMBASE, Web of Science, and the reference lists of all relevant articles and books were screened until October 2013. Two authors independently assessed eligibility and study quality and extracted data. A common odds ratio was estimated using a random-effects meta-analysis model of aggregated published data.

RESULTS

Ten studies met the inclusion criteria, for a total of 1,530 participants (723 cases and 807 controls). This meta-analysis found a significantly higher prevalence of Toxocara canis infection in patients with asthma than in controls (odds ratio 3.36, 95% confidence interval 1.76-6.42, P < .001). Similar results were found when meta-analysis was restricted to the studies considering only children or adults.

CONCLUSION

The results support the existence of a positive association between asthma and Toxocara species seropositivity.

Neglected parasitic infections in the United States: toxocariasis

Toxocariasis is a preventable parasitic disease that is caused by the dog and cat roundworms Toxocara cani and T. cati, respectively. Humans become infected when they accidently ingest infectious Toxocara eggs commonly found in contaminated soil; children are most often affected. Clinical manifestations of Toxocara infection in humans include ocular toxocariasis and visceral toxocariasis. Although infection with Toxocara can cause devastating disease, the burden of toxocariasis in the United States population remains unknown. In addition, risk factors for acquiring infection need to be better defined, and research needs to be conducted to better understand the pathophysiology and clinical course of toxocariasis. Development of diagnostic tests would enable clinicians to detect active infection, and determination of optimal drug regiments would ensure patients were appropriately treated. Addressing these public health gaps is necessary to understand and address the impact of toxocariasis in the United States.

Ascaris lumbricoids Infection as a Risk Factor for Asthma and Atopy in Rural Bangladeshi Children

Controversy persists as to whether helminth infections cause or protect against asthma and atopy. The aim of this study was to investigate the effects of helminth infection on asthma and atopy among Bangladeshi children. A total of 912 children aged 4.5 years (mean = 54.4, range = 53.5–60.8 months) participated in a cross-sectional study nested into a randomized controlled trial in Bangladesh. Ever-asthma, ever-wheezing and current wheezing were identified using the International Study of Asthma and Allergies in Childhood questionnaire. Current helminth infection was defined by the presence of helminth eggs in stools, measured by routine microscopic examination. Repeated Ascaris infection was defined by the presence of anti-Ascaris IgE ≥ 0.70 UA/ml in serum measured by the CAP-FEIA method. Atopy was defined by specific IgE to house dust mite (anti-DP IgE) ≥ 0.70 UA/ml measured by the CAP-FEIA method and/or positive skin prick test (≥ 5 mm). Anti-Ascaris IgE was significantly associated with ever asthma (odds ratio (OR) = 1.86, 95% CI: 1.14–3.04, highest vs. lowest quartile; P for trend 0.016). Anti-Ascaris IgE was also significantly associated with positive anti-DP IgE (OR = 9.89, 95% CI: 6.52–15.00, highest vs. lowest; P for trend < 0.001) and positive skin prick test (OR = 1.69, 95% CI: 1.01–2.81, highest vs. lowest, P for trend 0.076). These findings suggest that repeated Ascaris infection is a risk factor for asthma and atopy in rural Bangladeshi children. Further analysis is required to examine the mechanism of developing asthma and atopy in relation to helminth infection.

Toxocariasis and lung function: relevance of a neglected infection in an urban landscape

Toxocariasis has been highlighted as a potentially important neglected infection of poverty in developed countries that experience substantive health disparities such as the United States. An association between Toxocara infection and lung function, in concert with a relatively high prevalence of infection, may mark an important mechanism by which this infection could contribute significantly to the differential morbidity across different socioeconomic groups and landscapes. To assess the potential relevance of this infection in a dense urban environment, we measured the association between forced expiratory volume in 1 second (FEV₁) and serology diagnosed Toxocara infection in a sample of US-born New York City residents. We identified a significant independent association between Toxocara infection and lung function, wherein those with previous Toxocara infection had a 236.9 mL reduced FEV₁ compared to those without Toxocara infection even after adjusting for age, sex, ethnicity, level of education, smoking status, body mass index, and pet ownership. These findings from New York City corroborate similar findings in a national sample and, while the cross-sectional data preclude a direct causal relationship, this study identifies a potentially important neglected infection in a dense urban landscape.

Molecular and phylogenetic study on Toxocara vitulorum from cattle in the mid-Delta of Egypt

Toxocara vitulorum is an important intestinal nematode that commonly infects ruminants world-wide, notably in tropical and sub-tropical regions. In Egypt, T. vitulorum has a high prevalence rate in cattle and buffaloes calves. The current work aims to identify and verify T. vitulorum collected from cattle in El-Mahlla El-Kubra city in the mid-Delta of Egypt, using molecular and phylogenetic tools. The first internal transcribed spacer (ITS-1) and 18S genes of ribosomal DNA were amplified, sequenced, and compared with nucleotide sequences deposited in data bases, and also used to construct the phylogenetic trees. Our results confirm that T. vitulorum isolated from cattle in Egypt is genetically identical to those recorded in other countries. Moreover, the phylogenetic trees show a close relationship among different species of Toxocara, including the zoonotic species. Our results show that ITS genes can be targeted as genetic markers to diagnose and discriminate among different Toxocara spp. The data presented here may be helpful in the pursuit of further molecular and genetic studies of Toxocara species.

Ocular toxocariasis

Ocular toxocariasis is an uncommon worldwide parasitic infection that affects mostly children and is found in both rural and metropolitan areas. In many parts of the world, parasitic infections of the eye are a major cause of blindness. The diagnosis of toxocariasis is essentially clinical, based on the lesion morphology and supportive laboratory data such as serum enzyme-linked immunosorbent assay (ELISA) titers and ELISA Toxocara titers on aqueous humor; other diagnostic methods are imaging studies including optical coherence tomography, fluorescein angiography, computed tomography, and ocular ultrasound. Treatment is directed at complications arising from intraocular inflammation and vitreous membrane traction. Early vitrectomy may be of value both diagnostically and therapeutically.

Toxocara seropositivity, atopy and asthma: a study in Cuban schoolchildren

INTRODUCTION

Evidence suggests that human toxocariasis (HT) could stimulate the onset of allergic diseases such as asthma. More specifically, in subjects having a hypothetical 'atopic genotype', HT could boost preexistent allergy symptoms. We tested the latter hypothesis in Cuba, a country where both asthma and HT are prevalent.

MATERIAL AND METHODS

In a group of Cuban school-aged children (n = 958), we investigated the association of Toxocara seropositivity and atopic status with asthma. Toxocara seropositivity was diagnosed with ELISA and atopy by allergen skin prick test. Both physician-diagnosed asthma and current wheeze, as determined by International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire, were considered. Associations were assessed using multivariable logistic regression analyses, with either 'physician-diagnosed asthma' or 'current wheeze' as outcome variable.

RESULTS

40.1% of the children were Toxocara seropositive. Prevalences were 21.7% for current wheeze and 32.7% for physician-diagnosed asthma. The odds of having asthma were almost two times higher in atopic children, but only reached borderline significance (OR=1.90, CI 95%: 0.95-3.80 for physician-diagnosed asthma and OR=1.94, CI 95%: 0.98-3.85 for current wheeze). Toxocara seropositivity and physician-diagnosed asthma were associated (OR=1.51, CI 95%: 1.01-2.26). Moreover, in children without antibodies to Toxocara, being atopic was significantly associated with having physician-diagnosed asthma (OR=2.53, CI 95%: 1.63-3.90), while this association was not present in Toxocara positives (OR=1.38, CI 95%: 0.82-2.37).

CONCLUSION

Our data confirm previous observations of higher Toxocara seropositivity rates in asthmatic children. Toxocara seropositivity appeared to abrogate the apparent association between atopy and asthma in Cuban children. Although this observation was limited to physician-diagnosed asthma, it challenges the hypothesis that HT stimulates the onset of allergic diseases such as asthma in atopic individuals.

Toxocara seropositivity, atopy and wheezing in children living in poor neighbourhoods in urban Latin American

Background

Toxocara canis and T. cati are parasites of dogs and cats, respectively, that infect humans and cause human toxocariasis. Infection may cause asthma-like symptoms but is often asymptomatic and is associated with a marked eosinophilia. Previous epidemiological studies indicate that T. canis infection may be associated with the development of atopy and asthma.

Objectives

To investigate possible associations between Toxocara spp. seropositivity and atopy and childhood wheezing in a population of children living in non-affluent areas of a large Latin American city.

Methods

The study was conducted in the city of Salvador, Brazil. Data on wheezing symptoms were collected by questionnaire, and atopy was measured by the presence of aeroallergen-specific IgE (sIgE). Skin prick test (SPT), total IgE and peripheral eosinophilia were measured. Toxocara seropositivity was determined by the presence of anti-Toxocara IgG antibodies, and intestinal helminth infections were determined by stool microscopy.

Findings

Children aged 4 to 11 years were studied, of whom 47% were seropositive for anti-Toxocara IgG; eosinophilia >4% occurred in 74.2% and >10% in 25.4%; 59.6% had elevated levels of total IgE; 36.8% had sIgE≥0.70 kU/L and 30.4% had SPT for at least one aeroallergen; 22.4% had current wheezing symptoms. Anti-Toxocara IgG was positively associated with elevated eosinophils counts, total IgE and the presence of specific IgE to aeroallergens but was inversely associated with skin prick test reactivity.

Conclusion

The prevalence of Toxocara seropositivity was high in the studied population of children living in conditions of poverty in urban Brazil. Toxocara infection, although associated with total IgE, sIgE and eosinophilia, may prevent the development of skin hypersensitivity to aeroallergens, possibly through increased polyclonal IgE and the induction of a modified Th2 immune reaction.

Toxocara canis and T. cati are roundworms found in dogs and cats, respectively, that can also infect humans and cause several clinical features, including asthma-like symptoms. Human infections with T. canis have been associated with an increased prevalence of atopy and asthma. In the present study, we investigated the associations between Toxocara seropositivity with eosinophilia, total IgE, specific IgE and skin prick test reactivity to aeroallergens, as well as atopic and non-atopic wheezing. Toxocara seropositivity was associated with elevated eosinophil counts and total and aeroallergen-specific IgE but was also associated with a decreased prevalence of skin prick test. Toxocara seropositivity was not associated with atopic wheezing. In conclusion, our data show that human toxocariasis, although associated with eosinophilia and raised levels of total and allergen-specific IgE, may play a role in the modulation of allergic effector responses in the skin.

Pet roundworms and hookworms: a continuing need for global worming

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

Association between contamination of public squares and seropositivity for Toxocara spp. in children

A concomitant study was carried out, of the association of positive serology for Toxocara spp. in 90 children who played in public squares used for leisure, with the frequency with which each child used these areas, and the presence of eggs of Toxocara spp. in the sand or grass in these locations. The sand and grass of their peridomiciles and school playgrounds, as well as the feces of their dogs were also analyzed for Toxocara. Serum samples were tested for IgG antibodies to Toxocara canis excreted-secreted larval antigens by ELISA, and blood samples for eosinophilia. The water-sedimentation technique was used to evaluate the presence of parasite eggs in the sand and grass turfs, and in feces of the dogs that also frequented these locations. 16/90 (17.8%) of the children were seropositive for Toxocara spp. There was a positive association between seropositivity in children who played in the public squares six or seven times a week, with a parasite load above 1.1 eggs/g of sand, as well as with contamination of the peridomicile, even at less than 1.0 egg/g of sand. Eosinophilia, the habit of geophagy, age from one to four years, and the presence of parasitized pet dogs were also positively correlated with seropositivity in the children. Eggs were found in 15/15 (100%) of the public squares, 17/90 (18.9%) of the peridomiciles, 3/13 (23.1%) of the schools, and 12/41 (29.3%) of the dogs living in the peridomiciles investigated.

Visceral larva migrans in immigrants from latin america

To determine whether increased migration is associated with an increase in incidence of toxocariasis (visceral larva migrans), we analyzed clinical data obtained from immigrants from Latin America. Although infection with Toxocara sp. roundworm larvae is distributed worldwide, seroprevalence is highest in tropical and subtropical areas.