The relationship between Toxocara species seropositivity and allergic skin disorders: a systematic review and meta-analysis
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Ali Rostami,1,* Mehran Amrovani,2
1. Infectious Diseases and Tropical Medicine Research Center, Health Research Institute, Babol University of Medical Sciences, Babol, Iran
2. High Institute for Education and Research in Transfusion Medicine, Tehran, Iran
- Introduction: Allergic skin diseases (ASDs) are a group of itchy, inflammatory skin conditions with substantial morbidity worldwide and negative impact on the quality of life of patients and their families. Atopic dermatitis, prurigo, pruritus, eczema and urticaria are among the most common ASDs. These disorders affect up to 20% of children and up to 5% of adults globally, and their prevalence is increasing worldwide, especially in low-income countries. In routine clinical practice, in the majority of cases the causes of these disorders are not easily identifiable. It has been demonstrated that both genetic and environmental factors play important roles in the development of ASDs. Moreover, it is assumed that infections, including internal parasitic infections, could be an underlying cause of some ASDs .
Toxocara infection is a globally distributed zoonotic disease with an estimated of 2 billion at-risk people worldwide. Human toxocariasis is caused by the larval stage of Toxocara canis and Toxocara cati and rarely by other Toxocara species, which are intestinal nematodes founded in canids and felids as definitive hosts. Human infection occurs by the ingestion of infective eggs of Toxocara through contaminated vegetables, water, soil and hands or by direct contact with puppies and kittens, and children are more at risk for infection. Humans are accidental hosts for Toxocara, and after hatching in the intestine, larvae migrate to other organs or tissues, including the lungs, liver, muscles and central nervous system, without developing into the adult form. Migrating larvae are associated with peripheral blood hypereosinophilia and several clinical manifestations, mostly categorized as ocular larva migrans (OLM), visceral larva migrans (VLM) and neurologic or covert toxocariasis.
Epidemiological evidence suggests that helminth parasites, especially those known as nematodes, have protective effects against atopy and allergic diseases, as allergic diseases are rare in regions with high helminth parasite exposure and common in areas with low or reduced helminth exposure. In contrast to other helminthic infections, it is assumed that Toxocara infection (which has an incomplete life cycle in humans) could trigger the inception of allergic diseases, including asthma, wheezing and atopy. In past years a growing number of studies investigated the possible association between Toxocara infection and the risk of ASDs, however, the results are conflicting. Here, for the first time, we performed a systematic review and metaanalysis on all studies published to date to gain a better understanding regarding the association between Toxocara infection and the development of ASDs. The results of this study may be helpful for clinicians, who should consider toxocariasis as a potential cause of ASDs, allowing for early diagnosis and treatment of ASDs.
- Methods: We searched the MEDLINE, ScienceDirect, Scopus, Web of Science and Google Scholar databases to 15 May 2021 to identify the relevant studies. We used a random effects meta-analysis model to generate the pooled odds ratio (OR) and 95% confidence intervals (CIs).
- Results: Fifteen studies, including eight studies with a case–control design (735 patients and 1342 controls) and seven studies with a cross-sectional design (a total of 4804 participants, 1302 individuals with ASDs and 3502 without ASDs), were included in the meta-analysis. We found an increased risk for ASDs in individuals with Toxocara seropositivity (OR 1.75 [95% CI 1.16 to 2.64]). Subanalysis showed that Toxocara seropositivity was significantly associated with urticaria (OR 2.97 [95% CI 1.53 to 5.76]), however, it was not significantly associated with atopy (OR 1.08 [95% CI 0.55 to 2.15]) and eczema (OR 1.62 [95% CI 0.95 to 2.78]). Moreover, the pooled ORs were 2.34 (95% CI 1.32 to 4.15) and 1.27 (95% CI 0.69 to 2.35) for case-control and cross-sectional studies, respectively.
- Conclusion: The results of our study support hypotheses regarding the existence of a positive relationship between Toxocara infection and allergic disorders, although this association should be further investigated by longitudinal and mechanism studies.
- Keywords: allergy, meta-analysis, skin disorders, Toxocara infection, urticaria
