Results
A total of 408 participants, including 200 patients with asthma as a case group with a mean ± SD age of 8.19 ± 3.2 years and 208 individuals without asthma as a control group with a mean ± SD age of 7.79 ± 3.4 years, were included in the study. According to the statistical test, both patient and control groups did not differ significantly in age, location, and sex distribution. (P ≥ 0.05) (Table 1) .
The prevalence of Toxocara infection in the study population (patients and control individuals) was 6.9% (95% CI, 3–5.62%; 28/408). Sixteen out of the 200 children with asthma (8%; 95%CI, 2.11–6.49%) and 12 out of the 208 children without asthma (5.8%; 95%CI 2.71–5.9%) were seropositive for anti-Toxocara IgG antibodies. There were no statistically significant differences in the prevalence of toxocariasis between children with asthma and children without asthma (OR, 1.420; 95% CI, 0.654-3.083; P value = 0. 373) (Table 2).
In subgroup analyses based on sociodemographics, Toxocara infection seropositivity was significantly associated with asthma in children whose parents were farmers (OR, 5.647; 95%CI, 1.168-27.299; P-value = 0.017), and those with frequent contact with soil (OR, 3.225; 95%CI, 1.044-9.961; P-value = 0.033). More details and significance for other variables are shown in Table 3.
The multivariate analysis showed that a history of atopic asthma in the family (OR, 3.463; 95% CI, 2.005- 5.982; P-value < 0.001), soil contact (OR, 2.658; 95% CI, 1.675- 4.218; P-value < 0.001), and eating unwashed (raw) vegetables (OR, 2.575; 95% CI, 1.454- 4.558; P-value < 0.001) were independent factors associated with asthma (Table 3). Additionally, no significant association was found between seropositivity to Toxocara spp. and asthma.

Discussion

The prevalence of asthma in children has been reported from 2% to 37% in different parts of the world (10). The prevalence rate of childhood asthma has been reported to be 10.9% in Iran (11). Identifying the risk factors that can affect allergy and asthma is crucial. Some previous experimental and epidemiological studies have suggested that geo-helminth infection, such as toxocariasis, might play an etiological role in developing asthma and other allergic disorders(4, 12) However, according to the hygiene hypothesis, this relationship is still controversial and awaits to be explored (13). This investigation discovered that children with asthma had a greater seroprevalence ofToxocara infection than age- and gender-matched controls, showing that Toxocara seropositivity was not an independent risk factor for developing asthma in this pediatric population in Boyer-Ahmad Province.
Regarding the seroprevalence of toxocariasis in asthmatic and healthy children, the present study was in agreement with some previous epidemiologic studies where no significant difference in Toxocara seropositivity was observed between the two groups (14, 15). In contrast to our study, several studies have reported a statistically significant difference between the seroprevalence of Toxocara infection among asthmatic and healthy children(16-19). In a study by Cobzaru et al., the seroprevalence of toxocariasis in asthmatic children (68.42%) was significantly higher than in the control subjects (13.63%) (16). Moreover, two published meta-analysis studies in 2014 and 2018 indicated that Toxocara infection could be a potential risk factor for developing asthma (20, 21). An explanation for these different results could be attributed to the age of the study population, geographic and environmental conditions in each region, the rate of soil contamination with Toxocara spp. eggs in the studied areas, parasite load, personal hygiene, study design, and different sensitivity and specificity methods used to diagnose toxocariasis (commercial ELISA or Western blot). Although there was no significant difference in the prevalence of toxocariasis between children with and without asthma in this study, asthmatic children who had frequent contact with soil (one of the most important known risk factors for toxocariasis) and those whose fathers were farmers had significantly higher Toxocara seropositivity than healthy children. These findings indicate that this region of Iran is contaminated with Toxocara eggs, and the risk of acquiring infection is high, particularly for children who frequently play in similar conditions in the southwest of Iran. Our study also found that children with a history of atopic asthma in the family, soil contact, and eating unwashed raw vegetables were more susceptible to having asthma. Some studies confirm a positive association between these underlying factors with asthma (22-24). In the present study, the prevalence of toxocariasis in the total study population (asthmatic and non-asthmatic children) was 6.9%. Several case-control studies had a higher overall prevalence than our results (12, 16, 25). For example, in two studies by Momen et al. (in Iran) and Cobzaru et al. (in Romania), the seroprevalence of toxocariasis in the study population was reported to be 33.35.% and 41%, respectively (12, 16). The fact that most of the children in our study lived in the city and their lifestyle was such that the majority had no history of exposure to dogs and cats may explain the lower overall prevalence of toxocariasis in our study compared to most other studies.
On the contrary, some studies report a lower prevalence of toxocariasis than the current study. In this regard, Darvish et al. and Sadri et al. reported the prevalence of toxocariasis at 2.48% and 1.09%, respectively, which may be due to the use of different serological diagnosis methods and antigenic sources(17, 26). A relatively high prevalence of HT is seen in children (6.9%) in current study. Therefore, control and preventive measures against toxocariasis must be considered part of the study region’s healthcare system policies. Some suggested preventive strategies are public education of parents about ways of transmitting the infection, proper fencing around farms and children’s playgrounds, and deworming of dogs and cats. The most critical limitations were the small sample size and the absence of confirming methods for definitive toxocariasis diagnosis (such as Western blotting). Despite the mentioned limitations, using native secretory-excretory antigen (ES) with acceptable sensitivity and specificity significantly reduces cross-reactions (Barr et al. 2014). In a study done by Zibaei et al. to diagnose toxocariasis, the sensitivity and specificity of ELISA using T. cati ES antigens were 97.0% and 96.7% respectively (27). Accurate diagnosis of asthmatic children by an experienced pediatrician in allergy and immunology based on the ISAAC questionnaire and good matching of groups in terms of age, gender, socioeconomic status, and place of residence were among the strengths of our study.