1. Background
Toxocariasis is a zoonotic helminthic infection caused by the larval stages of Toxocara canis and Toxocara cati, which are common roundworms found in dogs and cats (1). The disease mainly affects children under five years-of-age. Human infection occurs through ingestion of embryonated eggs from the soil, dirty hands, uncooked vegetables, and paratenic hosts (2). The most widely recognized source of human infection is ingestion of contaminated soil followed by paratenic hosts (2-7). The released larvae from the eggs or paratenic hosts enter the circulation which then invade and form granulomas in different tissues, including; liver, lungs, eyes, brain and other tissues (8, 9). The prevalence of toxocariasis due to soil contamination with Toxocara spp. eggs is from 6.6% to 87.1% (10-14).
Inflammatory responses and eosinophilia are the most common signs of a Toxocara infection (4, 8). In helminthic diseases, moderate to severe eosinophilia occurs as a pathophysiologic response to the parasitic infection and toxocariasis is one of the main causes of eosinophilia, regardless of the presence of signs and symptoms or organ injury, in infected individuals (15). However, in many cases a peripheral eosinophilia is not connected to toxocariasis (16). High seroprevalence rates of toxocariasis have been reported in hypereosinophilic patients. Seo and Yoon in a seroepidemiological study in Korea, reported that out of a total of 101 eosinophilic patients, 50.5% were found to be positive by a Toxocara ELISA (17). In another study in Korea, the seroprevalence of toxocariasis among healthy people with eosinophilia was reported to be 67.0% (18). In a relatively similar study, the seroprevalence of toxocariasis among asymptomatic children with eosinophilia in Croatia was found to be 31% (19). Maraghi et al. in a study conducted in Khuzestan, southern Iran, found that 19% of eosinophilic individuals were seropositive for toxocariasis (20).
2. Objectives
The aim of the present study was to determinate and compare the rate of toxocariasis in normal and hypereosinophilic individuals in Shiraz, southern Iran.
3. Patients and Methods
In this cross-sectional study which was carried out during February 2010 to April 2012, serum samples were collected from 100 patients with hypereosinophilia and 100 subjects with a normal eosinophil count (1-6%), who were referred to the three main university affiliated hospitals in Shiraz, Fars Province, southern Iran. The control group was composed of outpatients who attended the outpatient clinics or hospitals for a routine checkup, or those who had no obvious infectious diseases.
Sample size was calculated based on the prevalence rate of a previously published study on the seroprevalence of toxocariasis in the region, and the sample size of similar studies. There were 21 patients with a peripheral blood eosinophilia of 10% or higher which were considered as hypereosinophilia (15). Demographic features of the participants were recorded in a predesigned questionnaire during sample collecting. Written informed consent was obtained from the participants, or their parent or guardian, where the participants were children. All sera were tested for IgG antibodies to Toxocara spp. by an enzyme-linked immunosorbent assay (ELISA, IBL/Germany) according to the manufacturer’s instructions. The test utilized an immunoassay to detect anti-Toxocara canis excretory-secretory antigens (TES). Cut-off value was 10 U, while 9-11 U was considered as a gray zone, < 9 U was negative, and > 11 was positive. Based on the data sheet of the ELISA kit, the sensitivity and specificity of the kit are reported to be > 95%. Collected data were analyzed by SPSS (Version 16.0. Chicago, SPSS Inc). Chi-square was used to compare the seroprevalence rate in the two groups.
4. Results
In the hypereosinophilic patients, 54 (54%) were male, and 46 (46%) were female, while in the normal individuals, 58 cases (58%) were male, and 42 (42%) were female. The differences in gender and age of the participants were insignificant (P = 0.46 and 0.59 respectively). The range of eosinophilia found in the patients was between 10-77%. Anti-Toxocara antibodies were detected in the serum of 2 (2%) of the hypereosinophilic patients and 3 (3%) of the normal individuals. No significant correlation was found between hypereosinophilia and the presence of anti-Toxocara antibodies in this study (P = 0.65). Moreover, no association was found between seropositivity to Toxocara and the age or sex of the participants (P = 0.53 and 0.49, respectively). Table 1 shows the age distribution of the participants and seropositivity to toxocariasis.
Table 1. Age Distribution of the Study’s Participants and Seropositivity to Toxocariasis
| Age Group, y | Frequency | Positive Toxocara IgG | ||
|---|---|---|---|---|
| With Eosinophilia | Without Eosinophilia | With Eosinophilia | Without Eosinophilia | |
| 1-10 | 18 | 7 | 0 | 0 |
| 11-20 | 9 | 9 | 0 | 0 |
| 21-30 | 14 | 14 | 1 | 1 |
| 31-40 | 12 | 11 | 0 | 0 |
| 41-50 | 8 | 15 | 0 | 1 |
| 51-60 | 16 | 15 | 1 | 0 |
| > 60 | 23 | 29 | 0 | 1 |
| Total | 100 | 100 | 2 | 3 |
5. Discussion
Human toxocariasis is a helminthic zoonotic disease with a worldwide distribution. Seroprevalence studies in different areas of the world have documented the rate of infection to be as high as 80% in some areas (1). In Iran, the seroprevalence of toxocariasis varies between 2.7% and 29.3% in different areas of the country (21-24). Manifestations of toxocariasis are diverse and non-characteristic, and in many cases they are also asymptomatic. Like other tissue dwelling parasites, Toxocara induces moderate to severe eosinophilia in infected individuals (1, 8). Therefore, hypereosinophilia is a key finding for the diagnosis of toxocariasis when the other reasons for this symptom have been ruled out. Peripheral blood eosinophilia is one of the most important features of human toxocariasis. This phenomenon can be seen in visceral larva migrants (VLM). However, due to the low larval burden, eosinophilia is not present in ocular larva migrants (OLM) patients. Moreover, some toxocariasis patients may have toxocariasis without eosinophilia.
Hypergammaglobulinemia and elevated concentrations of total serum IgE are the other laboratory findings of toxocariasis. Patients with an increase in the concentration of serum total IgE > 500 IU/mL, along with one or more clinical signs, might be considered as toxocariasis (25). In many studies conducted on the seroprevalence of toxocariasis, a higher rate of infection has been reported in eosinophilic patients in comparison with non-eosinophilic subjects. However, such correlation has not been seen in several other studies (17). In a study conducted by Maraghi et al. in the south of Iran, serum samples from 100 individuals with peripheral blood eosinophilia, and from another 100 individuals without eosinophilia, were evaluated for anti-Toxocara antibodies. Antibodies were found in 19 (19%) of the eosinophilic individuals and only 1% of the control group (20). In another study, in Turkey, IgG antibodies specific to Toxocara were detected in 114 (32.6%) of the eosinophilic patients in comparison with 71 (20.3%) of the non-eosinophilic individuals (26). In our study no difference was found between the seropositivity rates of toxocariasis between the two groups.
Detection of anti-Toxocara antibodies in a non-eosinophilic subject might be due to a past infection. Such findings have been reported in different studies where healthy subjects are seropositive for toxocariasis (27, 28). On the other hand, the low prevalence rate of toxocariasis in both eosinophilic and normal individuals in our study might be due to the age of the subjects, who were mainly over 50 years-of-age. In a previous study which was conducted in the region about 12 years ago, the prevalence of toxocariasis in children was 25.6% (24).
Our findings are consistent with a study by Kim et al. in South Korea, where they did not find a significant correlation between the IgG ELISA titer for Toxocara and the level of eosinophilia (17). In our study, no association was found between the sex or age of participants and seropositivity to toxocariasis. A comparable finding was reported by Dogan et al. in Turkey, where they reported a similar seropositivity rate of Toxocara antibodies between age groups and genders (29).
Further studies with a relatively large sample of patients, with and without eosinophilia, and composed of different age groups, are needed to clarify any association between hypereosinophilia and toxocariasis in the region. Hypereosinophilia might be due to increased infections with Toxocara larva and a low rate of infection might result in lower eosinophilia (30). Hypereosinophilia can occur for a variety of reasons and toxocariasis is only one of these, but testing should be carried out for patients with suspected toxocariasis to rule out a Toxocara infection in hypereosinophilic individuals.
