Toxocara seroprevalence in adults with bronchial asthma

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.

Dirofilaria immitis Could Be a Risk Factor for the Development of Allergic Diseases in Humans

Simple Summary

Heartworm is a parasitic infection transmitted by mosquitoes to animals and humans. The risk of human infections is high in those areas with high canine prevalence, such as the Canary Islands. In these islands, there is also a high number of allergic inhabitants. Since some studies have shown a relationship between parasite infections and development of allergies, the aim of this study was to evaluate whether exposure to heartworm may contribute to the development of allergies. A survey carried out on dog owners in the Canary Islands showed that 51.3% of allergic owners had a heartworm-positive dog, and significant differences were found between allergic or not-allergic owners, according to whether the dog was negative or positive to heartworm. Furthermore, 66 serum samples from inhabitants of the Canary Islands were analyzed for the presence of unspecific allergy markers (Immunoglobulin E or IgE) and specific for heartworm (IgE against Dirofilaria immitis and Wolbachia) and the results show that people who were in contact with heartworm showed total IgE and specific IgE against heartworm more frequently. Contact with heartworm may be a risk factor for the development of allergic diseases, although further studies to elucidate the relationship between heartworm and allergies should be carried out.

Abstract

The Canary Islands are hyperendemic for canine heartworm and the risk of zoonotic infection is high. Additionally, there is evidence of development of allergies due to nematode infections in animals and humans. Since the population of the Canary Islands presents high prevalence of allergic comorbidities, and previous studies have shown a possible relationship between allergies and seropositivity to heartworm, the aim was to evaluate whether exposure to heartworm may contribute to the development of allergies in the human population. First, an epidemiological study was conducted on 248 owners of dogs with/without heartworm infection in the Canary Islands. Secondly, a serological analysis of the presence of total IgE and specific IgE against heartworm was conducted in 66 samples of inhabitants of the Canary Islands. The survey showed that allergic owners had heartworm-positive dogs more frequently (p < 0.01). Of the analyzed human samples, 43.9% were seropositive to heartworm and Wolbachia. Total IgE concentrations were increased in 34.5% seropositive samples and 8.1% seronegative samples. Specific IgE against heartworm was only found in human seropositive samples (17.2%). Contact with heartworm may be a risk factor for the development of allergic diseases, although further studies to elucidate the relationship between heartworm and allergies should be carried out.

Sources and seroprevalence of toxocariasis in Turkey

Toxocariasis in humans is considered a rare disease in Turkey, and the absence of specific symptoms of this disease is probably the main reason for clinicians to underestimate and underdiagnose the disease. Although there are several seroepidemiological studies on visceral larva migrans in the country, a comparison between them is difficult as the serological tests are not standardised. After the introduction of the easily accessible ELISA kit in the market, the number of seroepidemiological studies has increased in which the reported rates ranged between 1% and 56%. Similar to other countries, Toxocara seropositivity in Turkey is more common in men, childhood, in those living in rural area, having a low income level, owning dogs, and biting their nails or practicing geophagia. In addition, toxocariasis is a risk factor for veterinarians, farmers, and pet-shop workers. Toxocara seroprevalence is significantly higher in respiratory, neuropsychiatric, musculoskeletal, skin and abdominal disorders. There are also many studies showing the importance of eosinophilia in toxocariasis. In conclusion, although there are many studies on toxocariasis in Turkey, it is still not well understood to what extent the infection is responsible for a plethora ascribed symptoms. Standardisation of the diagnostic methods and the use of molecular techniques could further throw light in the real epidemiology and the role played by the infection to induce signs and symptoms.

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.

Visceral larva migrans detection using PCR-RFLP in BALB/c mice infected with Toxocara canis

Toxocara canis is an important zoonotic roundworm distributed worldwide. The infective larvae of T. canis are one of the causes of visceral larva migrans (VLM), a clinical syndrome in humans. Diagnosing VLM is difficult, and the differential diagnosis of the larval development stage is limited. Therefore, this experimental research aimed to diagnose T. canis larvae using a molecular method, not only in liver tissue, which is the most commonly affected tissue, but also in the limb muscles, lungs and brain tissues. For this purpose, 24 BALB/c mice were infected with 1000 embryonated T. canis eggs. Necropsies were performed on the second, fourth, seventh and 14th days post-infection. While a part of the samples were digested with pepsin-HCl, the molecular method was used for the remainder of the samples to replicate the mitochondrial DNA adenosine triphosphate (ATP) synthase subunit-6 gene region of T. canis. BbsI, a restriction endonuclease, was used to determine the specificity of the amplicons obtained from Polymerase chain reaction (PCR). The detection limit for embryonated eggs was recorded. The PCR results showed that the sensitivity of the PCR analysis was 83.3% in the liver (with 88.8% accuracy), 87.5% in the lungs (with 91.6% accuracy) and 75.0% in the brain, forelimb and hindlimb muscles (with 83.3% accuracy). In all tissues, the test specificity was determined to be 100%. In this study, the molecular method was applied to only experimentally infected BALB/c mice tissues; thus, it is suggested that it can be also employed in different paratenic hosts and materials possibly infected with T. canis.

Detection and Identification of Toxocara Canis in Infected Dogs Using PCR

Faecal samples were collected from 224 dogs (47 villages) in Ankara. Toxocara spp. eggs were diagnosed in faeces using centrifugal flotation and sedimentation methods. A total of 21 dogs (9.38 %) were positive for Toxocara spp. eggs. In this study, we used the PCR technique that, in combination with DNA sequencing, allows the detection and identification of T.canis eggs in faeces of infected dogs. For this purpose, the ATPase subunit-6 gene (mtDNA) was selected as a target for the amplification T. canis. The primers were used to amplify 217 bp region. Amongst 21 coproscopically detected Toxocara isolates from dogs, 5 (23.8 %) samples were PCR-positive for T. canis, and the remaining 16 samples were PCR-negative. Results indicate that PCR can detect Toxocara canis DNA in faeces of infected dogs, but efficacy was low when compare to sedimentation/flotation. PCR is additional test for diagnosing of this infection. But, the difficulties of identification based on PCR in faecal examinations need to be investigated further.

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.

Detection of Specific Antibody Reactivity to Toxocara Larval Excretory-secretory Antigens in Asthmatic Patients (5-15 Years)

BACKGROUND & PURPOSE

Humans act as an intermediate host for Toxocara canis and Toxocara cati. Toxocara may be an important risk factor for asthma in humans. The aim of the present study was to evaluate immunoglobulin G (IgG) anti-Toxocara canis antibody, using enzyme-linked immunosorbent assay (ELISA) in asthmatic patients (aged 5-15 years), referring to a clinic of pulmonary diseases in Arak, Iran.

MATERIALS & METHODS

In this bi-group cross sectional study, serum samples were collected from 110 children with confirmed asthma and 70 children without asthma within one year. IgG anti-Toxocara antibody was detected viaELISA method. The collected data were analyzed, using SPSS.

RESULTS

The seroprevalence of antibodies against Toxocara species was estimated at 1.8% (two males) in asmathic children viaELISA method; however, no antibodies against Toxocara canis were detected in the control group. There was no significant correlation between the frequency of antibodies against Toxocara and variables such as age, gender, or place of residence (P>0.05). Moreover, the frequency of antibodies against Toxocara was not significantly correlated with contact with dogs, consumption of unwashed fruits and vegetables, or use of raw/undercooked sheep liver (P>0.05).

CONCLUSION

The present study showed anti-Toxocara antibody in 1.8% of asthmatic children and determined the seroprevalence of toxocariasis in asthmatic children and adolescents in Arak, Iran. Based on the findings, the low rate of infection with Toxocara among asthmatic children may be attributed to acceptable personal hygiene and religious considerations.

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.

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.

Toxocara canis: larval migration dynamics, detection of antibody reactivity to larval excretory-secretory antigens and clinical findings during experimental infection of gerbils (Meriones unguiculatus)

In this study, Mongolian gerbils were used to analyse features of Toxocara infection that included larval migration, humoral immune responses to Toxocara canis excretory-secretory antigens (TES) and aspects of host physiology. At day 10 post-infection (p.i.) most larvae were in the intestine and the lungs while later the total number of larvae was higher in the carcass tissue; the number of larvae per gram of tissue was lower elsewhere other than in the brain. Infected animals showed several neurological abnormalities, an early increase in leukocyte and neutrophil levels, two peaks of peripheral eosinophilia (5 and 40 d.p.i.) and high antibody levels against TES in the circulation and in the vitreous humor. A sequential recognition of eight T.canis larval antigens with MW from 24 to 200 kDa was detected by Western blot. The results obtained in this study further support the use of gerbils as an experimental model for systemic, ocular and cerebral toxocariasis.